Find Usages Diff Raw Download HTML Widget
Start line:  
End line:  

Snippet Preview

Snippet HTML Code

Stack Overflow Questions 
1
   /*
2
    * Copyright (c) 1997, 2011, Oracle and/or its affiliates. All rights reserved.
3
    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4
    *
5
    * This code is free software; you can redistribute it and/or modify it
6
    * under the terms of the GNU General Public License version 2 only, as
7
    * published by the Free Software Foundation.  Oracle designates this
8
    * particular file as subject to the "Classpath" exception as provided
9
    * by Oracle in the LICENSE file that accompanied this code.
10
   *
11
   * This code is distributed in the hope that it will be useful, but WITHOUT
12
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14
   * version 2 for more details (a copy is included in the LICENSE file that
15
   * accompanied this code).
16
   *
17
   * You should have received a copy of the GNU General Public License version
18
   * 2 along with this work; if not, write to the Free Software Foundation,
19
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20
   *
21
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22
   * or visit www.oracle.com if you need additional information or have any
23
   * questions.
24
   */
25
  
26
  package java.util;
This class consists exclusively of static methods that operate on or return collections. It contains polymorphic algorithms that operate on collections, "wrappers", which return a new collection backed by a specified collection, and a few other odds and ends.

The methods of this class all throw a NullPointerException if the collections or class objects provided to them are null.

The documentation for the polymorphic algorithms contained in this class generally includes a brief description of the implementation. Such descriptions should be regarded as implementation notes, rather than parts of the specification. Implementors should feel free to substitute other algorithms, so long as the specification itself is adhered to. (For example, the algorithm used by sort does not have to be a mergesort, but it does have to be stable.)

The "destructive" algorithms contained in this class, that is, the algorithms that modify the collection on which they operate, are specified to throw UnsupportedOperationException if the collection does not support the appropriate mutation primitive(s), such as the set method. These algorithms may, but are not required to, throw this exception if an invocation would have no effect on the collection. For example, invoking the sort method on an unmodifiable list that is already sorted may or may not throw UnsupportedOperationException.

This class is a member of the Java Collections Framework.

Author(s):
Josh Bloch
Neal Gafter
Since:
1.2
See also:
Collection
Set
List
Map
69
  
70
  
71
  public class Collections {
72
      // Suppresses default constructor, ensuring non-instantiability.
73
      private Collections() {
74
      }
75
  
76
      // Algorithms
77
  
78
      /*
79
       * Tuning parameters for algorithms - Many of the List algorithms have
80
       * two implementations, one of which is appropriate for RandomAccess
81
       * lists, the other for "sequential."  Often, the random access variant
82
       * yields better performance on small sequential access lists.  The
83
       * tuning parameters below determine the cutoff point for what constitutes
84
       * a "small" sequential access list for each algorithm.  The values below
85
       * were empirically determined to work well for LinkedList. Hopefully
86
       * they should be reasonable for other sequential access List
87
       * implementations.  Those doing performance work on this code would
88
       * do well to validate the values of these parameters from time to time.
89
       * (The first word of each tuning parameter name is the algorithm to which
90
       * it applies.)
91
       */
92
      private static final int BINARYSEARCH_THRESHOLD   = 5000;
93
      private static final int REVERSE_THRESHOLD        =   18;
94
      private static final int SHUFFLE_THRESHOLD        =    5;
95
      private static final int FILL_THRESHOLD           =   25;
96
      private static final int ROTATE_THRESHOLD         =  100;
97
      private static final int COPY_THRESHOLD           =   10;
98
      private static final int REPLACEALL_THRESHOLD     =   11;
99
      private static final int INDEXOFSUBLIST_THRESHOLD =   35;

    
Sorts the specified list into ascending order, according to the natural ordering of its elements. All elements in the list must implement the java.lang.Comparable interface. Furthermore, all elements in the list must be mutually comparable (that is, e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the list).

This sort is guaranteed to be stable: equal elements will not be reordered as a result of the sort.

The specified list must be modifiable, but need not be resizable.

Implementation note: This implementation is a stable, adaptive, iterative mergesort that requires far fewer than n lg(n) comparisons when the input array is partially sorted, while offering the performance of a traditional mergesort when the input array is randomly ordered. If the input array is nearly sorted, the implementation requires approximately n comparisons. Temporary storage requirements vary from a small constant for nearly sorted input arrays to n/2 object references for randomly ordered input arrays.

The implementation takes equal advantage of ascending and descending order in its input array, and can take advantage of ascending and descending order in different parts of the same input array. It is well-suited to merging two or more sorted arrays: simply concatenate the arrays and sort the resulting array.

The implementation was adapted from Tim Peters's list sort for Python ( TimSort). It uses techiques from Peter McIlroy's "Optimistic Sorting and Information Theoretic Complexity", in Proceedings of the Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, January 1993.

This implementation dumps the specified list into an array, sorts the array, and iterates over the list resetting each element from the corresponding position in the array. This avoids the n2 log(n) performance that would result from attempting to sort a linked list in place.

Parameters:
list the list to be sorted.
Throws:
java.lang.ClassCastException if the list contains elements that are not mutually comparable (for example, strings and integers).
java.lang.UnsupportedOperationException if the specified list's list-iterator does not support the set operation.
java.lang.IllegalArgumentException (optional) if the implementation detects that the natural ordering of the list elements is found to violate the java.lang.Comparable contract
152
 
153
     public static <T extends Comparable<? super T>> void sort(List<T> list) {
154
         Object[] a = list.toArray();
155
         Arrays.sort(a);
156
         ListIterator<T> i = list.listIterator();
157
         for (int j=0; j<a.length; j++) {
158
             i.next();
159
             i.set((T)a[j]);
160
         }
161
     }

    
Sorts the specified list according to the order induced by the specified comparator. All elements in the list must be mutually comparable using the specified comparator (that is, c.compare(e1, e2) must not throw a ClassCastException for any elements e1 and e2 in the list).

This sort is guaranteed to be stable: equal elements will not be reordered as a result of the sort.

The specified list must be modifiable, but need not be resizable.

Implementation note: This implementation is a stable, adaptive, iterative mergesort that requires far fewer than n lg(n) comparisons when the input array is partially sorted, while offering the performance of a traditional mergesort when the input array is randomly ordered. If the input array is nearly sorted, the implementation requires approximately n comparisons. Temporary storage requirements vary from a small constant for nearly sorted input arrays to n/2 object references for randomly ordered input arrays.

The implementation takes equal advantage of ascending and descending order in its input array, and can take advantage of ascending and descending order in different parts of the same input array. It is well-suited to merging two or more sorted arrays: simply concatenate the arrays and sort the resulting array.

The implementation was adapted from Tim Peters's list sort for Python ( TimSort). It uses techiques from Peter McIlroy's "Optimistic Sorting and Information Theoretic Complexity", in Proceedings of the Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, January 1993.

This implementation dumps the specified list into an array, sorts the array, and iterates over the list resetting each element from the corresponding position in the array. This avoids the n2 log(n) performance that would result from attempting to sort a linked list in place.

Parameters:
list the list to be sorted.
c the comparator to determine the order of the list. A null value indicates that the elements' natural ordering should be used.
Throws:
java.lang.ClassCastException if the list contains elements that are not mutually comparable using the specified comparator.
java.lang.UnsupportedOperationException if the specified list's list-iterator does not support the set operation.
java.lang.IllegalArgumentException (optional) if the comparator is found to violate the Comparator contract
214
 
215
     public static <T> void sort(List<T> list, Comparator<? super T> c) {
216
         Object[] a = list.toArray();
217
         Arrays.sort(a, (Comparator)c);
218
         ListIterator i = list.listIterator();
219
         for (int j=0; j<a.length; j++) {
220
             i.next();
221
             i.set(a[j]);
222
         }
223
     }


    
Searches the specified list for the specified object using the binary search algorithm. The list must be sorted into ascending order according to the natural ordering of its elements (as by the sort(java.util.List) method) prior to making this call. If it is not sorted, the results are undefined. If the list contains multiple elements equal to the specified object, there is no guarantee which one will be found.

This method runs in log(n) time for a "random access" list (which provides near-constant-time positional access). If the specified list does not implement the RandomAccess interface and is large, this method will do an iterator-based binary search that performs O(n) link traversals and O(log n) element comparisons.

Parameters:
list the list to be searched.
key the key to be searched for.
Returns:
the index of the search key, if it is contained in the list; otherwise, (-(insertion point) - 1). The insertion point is defined as the point at which the key would be inserted into the list: the index of the first element greater than the key, or list.size() if all elements in the list are less than the specified key. Note that this guarantees that the return value will be >= 0 if and only if the key is found.
Throws:
java.lang.ClassCastException if the list contains elements that are not mutually comparable (for example, strings and integers), or the search key is not mutually comparable with the elements of the list.
255
 
256
     public static <T>
257
     int binarySearch(List<? extends Comparable<? super T>> list, T key) {
258
         if (list instanceof RandomAccess || list.size()<)
259
             return Collections.indexedBinarySearch(list, key);
260
         else
261
             return Collections.iteratorBinarySearch(list, key);
262
     }
263
 
264
     private static <T>
265
     int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key)
266
     {
267
         int low = 0;
268
         int high = list.size()-1;
269
 
270
         while (low <= high) {
271
             int mid = (low + high) >>> 1;
272
             Comparable<? super T> midVal = list.get(mid);
273
             int cmp = midVal.compareTo(key);
274
 
275
             if (cmp < 0)
276
                 low = mid + 1;
277
             else if (cmp > 0)
278
                 high = mid - 1;
279
             else
280
                 return mid; // key found
281
         }
282
         return -(low + 1);  // key not found
283
     }
284
 
285
     private static <T>
286
     int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)
287
     {
288
         int low = 0;
289
         int high = list.size()-1;
290
         ListIterator<? extends Comparable<? super T>> i = list.listIterator();
291
 
292
         while (low <= high) {
293
             int mid = (low + high) >>> 1;
294
             Comparable<? super T> midVal = get(i, mid);
295
             int cmp = midVal.compareTo(key);
296
 
297
             if (cmp < 0)
298
                 low = mid + 1;
299
             else if (cmp > 0)
300
                 high = mid - 1;
301
             else
302
                 return mid; // key found
303
         }
304
         return -(low + 1);  // key not found
305
     }

    
Gets the ith element from the given list by repositioning the specified list listIterator. 
310
 
311
     private static <T> T get(ListIterator<? extends T> i, int index) {
312
         T obj = null;
313
         int pos = i.nextIndex();
314
         if (pos <= index) {
315
             do {
316
                 obj = i.next();
317
             } while (pos++ < index);
318
         } else {
319
             do {
320
                 obj = i.previous();
321
             } while (--pos > index);
322
         }
323
         return obj;
324
     }

    
Searches the specified list for the specified object using the binary search algorithm. The list must be sorted into ascending order according to the specified comparator (as by the sort(List, Comparator) method), prior to making this call. If it is not sorted, the results are undefined. If the list contains multiple elements equal to the specified object, there is no guarantee which one will be found.

This method runs in log(n) time for a "random access" list (which provides near-constant-time positional access). If the specified list does not implement the RandomAccess interface and is large, this method will do an iterator-based binary search that performs O(n) link traversals and O(log n) element comparisons.

Parameters:
list the list to be searched.
key the key to be searched for.
c the comparator by which the list is ordered. A null value indicates that the elements' natural ordering should be used.
Returns:
the index of the search key, if it is contained in the list; otherwise, (-(insertion point) - 1). The insertion point is defined as the point at which the key would be inserted into the list: the index of the first element greater than the key, or list.size() if all elements in the list are less than the specified key. Note that this guarantees that the return value will be >= 0 if and only if the key is found.
Throws:
java.lang.ClassCastException if the list contains elements that are not mutually comparable using the specified comparator, or the search key is not mutually comparable with the elements of the list using this comparator.
359
 
360
     public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
361
         if (c==null)
362
             return binarySearch((List) list, key);
363
 
364
         if (list instanceof RandomAccess || list.size()<)
365
             return Collections.indexedBinarySearch(list, key, c);
366
         else
367
             return Collections.iteratorBinarySearch(list, key, c);
368
     }
369
 
370
     private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
371
         int low = 0;
372
         int high = l.size()-1;
373
 
374
         while (low <= high) {
375
             int mid = (low + high) >>> 1;
376
             T midVal = l.get(mid);
377
             int cmp = c.compare(midVal, key);
378
 
379
             if (cmp < 0)
380
                 low = mid + 1;
381
             else if (cmp > 0)
382
                 high = mid - 1;
383
             else
384
                 return mid; // key found
385
         }
386
         return -(low + 1);  // key not found
387
     }
388
 
389
     private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
390
         int low = 0;
391
         int high = l.size()-1;
392
         ListIterator<? extends T> i = l.listIterator();
393
 
394
         while (low <= high) {
395
             int mid = (low + high) >>> 1;
396
             T midVal = get(i, mid);
397
             int cmp = c.compare(midVal, key);
398
 
399
             if (cmp < 0)
400
                 low = mid + 1;
401
             else if (cmp > 0)
402
                 high = mid - 1;
403
             else
404
                 return mid; // key found
405
         }
406
         return -(low + 1);  // key not found
407
     }
408
 
409
     private interface SelfComparable extends Comparable<SelfComparable> {}


    
Reverses the order of the elements in the specified list.

This method runs in linear time.

Parameters:
list the list whose elements are to be reversed.
Throws:
java.lang.UnsupportedOperationException if the specified list or its list-iterator does not support the set operation.
420
 
421
     public static void reverse(List<?> list) {
422
         int size = list.size();
423
         if (size <  || list instanceof RandomAccess) {
424
             for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)
425
                 swap(list, i, j);
426
         } else {
427
             ListIterator fwd = list.listIterator();
428
             ListIterator rev = list.listIterator(size);
429
             for (int i=0, mid=list.size()>>1; i<mid; i++) {
430
                 Object tmp = fwd.next();
431
                 fwd.set(rev.previous());
432
                 rev.set(tmp);
433
             }
434
         }
435
     }

    
Randomly permutes the specified list using a default source of randomness. All permutations occur with approximately equal likelihood.

The hedge "approximately" is used in the foregoing description because default source of randomness is only approximately an unbiased source of independently chosen bits. If it were a perfect source of randomly chosen bits, then the algorithm would choose permutations with perfect uniformity.

This implementation traverses the list backwards, from the last element up to the second, repeatedly swapping a randomly selected element into the "current position". Elements are randomly selected from the portion of the list that runs from the first element to the current position, inclusive.

This method runs in linear time. If the specified list does not implement the RandomAccess interface and is large, this implementation dumps the specified list into an array before shuffling it, and dumps the shuffled array back into the list. This avoids the quadratic behavior that would result from shuffling a "sequential access" list in place.

Parameters:
list the list to be shuffled.
Throws:
java.lang.UnsupportedOperationException if the specified list or its list-iterator does not support the set operation.
464
 
465
     public static void shuffle(List<?> list) {
466
         Random rnd = ;
467
         if (rnd == null)
468
              = rnd = new Random();
469
         shuffle(list, rnd);
470
     }
471
     private static Random r;

    
Randomly permute the specified list using the specified source of randomness. All permutations occur with equal likelihood assuming that the source of randomness is fair.

This implementation traverses the list backwards, from the last element up to the second, repeatedly swapping a randomly selected element into the "current position". Elements are randomly selected from the portion of the list that runs from the first element to the current position, inclusive.

This method runs in linear time. If the specified list does not implement the RandomAccess interface and is large, this implementation dumps the specified list into an array before shuffling it, and dumps the shuffled array back into the list. This avoids the quadratic behavior that would result from shuffling a "sequential access" list in place.

Parameters:
list the list to be shuffled.
rnd the source of randomness to use to shuffle the list.
Throws:
java.lang.UnsupportedOperationException if the specified list or its list-iterator does not support the set operation.
495
 
496
     public static void shuffle(List<?> list, Random rnd) {
497
         int size = list.size();
498
         if (size <  || list instanceof RandomAccess) {
499
             for (int i=size; i>1; i--)
500
                 swap(list, i-1, rnd.nextInt(i));
501
         } else {
502
             Object arr[] = list.toArray();
503
 
504
             // Shuffle array
505
             for (int i=size; i>1; i--)
506
                 swap(arr, i-1, rnd.nextInt(i));
507
 
508
             // Dump array back into list
509
             ListIterator it = list.listIterator();
510
             for (int i=0; i<arr.length; i++) {
511
                 it.next();
512
                 it.set(arr[i]);
513
             }
514
         }
515
     }

    
Swaps the elements at the specified positions in the specified list. (If the specified positions are equal, invoking this method leaves the list unchanged.)

Parameters:
list The list in which to swap elements.
i the index of one element to be swapped.
j the index of the other element to be swapped.
Throws:
java.lang.IndexOutOfBoundsException if either i or j is out of range (i < 0 || i >= list.size() || j < 0 || j >= list.size()).
Since:
1.4
529
 
530
     public static void swap(List<?> list, int i, int j) {
531
         final List l = list;
532
         l.set(i, l.set(j, l.get(i)));
533
     }

    
Swaps the two specified elements in the specified array. 
537
 
538
     private static void swap(Object[] arr, int i, int j) {
539
         Object tmp = arr[i];
540
         arr[i] = arr[j];
541
         arr[j] = tmp;
542
     }

    
Replaces all of the elements of the specified list with the specified element.

This method runs in linear time.

Parameters:
list the list to be filled with the specified element.
obj The element with which to fill the specified list.
Throws:
java.lang.UnsupportedOperationException if the specified list or its list-iterator does not support the set operation.
554
 
555
     public static <T> void fill(List<? super T> list, T obj) {
556
         int size = list.size();
557
 
558
         if (size <  || list instanceof RandomAccess) {
559
             for (int i=0; i<size; i++)
560
                 list.set(i, obj);
561
         } else {
562
             ListIterator<? super T> itr = list.listIterator();
563
             for (int i=0; i<size; i++) {
564
                 itr.next();
565
                 itr.set(obj);
566
             }
567
         }
568
     }

    
Copies all of the elements from one list into another. After the operation, the index of each copied element in the destination list will be identical to its index in the source list. The destination list must be at least as long as the source list. If it is longer, the remaining elements in the destination list are unaffected.

This method runs in linear time.

Parameters:
dest The destination list.
src The source list.
Throws:
java.lang.IndexOutOfBoundsException if the destination list is too small to contain the entire source List.
java.lang.UnsupportedOperationException if the destination list's list-iterator does not support the set operation.
585
 
586
     public static <T> void copy(List<? super T> dest, List<? extends T> src) {
587
         int srcSize = src.size();
588
         if (srcSize > dest.size())
589
             throw new IndexOutOfBoundsException("Source does not fit in dest");
590
 
591
         if (srcSize <  ||
592
             (src instanceof RandomAccess && dest instanceof RandomAccess)) {
593
             for (int i=0; i<srcSize; i++)
594
                 dest.set(i, src.get(i));
595
         } else {
596
             ListIterator<? super T> di=dest.listIterator();
597
             ListIterator<? extends T> si=src.listIterator();
598
             for (int i=0; i<srcSize; i++) {
599
                 di.next();
600
                 di.set(si.next());
601
             }
602
         }
603
     }

    
Returns the minimum element of the given collection, according to the natural ordering of its elements. All elements in the collection must implement the Comparable interface. Furthermore, all elements in the collection must be mutually comparable (that is, e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the collection).

This method iterates over the entire collection, hence it requires time proportional to the size of the collection.

Parameters:
coll the collection whose minimum element is to be determined.
Returns:
the minimum element of the given collection, according to the natural ordering of its elements.
Throws:
java.lang.ClassCastException if the collection contains elements that are not mutually comparable (for example, strings and integers).
NoSuchElementException if the collection is empty.
See also:
java.lang.Comparable
625
 
626
     public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
627
         Iterator<? extends T> i = coll.iterator();
628
         T candidate = i.next();
629
 
630
         while (i.hasNext()) {
631
             T next = i.next();
632
             if (next.compareTo(candidate) < 0)
633
                 candidate = next;
634
         }
635
         return candidate;
636
     }

    
Returns the minimum element of the given collection, according to the order induced by the specified comparator. All elements in the collection must be mutually comparable by the specified comparator (that is, comp.compare(e1, e2) must not throw a ClassCastException for any elements e1 and e2 in the collection).

This method iterates over the entire collection, hence it requires time proportional to the size of the collection.

Parameters:
coll the collection whose minimum element is to be determined.
comp the comparator with which to determine the minimum element. A null value indicates that the elements' natural ordering should be used.
Returns:
the minimum element of the given collection, according to the specified comparator.
Throws:
java.lang.ClassCastException if the collection contains elements that are not mutually comparable using the specified comparator.
NoSuchElementException if the collection is empty.
See also:
java.lang.Comparable
659
 
660
     public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
661
         if (comp==null)
662
             return (T)min((Collection<SelfComparable>) (Collection) coll);
663
 
664
         Iterator<? extends T> i = coll.iterator();
665
         T candidate = i.next();
666
 
667
         while (i.hasNext()) {
668
             T next = i.next();
669
             if (comp.compare(next, candidate) < 0)
670
                 candidate = next;
671
         }
672
         return candidate;
673
     }

    
Returns the maximum element of the given collection, according to the natural ordering of its elements. All elements in the collection must implement the Comparable interface. Furthermore, all elements in the collection must be mutually comparable (that is, e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the collection).

This method iterates over the entire collection, hence it requires time proportional to the size of the collection.

Parameters:
coll the collection whose maximum element is to be determined.
Returns:
the maximum element of the given collection, according to the natural ordering of its elements.
Throws:
java.lang.ClassCastException if the collection contains elements that are not mutually comparable (for example, strings and integers).
NoSuchElementException if the collection is empty.
See also:
java.lang.Comparable
695
 
696
     public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
697
         Iterator<? extends T> i = coll.iterator();
698
         T candidate = i.next();
699
 
700
         while (i.hasNext()) {
701
             T next = i.next();
702
             if (next.compareTo(candidate) > 0)
703
                 candidate = next;
704
         }
705
         return candidate;
706
     }

    
Returns the maximum element of the given collection, according to the order induced by the specified comparator. All elements in the collection must be mutually comparable by the specified comparator (that is, comp.compare(e1, e2) must not throw a ClassCastException for any elements e1 and e2 in the collection).

This method iterates over the entire collection, hence it requires time proportional to the size of the collection.

Parameters:
coll the collection whose maximum element is to be determined.
comp the comparator with which to determine the maximum element. A null value indicates that the elements' natural ordering should be used.
Returns:
the maximum element of the given collection, according to the specified comparator.
Throws:
java.lang.ClassCastException if the collection contains elements that are not mutually comparable using the specified comparator.
NoSuchElementException if the collection is empty.
See also:
java.lang.Comparable
729
 
730
     public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
731
         if (comp==null)
732
             return (T)max((Collection<SelfComparable>) (Collection) coll);
733
 
734
         Iterator<? extends T> i = coll.iterator();
735
         T candidate = i.next();
736
 
737
         while (i.hasNext()) {
738
             T next = i.next();
739
             if (comp.compare(next, candidate) > 0)
740
                 candidate = next;
741
         }
742
         return candidate;
743
     }

    
Rotates the elements in the specified list by the specified distance. After calling this method, the element at index i will be the element previously at index (i - distance) mod list.size(), for all values of i between 0 and list.size()-1, inclusive. (This method has no effect on the size of the list.)

For example, suppose list comprises [t, a, n, k, s]. After invoking Collections.rotate(list, 1) (or Collections.rotate(list, -4)), list will comprise [s, t, a, n, k].

Note that this method can usefully be applied to sublists to move one or more elements within a list while preserving the order of the remaining elements. For example, the following idiom moves the element at index j forward to position k (which must be greater than or equal to j): 

     Collections.rotate(list.subList(j, k+1), -1);
To make this concrete, suppose list comprises [a, b, c, d, e]. To move the element at index 1 (b) forward two positions, perform the following invocation: 
     Collections.rotate(l.subList(1, 4), -1);
The resulting list is [a, c, d, b, e].

To move more than one element forward, increase the absolute value of the rotation distance. To move elements backward, use a positive shift distance.

If the specified list is small or implements the RandomAccess interface, this implementation exchanges the first element into the location it should go, and then repeatedly exchanges the displaced element into the location it should go until a displaced element is swapped into the first element. If necessary, the process is repeated on the second and successive elements, until the rotation is complete. If the specified list is large and doesn't implement the RandomAccess interface, this implementation breaks the list into two sublist views around index -distance mod size. Then the reverse(java.util.List) method is invoked on each sublist view, and finally it is invoked on the entire list. For a more complete description of both algorithms, see Section 2.3 of Jon Bentley's Programming Pearls (Addison-Wesley, 1986).

Parameters:
list the list to be rotated.
distance the distance to rotate the list. There are no constraints on this value; it may be zero, negative, or greater than list.size().
Throws:
java.lang.UnsupportedOperationException if the specified list or its list-iterator does not support the set operation.
Since:
1.4
799
 
800
     public static void rotate(List<?> list, int distance) {
801
         if (list instanceof RandomAccess || list.size() < )
802
             rotate1(list, distance);
803
         else
804
             rotate2(list, distance);
805
     }
806
 
807
     private static <T> void rotate1(List<T> list, int distance) {
808
         int size = list.size();
809
         if (size == 0)
810
             return;
811
         distance = distance % size;
812
         if (distance < 0)
813
             distance += size;
814
         if (distance == 0)
815
             return;
816
 
817
         for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
818
             T displaced = list.get(cycleStart);
819
             int i = cycleStart;
820
             do {
821
                 i += distance;
822
                 if (i >= size)
823
                     i -= size;
824
                 displaced = list.set(i, displaced);
825
                 nMoved ++;
826
             } while (i != cycleStart);
827
         }
828
     }
829
 
830
     private static void rotate2(List<?> list, int distance) {
831
         int size = list.size();
832
         if (size == 0)
833
             return;
834
         int mid =  -distance % size;
835
         if (mid < 0)
836
             mid += size;
837
         if (mid == 0)
838
             return;
839
 
840
         reverse(list.subList(0, mid));
841
         reverse(list.subList(mid, size));
842
         reverse(list);
843
     }

    
Replaces all occurrences of one specified value in a list with another. More formally, replaces with newVal each element e in list such that (oldVal==null ? e==null : oldVal.equals(e)). (This method has no effect on the size of the list.)

Parameters:
list the list in which replacement is to occur.
oldVal the old value to be replaced.
newVal the new value with which oldVal is to be replaced.
Returns:
true if list contained one or more elements e such that (oldVal==null ? e==null : oldVal.equals(e)).
Throws:
java.lang.UnsupportedOperationException if the specified list or its list-iterator does not support the set operation.
Since:
1.4
862
 
863
     public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
864
         boolean result = false;
865
         int size = list.size();
866
         if (size <  || list instanceof RandomAccess) {
867
             if (oldVal==null) {
868
                 for (int i=0; i<size; i++) {
869
                     if (list.get(i)==null) {
870
                         list.set(i, newVal);
871
                         result = true;
872
                     }
873
                 }
874
             } else {
875
                 for (int i=0; i<size; i++) {
876
                     if (oldVal.equals(list.get(i))) {
877
                         list.set(i, newVal);
878
                         result = true;
879
                     }
880
                 }
881
             }
882
         } else {
883
             ListIterator<T> itr=list.listIterator();
884
             if (oldVal==null) {
885
                 for (int i=0; i<size; i++) {
886
                     if (itr.next()==null) {
887
                         itr.set(newVal);
888
                         result = true;
889
                     }
890
                 }
891
             } else {
892
                 for (int i=0; i<size; i++) {
893
                     if (oldVal.equals(itr.next())) {
894
                         itr.set(newVal);
895
                         result = true;
896
                     }
897
                 }
898
             }
899
         }
900
         return result;
901
     }

    
Returns the starting position of the first occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence. More formally, returns the lowest index i such that source.subList(i, i+target.size()).equals(target), or -1 if there is no such index. (Returns -1 if target.size() > source.size().)

This implementation uses the "brute force" technique of scanning over the source list, looking for a match with the target at each location in turn.

Parameters:
source the list in which to search for the first occurrence of target.
target the list to search for as a subList of source.
Returns:
the starting position of the first occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence.
Since:
1.4
922
 
923
     public static int indexOfSubList(List<?> source, List<?> target) {
924
         int sourceSize = source.size();
925
         int targetSize = target.size();
926
         int maxCandidate = sourceSize - targetSize;
927
 
928
         if (sourceSize <  ||
929
             (source instanceof RandomAccess&&target instanceof RandomAccess)) {
930
         nextCand:
931
             for (int candidate = 0; candidate <= maxCandidate; candidate++) {
932
                 for (int i=0, j=candidate; i<targetSize; i++, j++)
933
                     if (!eq(target.get(i), source.get(j)))
934
                         continue nextCand;  // Element mismatch, try next cand
935
                 return candidate;  // All elements of candidate matched target
936
             }
937
         } else {  // Iterator version of above algorithm
938
             ListIterator<?> si = source.listIterator();
939
         nextCand:
940
             for (int candidate = 0; candidate <= maxCandidate; candidate++) {
941
                 ListIterator<?> ti = target.listIterator();
942
                 for (int i=0; i<targetSize; i++) {
943
                     if (!eq(ti.next(), si.next())) {
944
                         // Back up source iterator to next candidate
945
                         for (int j=0; j<i; j++)
946
                             si.previous();
947
                         continue nextCand;
948
                     }
949
                 }
950
                 return candidate;
951
             }
952
         }
953
         return -1;  // No candidate matched the target
954
     }

    
Returns the starting position of the last occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence. More formally, returns the highest index i such that source.subList(i, i+target.size()).equals(target), or -1 if there is no such index. (Returns -1 if target.size() > source.size().)

This implementation uses the "brute force" technique of iterating over the source list, looking for a match with the target at each location in turn.

Parameters:
source the list in which to search for the last occurrence of target.
target the list to search for as a subList of source.
Returns:
the starting position of the last occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence.
Since:
1.4
975
 
976
     public static int lastIndexOfSubList(List<?> source, List<?> target) {
977
         int sourceSize = source.size();
978
         int targetSize = target.size();
979
         int maxCandidate = sourceSize - targetSize;
980
 
981
         if (sourceSize <  ||
982
             source instanceof RandomAccess) {   // Index access version
983
         nextCand:
984
             for (int candidate = maxCandidate; candidate >= 0; candidate--) {
985
                 for (int i=0, j=candidate; i<targetSize; i++, j++)
986
                     if (!eq(target.get(i), source.get(j)))
987
                         continue nextCand;  // Element mismatch, try next cand
988
                 return candidate;  // All elements of candidate matched target
989
             }
990
         } else {  // Iterator version of above algorithm
991
             if (maxCandidate < 0)
992
                 return -1;
993
             ListIterator<?> si = source.listIterator(maxCandidate);
994
         nextCand:
995
             for (int candidate = maxCandidate; candidate >= 0; candidate--) {
996
                 ListIterator<?> ti = target.listIterator();
997
                 for (int i=0; i<targetSize; i++) {
998
                     if (!eq(ti.next(), si.next())) {
999
                         if (candidate != 0) {
1000
                            // Back up source iterator to next candidate
1001
                            for (int j=0; j<=i+1; j++)
1002
                                si.previous();
1003
                        }
1004
                        continue nextCand;
1005
                    }
1006
                }
1007
                return candidate;
1008
            }
1009
        }
1010
        return -1;  // No candidate matched the target
1011
    }
1014
    // Unmodifiable Wrappers
1015

    
Returns an unmodifiable view of the specified collection. This method allows modules to provide users with "read-only" access to internal collections. Query operations on the returned collection "read through" to the specified collection, and attempts to modify the returned collection, whether direct or via its iterator, result in an UnsupportedOperationException.

The returned collection does not pass the hashCode and equals operations through to the backing collection, but relies on Object's equals and hashCode methods. This is necessary to preserve the contracts of these operations in the case that the backing collection is a set or a list.

The returned collection will be serializable if the specified collection is serializable.

Parameters:
c the collection for which an unmodifiable view is to be returned.
Returns:
an unmodifiable view of the specified collection.
1037
    public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
1038
        return new UnmodifiableCollection<>(c);
1039
    }

    

Serial:
include
1044
    static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
1045
        private static final long serialVersionUID = 1820017752578914078L;
1047
        final Collection<? extends E> c;
1049
        UnmodifiableCollection(Collection<? extends E> c) {
1050
            if (c==null)
1051
                throw new NullPointerException();
1052
            this. = c;
1053
        }
1055
        public int size()                   {return .size();}
1056
        public boolean isEmpty()            {return .isEmpty();}
1057
        public boolean contains(Object o)   {return .contains(o);}
1058
        public Object[] toArray()           {return .toArray();}
1059
        public <T> T[] toArray(T[] a)       {return .toArray(a);}
1060
        public String toString()            {return .toString();}
1062
        public Iterator<E> iterator() {
1063
            return new Iterator<E>() {
1064
                private final Iterator<? extends E> i = .iterator();
1066
                public boolean hasNext() {return .hasNext();}
1067
                public E next()          {return .next();}
1068
                public void remove() {
1069
                    throw new UnsupportedOperationException();
1070
                }
1071
            };
1072
        }
1074
        public boolean add(E e) {
1075
            throw new UnsupportedOperationException();
1076
        }
1077
        public boolean remove(Object o) {
1078
            throw new UnsupportedOperationException();
1079
        }
1081
        public boolean containsAll(Collection<?> coll) {
1082
            return .containsAll(coll);
1083
        }
1084
        public boolean addAll(Collection<? extends E> coll) {
1085
            throw new UnsupportedOperationException();
1086
        }
1087
        public boolean removeAll(Collection<?> coll) {
1088
            throw new UnsupportedOperationException();
1089
        }
1090
        public boolean retainAll(Collection<?> coll) {
1091
            throw new UnsupportedOperationException();
1092
        }
1093
        public void clear() {
1094
            throw new UnsupportedOperationException();
1095
        }
1096
    }

    
Returns an unmodifiable view of the specified set. This method allows modules to provide users with "read-only" access to internal sets. Query operations on the returned set "read through" to the specified set, and attempts to modify the returned set, whether direct or via its iterator, result in an UnsupportedOperationException.

The returned set will be serializable if the specified set is serializable.

Parameters:
s the set for which an unmodifiable view is to be returned.
Returns:
an unmodifiable view of the specified set.
1111
    public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
1112
        return new UnmodifiableSet<>(s);
1113
    }

    

Serial:
include
1118
    static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
1119
                                 implements Set<E>, Serializable {
1120
        private static final long serialVersionUID = -9215047833775013803L;
1122
        UnmodifiableSet(Set<? extends E> s)     {super(s);}
1123
        public boolean equals(Object o) {return o == this || .equals(o);}
1124
        public int hashCode()           {return .hashCode();}
1125
    }

    
Returns an unmodifiable view of the specified sorted set. This method allows modules to provide users with "read-only" access to internal sorted sets. Query operations on the returned sorted set "read through" to the specified sorted set. Attempts to modify the returned sorted set, whether direct, via its iterator, or via its subSet, headSet, or tailSet views, result in an UnsupportedOperationException.

The returned sorted set will be serializable if the specified sorted set is serializable.

Parameters:
s the sorted set for which an unmodifiable view is to be returned.
Returns:
an unmodifiable view of the specified sorted set.
1143
    public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
1144
        return new UnmodifiableSortedSet<>(s);
1145
    }

    

Serial:
include
1150
    static class UnmodifiableSortedSet<E>
1151
                             extends UnmodifiableSet<E>
1152
                             implements SortedSet<E>, Serializable {
1153
        private static final long serialVersionUID = -4929149591599911165L;
1154
        private final SortedSet<E> ss;
1156
        UnmodifiableSortedSet(SortedSet<E> s) {super(s);  = s;}
1158
        public Comparator<? super E> comparator() {return .comparator();}
1160
        public SortedSet<E> subSet(E fromElement, E toElement) {
1161
            return new UnmodifiableSortedSet<>(.subSet(fromElement,toElement));
1162
        }
1163
        public SortedSet<E> headSet(E toElement) {
1164
            return new UnmodifiableSortedSet<>(.headSet(toElement));
1165
        }
1166
        public SortedSet<E> tailSet(E fromElement) {
1167
            return new UnmodifiableSortedSet<>(.tailSet(fromElement));
1168
        }
1170
        public E first()                   {return .first();}
1171
        public E last()                    {return .last();}
1172
    }

    
Returns an unmodifiable view of the specified list. This method allows modules to provide users with "read-only" access to internal lists. Query operations on the returned list "read through" to the specified list, and attempts to modify the returned list, whether direct or via its iterator, result in an UnsupportedOperationException.

The returned list will be serializable if the specified list is serializable. Similarly, the returned list will implement RandomAccess if the specified list does.

Parameters:
list the list for which an unmodifiable view is to be returned.
Returns:
an unmodifiable view of the specified list.
1189
    public static <T> List<T> unmodifiableList(List<? extends T> list) {
1190
        return (list instanceof RandomAccess ?
1191
                new UnmodifiableRandomAccessList<>(list) :
1192
                new UnmodifiableList<>(list));
1193
    }

    

Serial:
include
1198
    static class UnmodifiableList<E> extends UnmodifiableCollection<E>
1199
                                  implements List<E> {
1200
        private static final long serialVersionUID = -283967356065247728L;
1201
        final List<? extends E> list;
1203
        UnmodifiableList(List<? extends E> list) {
1204
            super(list);
1205
            this. = list;
1206
        }
1208
        public boolean equals(Object o) {return o == this || .equals(o);}
1209
        public int hashCode()           {return .hashCode();}
1211
        public E get(int index) {return .get(index);}
1212
        public E set(int index, E element) {
1213
            throw new UnsupportedOperationException();
1214
        }
1215
        public void add(int index, E element) {
1216
            throw new UnsupportedOperationException();
1217
        }
1218
        public E remove(int index) {
1219
            throw new UnsupportedOperationException();
1220
        }
1221
        public int indexOf(Object o)            {return .indexOf(o);}
1222
        public int lastIndexOf(Object o)        {return .lastIndexOf(o);}
1223
        public boolean addAll(int index, Collection<? extends E> c) {
1224
            throw new UnsupportedOperationException();
1225
        }
1226
        public ListIterator<E> listIterator()   {return listIterator(0);}
1228
        public ListIterator<E> listIterator(final int index) {
1229
            return new ListIterator<E>() {
1230
                private final ListIterator<? extends E> i
1231
                    = .listIterator(index);
1233
                public boolean hasNext()     {return .hasNext();}
1234
                public E next()              {return .next();}
1235
                public boolean hasPrevious() {return .hasPrevious();}
1236
                public E previous()          {return .previous();}
1237
                public int nextIndex()       {return .nextIndex();}
1238
                public int previousIndex()   {return .previousIndex();}
1240
                public void remove() {
1241
                    throw new UnsupportedOperationException();
1242
                }
1243
                public void set(E e) {
1244
                    throw new UnsupportedOperationException();
1245
                }
1246
                public void add(E e) {
1247
                    throw new UnsupportedOperationException();
1248
                }
1249
            };
1250
        }
1252
        public List<E> subList(int fromIndex, int toIndex) {
1253
            return new UnmodifiableList<>(.subList(fromIndex, toIndex));
1254
        }

        
UnmodifiableRandomAccessList instances are serialized as UnmodifiableList instances to allow them to be deserialized in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). This method inverts the transformation. As a beneficial side-effect, it also grafts the RandomAccess marker onto UnmodifiableList instances that were serialized in pre-1.4 JREs. Note: Unfortunately, UnmodifiableRandomAccessList instances serialized in 1.4.1 and deserialized in 1.4 will become UnmodifiableList instances, as this method was missing in 1.4. 
1268
        private Object readResolve() {
1269
            return ( instanceof RandomAccess
1270
                    ? new UnmodifiableRandomAccessList<>()
1271
                    : this);
1272
        }
1273
    }

    

Serial:
include
1278
    static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E>
1279
                                              implements RandomAccess
1280
    {
1281
        UnmodifiableRandomAccessList(List<? extends E> list) {
1282
            super(list);
1283
        }
1285
        public List<E> subList(int fromIndex, int toIndex) {
1286
            return new UnmodifiableRandomAccessList<>(
1287
                .subList(fromIndex, toIndex));
1288
        }
1290
        private static final long serialVersionUID = -2542308836966382001L;

        
Allows instances to be deserialized in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). UnmodifiableList has a readResolve method that inverts this transformation upon deserialization. 
1298
        private Object writeReplace() {
1299
            return new UnmodifiableList<>();
1300
        }
1301
    }

    
Returns an unmodifiable view of the specified map. This method allows modules to provide users with "read-only" access to internal maps. Query operations on the returned map "read through" to the specified map, and attempts to modify the returned map, whether direct or via its collection views, result in an UnsupportedOperationException.

The returned map will be serializable if the specified map is serializable.

Parameters:
m the map for which an unmodifiable view is to be returned.
Returns:
an unmodifiable view of the specified map.
1317
    public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
1318
        return new UnmodifiableMap<>(m);
1319
    }

    

Serial:
include
1324
    private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
1325
        private static final long serialVersionUID = -1034234728574286014L;
1327
        private final Map<? extends K, ? extends V> m;
1329
        UnmodifiableMap(Map<? extends K, ? extends V> m) {
1330
            if (m==null)
1331
                throw new NullPointerException();
1332
            this. = m;
1333
        }
1335
        public int size()                        {return .size();}
1336
        public boolean isEmpty()                 {return .isEmpty();}
1337
        public boolean containsKey(Object key)   {return .containsKey(key);}
1338
        public boolean containsValue(Object val) {return .containsValue(val);}
1339
        public V get(Object key)                 {return .get(key);}
1341
        public V put(K key, V value) {
1342
            throw new UnsupportedOperationException();
1343
        }
1344
        public V remove(Object key) {
1345
            throw new UnsupportedOperationException();
1346
        }
1347
        public void putAll(Map<? extends K, ? extends V> m) {
1348
            throw new UnsupportedOperationException();
1349
        }
1350
        public void clear() {
1351
            throw new UnsupportedOperationException();
1352
        }
1354
        private transient Set<K> keySet = null;
1355
        private transient Set<Map.Entry<K,V>> entrySet = null;
1356
        private transient Collection<V> values = null;
1358
        public Set<K> keySet() {
1359
            if (==null)
1360
                 = unmodifiableSet(.keySet());
1361
            return ;
1362
        }
1364
        public Set<Map.Entry<K,V>> entrySet() {
1365
            if (==null)
1366
                 = new UnmodifiableEntrySet<>(.entrySet());
1367
            return ;
1368
        }
1370
        public Collection<V> values() {
1371
            if (==null)
1372
                 = unmodifiableCollection(.values());
1373
            return ;
1374
        }
1376
        public boolean equals(Object o) {return o == this || .equals(o);}
1377
        public int hashCode()           {return .hashCode();}
1378
        public String toString()        {return .toString();}

        
We need this class in addition to UnmodifiableSet as Map.Entries themselves permit modification of the backing Map via their setValue operation. This class is subtle: there are many possible attacks that must be thwarted.

Serial:
include
1388
        static class UnmodifiableEntrySet<K,V>
1389
            extends UnmodifiableSet<Map.Entry<K,V>> {
1390
            private static final long serialVersionUID = 7854390611657943733L;
1392
            UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
1393
                super((Set)s);
1394
            }
1395
            public Iterator<Map.Entry<K,V>> iterator() {
1396
                return new Iterator<Map.Entry<K,V>>() {
1397
                    private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = .iterator();
1399
                    public boolean hasNext() {
1400
                        return .hasNext();
1401
                    }
1402
                    public Map.Entry<K,V> next() {
1403
                        return new UnmodifiableEntry<>(.next());
1404
                    }
1405
                    public void remove() {
1406
                        throw new UnsupportedOperationException();
1407
                    }
1408
                };
1409
            }
1411
            public Object[] toArray() {
1412
                Object[] a = .toArray();
1413
                for (int i=0; i<a.length; i++)
1414
                    a[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)a[i]);
1415
                return a;
1416
            }
1418
            public <T> T[] toArray(T[] a) {
1419
                // We don't pass a to c.toArray, to avoid window of
1420
                // vulnerability wherein an unscrupulous multithreaded client
1421
                // could get his hands on raw (unwrapped) Entries from c.
1422
                Object[] arr = .toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
1424
                for (int i=0; i<arr.length; i++)
1425
                    arr[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)arr[i]);
1427
                if (arr.length > a.length)
1428
                    return (T[])arr;
1430
                System.arraycopy(arr, 0, a, 0, arr.length);
1431
                if (a.length > arr.length)
1432
                    a[arr.length] = null;
1433
                return a;
1434
            }

            
This method is overridden to protect the backing set against an object with a nefarious equals function that senses that the equality-candidate is Map.Entry and calls its setValue method. 
1442
            public boolean contains(Object o) {
1443
                if (!(o instanceof Map.Entry))
1444
                    return false;
1445
                return .contains(
1446
                    new UnmodifiableEntry<>((Map.Entry<?,?>) o));
1447
            }

            
The next two methods are overridden to protect against an unscrupulous List whose contains(Object o) method senses when o is a Map.Entry, and calls o.setValue. 
1454
            public boolean containsAll(Collection<?> coll) {
1455
                for (Object e : coll) {
1456
                    if (!contains(e)) // Invokes safe contains() above
1457
                        return false;
1458
                }
1459
                return true;
1460
            }
1461
            public boolean equals(Object o) {
1462
                if (o == this)
1463
                    return true;
1465
                if (!(o instanceof Set))
1466
                    return false;
1467
                Set s = (Set) o;
1468
                if (s.size() != .size())
1469
                    return false;
1470
                return containsAll(s); // Invokes safe containsAll() above
1471
            }

            
This "wrapper class" serves two purposes: it prevents the client from modifying the backing Map, by short-circuiting the setValue method, and it protects the backing Map against an ill-behaved Map.Entry that attempts to modify another Map Entry when asked to perform an equality check. 
1480
            private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> {
1481
                private Map.Entry<? extends K, ? extends V> e;
1483
                UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this. = e;}
1485
                public K getKey()        {return .getKey();}
1486
                public V getValue()      {return .getValue();}
1487
                public V setValue(V value) {
1488
                    throw new UnsupportedOperationException();
1489
                }
1490
                public int hashCode()    {return .hashCode();}
1491
                public boolean equals(Object o) {
1492
                    if (!(o instanceof Map.Entry))
1493
                        return false;
1494
                    Map.Entry t = (Map.Entry)o;
1495
                    return eq(.getKey(),   t.getKey()) &&
1496
                           eq(.getValue(), t.getValue());
1497
                }
1498
                public String toString() {return .toString();}
1499
            }
1500
        }
1501
    }

    
Returns an unmodifiable view of the specified sorted map. This method allows modules to provide users with "read-only" access to internal sorted maps. Query operations on the returned sorted map "read through" to the specified sorted map. Attempts to modify the returned sorted map, whether direct, via its collection views, or via its subMap, headMap, or tailMap views, result in an UnsupportedOperationException.

The returned sorted map will be serializable if the specified sorted map is serializable.

Parameters:
m the sorted map for which an unmodifiable view is to be returned.
Returns:
an unmodifiable view of the specified sorted map.
1519
    public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
1520
        return new UnmodifiableSortedMap<>(m);
1521
    }

    

Serial:
include
1526
    static class UnmodifiableSortedMap<K,V>
1527
          extends UnmodifiableMap<K,V>
1528
          implements SortedMap<K,V>, Serializable {
1529
        private static final long serialVersionUID = -8806743815996713206L;
1531
        private final SortedMap<K, ? extends V> sm;
1533
        UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m);  = m;}
1535
        public Comparator<? super K> comparator() {return .comparator();}
1537
        public SortedMap<K,V> subMap(K fromKey, K toKey) {
1538
            return new UnmodifiableSortedMap<>(.subMap(fromKey, toKey));
1539
        }
1540
        public SortedMap<K,V> headMap(K toKey) {
1541
            return new UnmodifiableSortedMap<>(.headMap(toKey));
1542
        }
1543
        public SortedMap<K,V> tailMap(K fromKey) {
1544
            return new UnmodifiableSortedMap<>(.tailMap(fromKey));
1545
        }
1547
        public K firstKey()           {return .firstKey();}
1548
        public K lastKey()            {return .lastKey();}
1549
    }
1552
    // Synch Wrappers
1553

    
Returns a synchronized (thread-safe) collection backed by the specified collection. In order to guarantee serial access, it is critical that all access to the backing collection is accomplished through the returned collection.

It is imperative that the user manually synchronize on the returned collection when iterating over it: 

  Collection c = Collections.synchronizedCollection(myCollection);
     ...
  synchronized (c) {
      Iterator i = c.iterator(); // Must be in the synchronized block
      while (i.hasNext())
         foo(i.next());
  }
Failure to follow this advice may result in non-deterministic behavior.

The returned collection does not pass the hashCode and equals operations through to the backing collection, but relies on Object's equals and hashCode methods. This is necessary to preserve the contracts of these operations in the case that the backing collection is a set or a list.

The returned collection will be serializable if the specified collection is serializable.

Parameters:
c the collection to be "wrapped" in a synchronized collection.
Returns:
a synchronized view of the specified collection.
1585
    public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
1586
        return new SynchronizedCollection<>(c);
1587
    }
1589
    static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
1590
        return new SynchronizedCollection<>(c, mutex);
1591
    }

    

Serial:
include
1596
    static class SynchronizedCollection<E> implements Collection<E>, Serializable {
1597
        private static final long serialVersionUID = 3053995032091335093L;
1599
        final Collection<E> c;  // Backing Collection
1600
        final Object mutex;     // Object on which to synchronize
1602
        SynchronizedCollection(Collection<E> c) {
1603
            if (c==null)
1604
                throw new NullPointerException();
1605
            this. = c;
1606
             = this;
1607
        }
1608
        SynchronizedCollection(Collection<E> c, Object mutex) {
1609
            this. = c;
1610
            this. = mutex;
1611
        }
1613
        public int size() {
1614
            synchronized () {return .size();}
1615
        }
1616
        public boolean isEmpty() {
1617
            synchronized () {return .isEmpty();}
1618
        }
1619
        public boolean contains(Object o) {
1620
            synchronized () {return .contains(o);}
1621
        }
1622
        public Object[] toArray() {
1623
            synchronized () {return .toArray();}
1624
        }
1625
        public <T> T[] toArray(T[] a) {
1626
            synchronized () {return .toArray(a);}
1627
        }
1629
        public Iterator<E> iterator() {
1630
            return .iterator(); // Must be manually synched by user!
1631
        }
1633
        public boolean add(E e) {
1634
            synchronized () {return .add(e);}
1635
        }
1636
        public boolean remove(Object o) {
1637
            synchronized () {return .remove(o);}
1638
        }
1640
        public boolean containsAll(Collection<?> coll) {
1641
            synchronized () {return .containsAll(coll);}
1642
        }
1643
        public boolean addAll(Collection<? extends E> coll) {
1644
            synchronized () {return .addAll(coll);}
1645
        }
1646
        public boolean removeAll(Collection<?> coll) {
1647
            synchronized () {return .removeAll(coll);}
1648
        }
1649
        public boolean retainAll(Collection<?> coll) {
1650
            synchronized () {return .retainAll(coll);}
1651
        }
1652
        public void clear() {
1653
            synchronized () {.clear();}
1654
        }
1655
        public String toString() {
1656
            synchronized () {return .toString();}
1657
        }
1658
        private void writeObject(ObjectOutputStream s) throws IOException {
1659
            synchronized () {s.defaultWriteObject();}
1660
        }
1661
    }

    
Returns a synchronized (thread-safe) set backed by the specified set. In order to guarantee serial access, it is critical that all access to the backing set is accomplished through the returned set.

It is imperative that the user manually synchronize on the returned set when iterating over it: 

  Set s = Collections.synchronizedSet(new HashSet());
      ...
  synchronized (s) {
      Iterator i = s.iterator(); // Must be in the synchronized block
      while (i.hasNext())
          foo(i.next());
  }
Failure to follow this advice may result in non-deterministic behavior.

The returned set will be serializable if the specified set is serializable.

Parameters:
s the set to be "wrapped" in a synchronized set.
Returns:
a synchronized view of the specified set.
1688
    public static <T> Set<T> synchronizedSet(Set<T> s) {
1689
        return new SynchronizedSet<>(s);
1690
    }
1692
    static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
1693
        return new SynchronizedSet<>(s, mutex);
1694
    }

    

Serial:
include
1699
    static class SynchronizedSet<E>
1700
          extends SynchronizedCollection<E>
1701
          implements Set<E> {
1702
        private static final long serialVersionUID = 487447009682186044L;
1704
        SynchronizedSet(Set<E> s) {
1705
            super(s);
1706
        }
1707
        SynchronizedSet(Set<E> s, Object mutex) {
1708
            super(s, mutex);
1709
        }
1711
        public boolean equals(Object o) {
1712
            synchronized () {return .equals(o);}
1713
        }
1714
        public int hashCode() {
1715
            synchronized () {return .hashCode();}
1716
        }
1717
    }

    
Returns a synchronized (thread-safe) sorted set backed by the specified sorted set. In order to guarantee serial access, it is critical that all access to the backing sorted set is accomplished through the returned sorted set (or its views).

It is imperative that the user manually synchronize on the returned sorted set when iterating over it or any of its subSet, headSet, or tailSet views. 

  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
      ...
  synchronized (s) {
      Iterator i = s.iterator(); // Must be in the synchronized block
      while (i.hasNext())
          foo(i.next());
  }
or: 
  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
  SortedSet s2 = s.headSet(foo);
      ...
  synchronized (s) {  // Note: s, not s2!!!
      Iterator i = s2.iterator(); // Must be in the synchronized block
      while (i.hasNext())
          foo(i.next());
  }
Failure to follow this advice may result in non-deterministic behavior.

The returned sorted set will be serializable if the specified sorted set is serializable.

Parameters:
s the sorted set to be "wrapped" in a synchronized sorted set.
Returns:
a synchronized view of the specified sorted set.
1756
    public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
1757
        return new SynchronizedSortedSet<>(s);
1758
    }

    

Serial:
include
1763
    static class SynchronizedSortedSet<E>
1764
        extends SynchronizedSet<E>
1765
        implements SortedSet<E>
1766
    {
1767
        private static final long serialVersionUID = 8695801310862127406L;
1769
        private final SortedSet<E> ss;
1771
        SynchronizedSortedSet(SortedSet<E> s) {
1772
            super(s);
1773
             = s;
1774
        }
1775
        SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
1776
            super(s, mutex);
1777
             = s;
1778
        }
1780
        public Comparator<? super E> comparator() {
1781
            synchronized () {return .comparator();}
1782
        }
1784
        public SortedSet<E> subSet(E fromElement, E toElement) {
1785
            synchronized () {
1786
                return new SynchronizedSortedSet<>(
1787
                    .subSet(fromElement, toElement), );
1788
            }
1789
        }
1790
        public SortedSet<E> headSet(E toElement) {
1791
            synchronized () {
1792
                return new SynchronizedSortedSet<>(.headSet(toElement), );
1793
            }
1794
        }
1795
        public SortedSet<E> tailSet(E fromElement) {
1796
            synchronized () {
1797
               return new SynchronizedSortedSet<>(.tailSet(fromElement),);
1798
            }
1799
        }
1801
        public E first() {
1802
            synchronized () {return .first();}
1803
        }
1804
        public E last() {
1805
            synchronized () {return .last();}
1806
        }
1807
    }

    
Returns a synchronized (thread-safe) list backed by the specified list. In order to guarantee serial access, it is critical that all access to the backing list is accomplished through the returned list.

It is imperative that the user manually synchronize on the returned list when iterating over it: 

  List list = Collections.synchronizedList(new ArrayList());
      ...
  synchronized (list) {
      Iterator i = list.iterator(); // Must be in synchronized block
      while (i.hasNext())
          foo(i.next());
  }
Failure to follow this advice may result in non-deterministic behavior.

The returned list will be serializable if the specified list is serializable.

Parameters:
list the list to be "wrapped" in a synchronized list.
Returns:
a synchronized view of the specified list.
1834
    public static <T> List<T> synchronizedList(List<T> list) {
1835
        return (list instanceof RandomAccess ?
1836
                new SynchronizedRandomAccessList<>(list) :
1837
                new SynchronizedList<>(list));
1838
    }
1840
    static <T> List<T> synchronizedList(List<T> list, Object mutex) {
1841
        return (list instanceof RandomAccess ?
1842
                new SynchronizedRandomAccessList<>(list, mutex) :
1843
                new SynchronizedList<>(list, mutex));
1844
    }

    

Serial:
include
1849
    static class SynchronizedList<E>
1850
        extends SynchronizedCollection<E>
1851
        implements List<E> {
1852
        private static final long serialVersionUID = -7754090372962971524L;
1854
        final List<E> list;
1856
        SynchronizedList(List<E> list) {
1857
            super(list);
1858
            this. = list;
1859
        }
1860
        SynchronizedList(List<E> list, Object mutex) {
1861
            super(list, mutex);
1862
            this. = list;
1863
        }
1865
        public boolean equals(Object o) {
1866
            synchronized () {return .equals(o);}
1867
        }
1868
        public int hashCode() {
1869
            synchronized () {return .hashCode();}
1870
        }
1872
        public E get(int index) {
1873
            synchronized () {return .get(index);}
1874
        }
1875
        public E set(int index, E element) {
1876
            synchronized () {return .set(index, element);}
1877
        }
1878
        public void add(int index, E element) {
1879
            synchronized () {.add(index, element);}
1880
        }
1881
        public E remove(int index) {
1882
            synchronized () {return .remove(index);}
1883
        }
1885
        public int indexOf(Object o) {
1886
            synchronized () {return .indexOf(o);}
1887
        }
1888
        public int lastIndexOf(Object o) {
1889
            synchronized () {return .lastIndexOf(o);}
1890
        }
1892
        public boolean addAll(int index, Collection<? extends E> c) {
1893
            synchronized () {return .addAll(index, c);}
1894
        }
1896
        public ListIterator<E> listIterator() {
1897
            return .listIterator(); // Must be manually synched by user
1898
        }
1900
        public ListIterator<E> listIterator(int index) {
1901
            return .listIterator(index); // Must be manually synched by user
1902
        }
1904
        public List<E> subList(int fromIndex, int toIndex) {
1905
            synchronized () {
1906
                return new SynchronizedList<>(.subList(fromIndex, toIndex),
1907
                                            );
1908
            }
1909
        }

        
SynchronizedRandomAccessList instances are serialized as SynchronizedList instances to allow them to be deserialized in pre-1.4 JREs (which do not have SynchronizedRandomAccessList). This method inverts the transformation. As a beneficial side-effect, it also grafts the RandomAccess marker onto SynchronizedList instances that were serialized in pre-1.4 JREs. Note: Unfortunately, SynchronizedRandomAccessList instances serialized in 1.4.1 and deserialized in 1.4 will become SynchronizedList instances, as this method was missing in 1.4. 
1923
        private Object readResolve() {
1924
            return ( instanceof RandomAccess
1925
                    ? new SynchronizedRandomAccessList<>()
1926
                    : this);
1927
        }
1928
    }

    

Serial:
include
1933
    static class SynchronizedRandomAccessList<E>
1934
        extends SynchronizedList<E>
1935
        implements RandomAccess {
1937
        SynchronizedRandomAccessList(List<E> list) {
1938
            super(list);
1939
        }
1941
        SynchronizedRandomAccessList(List<E> list, Object mutex) {
1942
            super(list, mutex);
1943
        }
1945
        public List<E> subList(int fromIndex, int toIndex) {
1946
            synchronized () {
1947
                return new SynchronizedRandomAccessList<>(
1948
                    .subList(fromIndex, toIndex), );
1949
            }
1950
        }
1952
        private static final long serialVersionUID = 1530674583602358482L;

        
Allows instances to be deserialized in pre-1.4 JREs (which do not have SynchronizedRandomAccessList). SynchronizedList has a readResolve method that inverts this transformation upon deserialization. 
1960
        private Object writeReplace() {
1961
            return new SynchronizedList<>();
1962
        }
1963
    }

    
Returns a synchronized (thread-safe) map backed by the specified map. In order to guarantee serial access, it is critical that all access to the backing map is accomplished through the returned map.

It is imperative that the user manually synchronize on the returned map when iterating over any of its collection views: 

  Map m = Collections.synchronizedMap(new HashMap());
      ...
  Set s = m.keySet();  // Needn't be in synchronized block
      ...
  synchronized (m) {  // Synchronizing on m, not s!
      Iterator i = s.iterator(); // Must be in synchronized block
      while (i.hasNext())
          foo(i.next());
  }
Failure to follow this advice may result in non-deterministic behavior.

The returned map will be serializable if the specified map is serializable.

Parameters:
m the map to be "wrapped" in a synchronized map.
Returns:
a synchronized view of the specified map.
1992
    public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
1993
        return new SynchronizedMap<>(m);
1994
    }

    

Serial:
include
1999
    private static class SynchronizedMap<K,V>
2000
        implements Map<K,V>, Serializable {
2001
        private static final long serialVersionUID = 1978198479659022715L;
2003
        private final Map<K,V> m;     // Backing Map
2004
        final Object      mutex;        // Object on which to synchronize
2006
        SynchronizedMap(Map<K,V> m) {
2007
            if (m==null)
2008
                throw new NullPointerException();
2009
            this. = m;
2010
             = this;
2011
        }
2013
        SynchronizedMap(Map<K,V> m, Object mutex) {
2014
            this. = m;
2015
            this. = mutex;
2016
        }
2018
        public int size() {
2019
            synchronized () {return .size();}
2020
        }
2021
        public boolean isEmpty() {
2022
            synchronized () {return .isEmpty();}
2023
        }
2024
        public boolean containsKey(Object key) {
2025
            synchronized () {return .containsKey(key);}
2026
        }
2027
        public boolean containsValue(Object value) {
2028
            synchronized () {return .containsValue(value);}
2029
        }
2030
        public V get(Object key) {
2031
            synchronized () {return .get(key);}
2032
        }
2034
        public V put(K key, V value) {
2035
            synchronized () {return .put(key, value);}
2036
        }
2037
        public V remove(Object key) {
2038
            synchronized () {return .remove(key);}
2039
        }
2040
        public void putAll(Map<? extends K, ? extends V> map) {
2041
            synchronized () {.putAll(map);}
2042
        }
2043
        public void clear() {
2044
            synchronized () {.clear();}
2045
        }
2047
        private transient Set<K> keySet = null;
2048
        private transient Set<Map.Entry<K,V>> entrySet = null;
2049
        private transient Collection<V> values = null;
2051
        public Set<K> keySet() {
2052
            synchronized () {
2053
                if (==null)
2054
                     = new SynchronizedSet<>(.keySet(), );
2055
                return ;
2056
            }
2057
        }
2059
        public Set<Map.Entry<K,V>> entrySet() {
2060
            synchronized () {
2061
                if (==null)
2062
                     = new SynchronizedSet<>(.entrySet(), );
2063
                return ;
2064
            }
2065
        }
2067
        public Collection<V> values() {
2068
            synchronized () {
2069
                if (==null)
2070
                     = new SynchronizedCollection<>(.values(), );
2071
                return ;
2072
            }
2073
        }
2075
        public boolean equals(Object o) {
2076
            synchronized () {return .equals(o);}
2077
        }
2078
        public int hashCode() {
2079
            synchronized () {return .hashCode();}
2080
        }
2081
        public String toString() {
2082
            synchronized () {return .toString();}
2083
        }
2084
        private void writeObject(ObjectOutputStream s) throws IOException {
2085
            synchronized () {s.defaultWriteObject();}
2086
        }
2087
    }

    
Returns a synchronized (thread-safe) sorted map backed by the specified sorted map. In order to guarantee serial access, it is critical that all access to the backing sorted map is accomplished through the returned sorted map (or its views).

It is imperative that the user manually synchronize on the returned sorted map when iterating over any of its collection views, or the collections views of any of its subMap, headMap or tailMap views. 

  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
      ...
  Set s = m.keySet();  // Needn't be in synchronized block
      ...
  synchronized (m) {  // Synchronizing on m, not s!
      Iterator i = s.iterator(); // Must be in synchronized block
      while (i.hasNext())
          foo(i.next());
  }
or: 
  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
  SortedMap m2 = m.subMap(foo, bar);
      ...
  Set s2 = m2.keySet();  // Needn't be in synchronized block
      ...
  synchronized (m) {  // Synchronizing on m, not m2 or s2!
      Iterator i = s.iterator(); // Must be in synchronized block
      while (i.hasNext())
          foo(i.next());
  }
Failure to follow this advice may result in non-deterministic behavior.

The returned sorted map will be serializable if the specified sorted map is serializable.

Parameters:
m the sorted map to be "wrapped" in a synchronized sorted map.
Returns:
a synchronized view of the specified sorted map.
2131
    public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
2132
        return new SynchronizedSortedMap<>(m);
2133
    }


    

Serial:
include
2139
    static class SynchronizedSortedMap<K,V>
2140
        extends SynchronizedMap<K,V>
2141
        implements SortedMap<K,V>
2142
    {
2143
        private static final long serialVersionUID = -8798146769416483793L;
2145
        private final SortedMap<K,V> sm;
2147
        SynchronizedSortedMap(SortedMap<K,V> m) {
2148
            super(m);
2149
             = m;
2150
        }
2151
        SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
2152
            super(m, mutex);
2153
             = m;
2154
        }
2156
        public Comparator<? super K> comparator() {
2157
            synchronized () {return .comparator();}
2158
        }
2160
        public SortedMap<K,V> subMap(K fromKey, K toKey) {
2161
            synchronized () {
2162
                return new SynchronizedSortedMap<>(
2163
                    .subMap(fromKey, toKey), );
2164
            }
2165
        }
2166
        public SortedMap<K,V> headMap(K toKey) {
2167
            synchronized () {
2168
                return new SynchronizedSortedMap<>(.headMap(toKey), );
2169
            }
2170
        }
2171
        public SortedMap<K,V> tailMap(K fromKey) {
2172
            synchronized () {
2173
               return new SynchronizedSortedMap<>(.tailMap(fromKey),);
2174
            }
2175
        }
2177
        public K firstKey() {
2178
            synchronized () {return .firstKey();}
2179
        }
2180
        public K lastKey() {
2181
            synchronized () {return .lastKey();}
2182
        }
2183
    }
2185
    // Dynamically typesafe collection wrappers
2186

    
Returns a dynamically typesafe view of the specified collection. Any attempt to insert an element of the wrong type will result in an immediate java.lang.ClassCastException. Assuming a collection contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the collection takes place through the view, it is guaranteed that the collection cannot contain an incorrectly typed element.

The generics mechanism in the language provides compile-time (static) type checking, but it is possible to defeat this mechanism with unchecked casts. Usually this is not a problem, as the compiler issues warnings on all such unchecked operations. There are, however, times when static type checking alone is not sufficient. For example, suppose a collection is passed to a third-party library and it is imperative that the library code not corrupt the collection by inserting an element of the wrong type.

Another use of dynamically typesafe views is debugging. Suppose a program fails with a ClassCastException, indicating that an incorrectly typed element was put into a parameterized collection. Unfortunately, the exception can occur at any time after the erroneous element is inserted, so it typically provides little or no information as to the real source of the problem. If the problem is reproducible, one can quickly determine its source by temporarily modifying the program to wrap the collection with a dynamically typesafe view. For example, this declaration: 

 Collection<String> c = new HashSet<String>();
may be replaced temporarily by this one: 
 Collection<String> c = Collections.checkedCollection(
         new HashSet<String>(), String.class);
Running the program again will cause it to fail at the point where an incorrectly typed element is inserted into the collection, clearly identifying the source of the problem. Once the problem is fixed, the modified declaration may be reverted back to the original.

The returned collection does not pass the hashCode and equals operations through to the backing collection, but relies on Object's equals and hashCode methods. This is necessary to preserve the contracts of these operations in the case that the backing collection is a set or a list.

The returned collection will be serializable if the specified collection is serializable.

Since null is considered to be a value of any reference type, the returned collection permits insertion of null elements whenever the backing collection does.

Parameters:
c the collection for which a dynamically typesafe view is to be returned
type the type of element that c is permitted to hold
Returns:
a dynamically typesafe view of the specified collection
Since:
1.5
2247
    public static <E> Collection<E> checkedCollection(Collection<E> c,
2248
                                                      Class<E> type) {
2249
        return new CheckedCollection<>(c, type);
2250
    }
2252
    @SuppressWarnings("unchecked")
2253
    static <T> T[] zeroLengthArray(Class<T> type) {
2254
        return (T[]) Array.newInstance(type, 0);
2255
    }

    

Serial:
include
2260
    static class CheckedCollection<E> implements Collection<E>, Serializable {
2261
        private static final long serialVersionUID = 1578914078182001775L;
2263
        final Collection<E> c;
2264
        final Class<E> type;
2266
        void typeCheck(Object o) {
2267
            if (o != null && !.isInstance(o))
2268
                throw new ClassCastException(badElementMsg(o));
2269
        }
2271
        private String badElementMsg(Object o) {
2272
            return "Attempt to insert " + o.getClass() +
2273
                " element into collection with element type " + ;
2274
        }
2276
        CheckedCollection(Collection<E> c, Class<E> type) {
2277
            if (c==null || type == null)
2278
                throw new NullPointerException();
2279
            this. = c;
2280
            this. = type;
2281
        }
2283
        public int size()                 { return .size(); }
2284
        public boolean isEmpty()          { return .isEmpty(); }
2285
        public boolean contains(Object o) { return .contains(o); }
2286
        public Object[] toArray()         { return .toArray(); }
2287
        public <T> T[] toArray(T[] a)     { return .toArray(a); }
2288
        public String toString()          { return .toString(); }
2289
        public boolean remove(Object o)   { return .remove(o); }
2290
        public void clear()               {        .clear(); }
2292
        public boolean containsAll(Collection<?> coll) {
2293
            return .containsAll(coll);
2294
        }
2295
        public boolean removeAll(Collection<?> coll) {
2296
            return .removeAll(coll);
2297
        }
2298
        public boolean retainAll(Collection<?> coll) {
2299
            return .retainAll(coll);
2300
        }
2302
        public Iterator<E> iterator() {
2303
            final Iterator<E> it = .iterator();
2304
            return new Iterator<E>() {
2305
                public boolean hasNext() { return it.hasNext(); }
2306
                public E next()          { return it.next(); }
2307
                public void remove()     {        it.remove(); }};
2308
        }
2310
        public boolean add(E e) {
2311
            typeCheck(e);
2312
            return .add(e);
2313
        }
2315
        private E[] zeroLengthElementArray = null; // Lazily initialized
2317
        private E[] zeroLengthElementArray() {
2318
            return  != null ?  :
2319
                ( = zeroLengthArray());
2320
        }
2322
        @SuppressWarnings("unchecked")
2323
        Collection<E> checkedCopyOf(Collection<? extends E> coll) {
2324
            Object[] a = null;
2325
            try {
2326
                E[] z = zeroLengthElementArray();
2327
                a = coll.toArray(z);
2328
                // Defend against coll violating the toArray contract
2329
                if (a.getClass() != z.getClass())
2330
                    a = Arrays.copyOf(a, a.length, z.getClass());
2331
            } catch (ArrayStoreException ignore) {
2332
                // To get better and consistent diagnostics,
2333
                // we call typeCheck explicitly on each element.
2334
                // We call clone() to defend against coll retaining a
2335
                // reference to the returned array and storing a bad
2336
                // element into it after it has been type checked.
2337
                a = coll.toArray().clone();
2338
                for (Object o : a)
2339
                    typeCheck(o);
2340
            }
2341
            // A slight abuse of the type system, but safe here.
2342
            return (Collection<E>) Arrays.asList(a);
2343
        }
2345
        public boolean addAll(Collection<? extends E> coll) {
2346
            // Doing things this way insulates us from concurrent changes
2347
            // in the contents of coll and provides all-or-nothing
2348
            // semantics (which we wouldn't get if we type-checked each
2349
            // element as we added it)
2350
            return .addAll(checkedCopyOf(coll));
2351
        }
2352
    }

    
Returns a dynamically typesafe view of the specified set. Any attempt to insert an element of the wrong type will result in an immediate java.lang.ClassCastException. Assuming a set contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the set takes place through the view, it is guaranteed that the set cannot contain an incorrectly typed element.

A discussion of the use of dynamically typesafe views may be found in the documentation for the checkedCollection method.

The returned set will be serializable if the specified set is serializable.

Since null is considered to be a value of any reference type, the returned set permits insertion of null elements whenever the backing set does.

Parameters:
s the set for which a dynamically typesafe view is to be returned
type the type of element that s is permitted to hold
Returns:
a dynamically typesafe view of the specified set
Since:
1.5
2380
    public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
2381
        return new CheckedSet<>(s, type);
2382
    }

    

Serial:
include
2387
    static class CheckedSet<E> extends CheckedCollection<E>
2388
                                 implements Set<E>, Serializable
2389
    {
2390
        private static final long serialVersionUID = 4694047833775013803L;
2392
        CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
2394
        public boolean equals(Object o) { return o == this || .equals(o); }
2395
        public int hashCode()           { return .hashCode(); }
2396
    }

    
Returns a dynamically typesafe view of the specified sorted set. Any attempt to insert an element of the wrong type will result in an immediate java.lang.ClassCastException. Assuming a sorted set contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the sorted set takes place through the view, it is guaranteed that the sorted set cannot contain an incorrectly typed element.

A discussion of the use of dynamically typesafe views may be found in the documentation for the checkedCollection method.

The returned sorted set will be serializable if the specified sorted set is serializable.

Since null is considered to be a value of any reference type, the returned sorted set permits insertion of null elements whenever the backing sorted set does.

Parameters:
s the sorted set for which a dynamically typesafe view is to be returned
type the type of element that s is permitted to hold
Returns:
a dynamically typesafe view of the specified sorted set
Since:
1.5
2425
    public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
2426
                                                    Class<E> type) {
2427
        return new CheckedSortedSet<>(s, type);
2428
    }

    

Serial:
include
2433
    static class CheckedSortedSet<E> extends CheckedSet<E>
2434
        implements SortedSet<E>, Serializable
2435
    {
2436
        private static final long serialVersionUID = 1599911165492914959L;
2437
        private final SortedSet<E> ss;
2439
        CheckedSortedSet(SortedSet<E> s, Class<E> type) {
2440
            super(s, type);
2441
             = s;
2442
        }
2444
        public Comparator<? super E> comparator() { return .comparator(); }
2445
        public E first()                   { return .first(); }
2446
        public E last()                    { return .last(); }
2448
        public SortedSet<E> subSet(E fromElement, E toElement) {
2449
            return checkedSortedSet(.subSet(fromElement,toElement), );
2450
        }
2451
        public SortedSet<E> headSet(E toElement) {
2452
            return checkedSortedSet(.headSet(toElement), );
2453
        }
2454
        public SortedSet<E> tailSet(E fromElement) {
2455
            return checkedSortedSet(.tailSet(fromElement), );
2456
        }
2457
    }

    
Returns a dynamically typesafe view of the specified list. Any attempt to insert an element of the wrong type will result in an immediate java.lang.ClassCastException. Assuming a list contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the list takes place through the view, it is guaranteed that the list cannot contain an incorrectly typed element.

A discussion of the use of dynamically typesafe views may be found in the documentation for the checkedCollection method.

The returned list will be serializable if the specified list is serializable.

Since null is considered to be a value of any reference type, the returned list permits insertion of null elements whenever the backing list does.

Parameters:
list the list for which a dynamically typesafe view is to be returned
type the type of element that list is permitted to hold
Returns:
a dynamically typesafe view of the specified list
Since:
1.5
2485
    public static <E> List<E> checkedList(List<E> list, Class<E> type) {
2486
        return (list instanceof RandomAccess ?
2487
                new CheckedRandomAccessList<>(list, type) :
2488
                new CheckedList<>(list, type));
2489
    }

    

Serial:
include
2494
    static class CheckedList<E>
2495
        extends CheckedCollection<E>
2496
        implements List<E>
2497
    {
2498
        private static final long serialVersionUID = 65247728283967356L;
2499
        final List<E> list;
2501
        CheckedList(List<E> list, Class<E> type) {
2502
            super(list, type);
2503
            this. = list;
2504
        }
2506
        public boolean equals(Object o)  { return o == this || .equals(o); }
2507
        public int hashCode()            { return .hashCode(); }
2508
        public E get(int index)          { return .get(index); }
2509
        public E remove(int index)       { return .remove(index); }
2510
        public int indexOf(Object o)     { return .indexOf(o); }
2511
        public int lastIndexOf(Object o) { return .lastIndexOf(o); }
2513
        public E set(int index, E element) {
2514
            typeCheck(element);
2515
            return .set(index, element);
2516
        }
2518
        public void add(int index, E element) {
2519
            typeCheck(element);
2520
            .add(index, element);
2521
        }
2523
        public boolean addAll(int index, Collection<? extends E> c) {
2524
            return .addAll(index, checkedCopyOf(c));
2525
        }
2526
        public ListIterator<E> listIterator()   { return listIterator(0); }
2528
        public ListIterator<E> listIterator(final int index) {
2529
            final ListIterator<E> i = .listIterator(index);
2531
            return new ListIterator<E>() {
2532
                public boolean hasNext()     { return i.hasNext(); }
2533
                public E next()              { return i.next(); }
2534
                public boolean hasPrevious() { return i.hasPrevious(); }
2535
                public E previous()          { return i.previous(); }
2536
                public int nextIndex()       { return i.nextIndex(); }
2537
                public int previousIndex()   { return i.previousIndex(); }
2538
                public void remove()         {        i.remove(); }
2540
                public void set(E e) {
2541
                    typeCheck(e);
2542
                    i.set(e);
2543
                }
2545
                public void add(E e) {
2546
                    typeCheck(e);
2547
                    i.add(e);
2548
                }
2549
            };
2550
        }
2552
        public List<E> subList(int fromIndex, int toIndex) {
2553
            return new CheckedList<>(.subList(fromIndex, toIndex), );
2554
        }
2555
    }

    

Serial:
include
2560
    static class CheckedRandomAccessList<E> extends CheckedList<E>
2561
                                            implements RandomAccess
2562
    {
2563
        private static final long serialVersionUID = 1638200125423088369L;
2565
        CheckedRandomAccessList(List<E> list, Class<E> type) {
2566
            super(list, type);
2567
        }
2569
        public List<E> subList(int fromIndex, int toIndex) {
2570
            return new CheckedRandomAccessList<>(
2571
                .subList(fromIndex, toIndex), );
2572
        }
2573
    }

    
Returns a dynamically typesafe view of the specified map. Any attempt to insert a mapping whose key or value have the wrong type will result in an immediate java.lang.ClassCastException. Similarly, any attempt to modify the value currently associated with a key will result in an immediate java.lang.ClassCastException, whether the modification is attempted directly through the map itself, or through a Map.Entry instance obtained from the map's entry set view.

Assuming a map contains no incorrectly typed keys or values prior to the time a dynamically typesafe view is generated, and that all subsequent access to the map takes place through the view (or one of its collection views), it is guaranteed that the map cannot contain an incorrectly typed key or value.

A discussion of the use of dynamically typesafe views may be found in the documentation for the checkedCollection method.

The returned map will be serializable if the specified map is serializable.

Since null is considered to be a value of any reference type, the returned map permits insertion of null keys or values whenever the backing map does.

Parameters:
m the map for which a dynamically typesafe view is to be returned
keyType the type of key that m is permitted to hold
valueType the type of value that m is permitted to hold
Returns:
a dynamically typesafe view of the specified map
Since:
1.5
2609
    public static <K, V> Map<K, V> checkedMap(Map<K, V> m,
2610
                                              Class<K> keyType,
2611
                                              Class<V> valueType) {
2612
        return new CheckedMap<>(m, keyType, valueType);
2613
    }


    

Serial:
include
2619
    private static class CheckedMap<K,V>
2620
        implements Map<K,V>, Serializable
2621
    {
2622
        private static final long serialVersionUID = 5742860141034234728L;
2624
        private final Map<K, V> m;
2625
        final Class<K> keyType;
2626
        final Class<V> valueType;
2628
        private void typeCheck(Object key, Object value) {
2629
            if (key != null && !.isInstance(key))
2630
                throw new ClassCastException(badKeyMsg(key));
2632
            if (value != null && !.isInstance(value))
2633
                throw new ClassCastException(badValueMsg(value));
2634
        }
2636
        private String badKeyMsg(Object key) {
2637
            return "Attempt to insert " + key.getClass() +
2638
                " key into map with key type " + ;
2639
        }
2641
        private String badValueMsg(Object value) {
2642
            return "Attempt to insert " + value.getClass() +
2643
                " value into map with value type " + ;
2644
        }
2646
        CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
2647
            if (m == null || keyType == null || valueType == null)
2648
                throw new NullPointerException();
2649
            this. = m;
2650
            this. = keyType;
2651
            this. = valueType;
2652
        }
2654
        public int size()                      { return .size(); }
2655
        public boolean isEmpty()               { return .isEmpty(); }
2656
        public boolean containsKey(Object key) { return .containsKey(key); }
2657
        public boolean containsValue(Object v) { return .containsValue(v); }
2658
        public V get(Object key)               { return .get(key); }
2659
        public V remove(Object key)            { return .remove(key); }
2660
        public void clear()                    { .clear(); }
2661
        public Set<K> keySet()                 { return .keySet(); }
2662
        public Collection<V> values()          { return .values(); }
2663
        public boolean equals(Object o)        { return o == this || .equals(o); }
2664
        public int hashCode()                  { return .hashCode(); }
2665
        public String toString()               { return .toString(); }
2667
        public V put(K key, V value) {
2668
            typeCheck(key, value);
2669
            return .put(key, value);
2670
        }
2672
        @SuppressWarnings("unchecked")
2673
        public void putAll(Map<? extends K, ? extends V> t) {
2674
            // Satisfy the following goals:
2675
            // - good diagnostics in case of type mismatch
2676
            // - all-or-nothing semantics
2677
            // - protection from malicious t
2678
            // - correct behavior if t is a concurrent map
2679
            Object[] entries = t.entrySet().toArray();
2680
            List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length);
2681
            for (Object o : entries) {
2682
                Map.Entry<?,?> e = (Map.Entry<?,?>) o;
2683
                Object k = e.getKey();
2684
                Object v = e.getValue();
2685
                typeCheck(k, v);
2686
                checked.add(
2687
                    new AbstractMap.SimpleImmutableEntry<>((K) k, (V) v));
2688
            }
2689
            for (Map.Entry<K,V> e : checked)
2690
                .put(e.getKey(), e.getValue());
2691
        }
2693
        private transient Set<Map.Entry<K,V>> entrySet = null;
2695
        public Set<Map.Entry<K,V>> entrySet() {
2696
            if (==null)
2697
                 = new CheckedEntrySet<>(.entrySet(), );
2698
            return ;
2699
        }

        
We need this class in addition to CheckedSet as Map.Entry permits modification of the backing Map via the setValue operation. This class is subtle: there are many possible attacks that must be thwarted.

Serial:
exclude
2709
        static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
2710
            private final Set<Map.Entry<K,V>> s;
2711
            private final Class<V> valueType;
2713
            CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
2714
                this. = s;
2715
                this. = valueType;
2716
            }
2718
            public int size()        { return .size(); }
2719
            public boolean isEmpty() { return .isEmpty(); }
2720
            public String toString() { return .toString(); }
2721
            public int hashCode()    { return .hashCode(); }
2722
            public void clear()      {        .clear(); }
2724
            public boolean add(Map.Entry<K, V> e) {
2725
                throw new UnsupportedOperationException();
2726
            }
2727
            public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
2728
                throw new UnsupportedOperationException();
2729
            }
2731
            public Iterator<Map.Entry<K,V>> iterator() {
2732
                final Iterator<Map.Entry<K, V>> i = .iterator();
2733
                final Class<V> valueType = this.;
2735
                return new Iterator<Map.Entry<K,V>>() {
2736
                    public boolean hasNext() { return i.hasNext(); }
2737
                    public void remove()     { i.remove(); }
2739
                    public Map.Entry<K,V> next() {
2740
                        return checkedEntry(i.next(), valueType);
2741
                    }
2742
                };
2743
            }
2745
            @SuppressWarnings("unchecked")
2746
            public Object[] toArray() {
2747
                Object[] source = .toArray();
2749
                /*
2750
                 * Ensure that we don't get an ArrayStoreException even if
2751
                 * s.toArray returns an array of something other than Object
2752
                 */
2753
                Object[] dest = (CheckedEntry.class.isInstance(
2754
                    source.getClass().getComponentType()) ? source :
2755
                                 new Object[source.length]);
2757
                for (int i = 0; i < source.length; i++)
2758
                    dest[i] = checkedEntry((Map.Entry<K,V>)source[i],
2759
                                           );
2760
                return dest;
2761
            }
2763
            @SuppressWarnings("unchecked")
2764
            public <T> T[] toArray(T[] a) {
2765
                // We don't pass a to s.toArray, to avoid window of
2766
                // vulnerability wherein an unscrupulous multithreaded client
2767
                // could get his hands on raw (unwrapped) Entries from s.
2768
                T[] arr = .toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
2770
                for (int i=0; i<arr.length; i++)
2771
                    arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i],
2772
                                              );
2773
                if (arr.length > a.length)
2774
                    return arr;
2776
                System.arraycopy(arr, 0, a, 0, arr.length);
2777
                if (a.length > arr.length)
2778
                    a[arr.length] = null;
2779
                return a;
2780
            }

            
This method is overridden to protect the backing set against an object with a nefarious equals function that senses that the equality-candidate is Map.Entry and calls its setValue method. 
2788
            public boolean contains(Object o) {
2789
                if (!(o instanceof Map.Entry))
2790
                    return false;
2791
                Map.Entry<?,?> e = (Map.Entry<?,?>) o;
2792
                return .contains(
2793
                    (e instanceof CheckedEntry) ? e : checkedEntry(e, ));
2794
            }

            
The bulk collection methods are overridden to protect against an unscrupulous collection whose contains(Object o) method senses when o is a Map.Entry, and calls o.setValue. 
2801
            public boolean containsAll(Collection<?> c) {
2802
                for (Object o : c)
2803
                    if (!contains(o)) // Invokes safe contains() above
2804
                        return false;
2805
                return true;
2806
            }
2808
            public boolean remove(Object o) {
2809
                if (!(o instanceof Map.Entry))
2810
                    return false;
2811
                return .remove(new AbstractMap.SimpleImmutableEntry
2812
                                <>((Map.Entry<?,?>)o));
2813
            }
2815
            public boolean removeAll(Collection<?> c) {
2816
                return batchRemove(c, false);
2817
            }
2818
            public boolean retainAll(Collection<?> c) {
2819
                return batchRemove(c, true);
2820
            }
2821
            private boolean batchRemove(Collection<?> c, boolean complement) {
2822
                boolean modified = false;
2823
                Iterator<Map.Entry<K,V>> it = iterator();
2824
                while (it.hasNext()) {
2825
                    if (c.contains(it.next()) != complement) {
2826
                        it.remove();
2827
                        modified = true;
2828
                    }
2829
                }
2830
                return modified;
2831
            }
2833
            public boolean equals(Object o) {
2834
                if (o == this)
2835
                    return true;
2836
                if (!(o instanceof Set))
2837
                    return false;
2838
                Set<?> that = (Set<?>) o;
2839
                return that.size() == .size()
2840
                    && containsAll(that); // Invokes safe containsAll() above
2841
            }
2843
            static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e,
2844
                                                            Class<T> valueType) {
2845
                return new CheckedEntry<>(e, valueType);
2846
            }

            
This "wrapper class" serves two purposes: it prevents the client from modifying the backing Map, by short-circuiting the setValue method, and it protects the backing Map against an ill-behaved Map.Entry that attempts to modify another Map.Entry when asked to perform an equality check. 
2855
            private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> {
2856
                private final Map.Entry<K, V> e;
2857
                private final Class<T> valueType;
2859
                CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) {
2860
                    this. = e;
2861
                    this. = valueType;
2862
                }
2864
                public K getKey()        { return .getKey(); }
2865
                public V getValue()      { return .getValue(); }
2866
                public int hashCode()    { return .hashCode(); }
2867
                public String toString() { return .toString(); }
2869
                public V setValue(V value) {
2870
                    if (value != null && !.isInstance(value))
2871
                        throw new ClassCastException(badValueMsg(value));
2872
                    return .setValue(value);
2873
                }
2875
                private String badValueMsg(Object value) {
2876
                    return "Attempt to insert " + value.getClass() +
2877
                        " value into map with value type " + ;
2878
                }
2880
                public boolean equals(Object o) {
2881
                    if (o == this)
2882
                        return true;
2883
                    if (!(o instanceof Map.Entry))
2884
                        return false;
2885
                    return .equals(new AbstractMap.SimpleImmutableEntry
2886
                                    <>((Map.Entry<?,?>)o));
2887
                }
2888
            }
2889
        }
2890
    }

    
Returns a dynamically typesafe view of the specified sorted map. Any attempt to insert a mapping whose key or value have the wrong type will result in an immediate java.lang.ClassCastException. Similarly, any attempt to modify the value currently associated with a key will result in an immediate java.lang.ClassCastException, whether the modification is attempted directly through the map itself, or through a Map.Entry instance obtained from the map's entry set view.

Assuming a map contains no incorrectly typed keys or values prior to the time a dynamically typesafe view is generated, and that all subsequent access to the map takes place through the view (or one of its collection views), it is guaranteed that the map cannot contain an incorrectly typed key or value.

A discussion of the use of dynamically typesafe views may be found in the documentation for the checkedCollection method.

The returned map will be serializable if the specified map is serializable.

Since null is considered to be a value of any reference type, the returned map permits insertion of null keys or values whenever the backing map does.

Parameters:
m the map for which a dynamically typesafe view is to be returned
keyType the type of key that m is permitted to hold
valueType the type of value that m is permitted to hold
Returns:
a dynamically typesafe view of the specified map
Since:
1.5
2926
    public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
2927
                                                        Class<K> keyType,
2928
                                                        Class<V> valueType) {
2929
        return new CheckedSortedMap<>(m, keyType, valueType);
2930
    }

    

Serial:
include
2935
    static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
2936
        implements SortedMap<K,V>, Serializable
2937
    {
2938
        private static final long serialVersionUID = 1599671320688067438L;
2940
        private final SortedMap<K, V> sm;
2942
        CheckedSortedMap(SortedMap<K, V> m,
2943
                         Class<K> keyType, Class<V> valueType) {
2944
            super(m, keyType, valueType);
2945
             = m;
2946
        }
2948
        public Comparator<? super K> comparator() { return .comparator(); }
2949
        public K firstKey()                       { return .firstKey(); }
2950
        public K lastKey()                        { return .lastKey(); }
2952
        public SortedMap<K,V> subMap(K fromKey, K toKey) {
2953
            return checkedSortedMap(.subMap(fromKey, toKey),
2954
                                    , );
2955
        }
2956
        public SortedMap<K,V> headMap(K toKey) {
2957
            return checkedSortedMap(.headMap(toKey), , );
2958
        }
2959
        public SortedMap<K,V> tailMap(K fromKey) {
2960
            return checkedSortedMap(.tailMap(fromKey), , );
2961
        }
2962
    }
2964
    // Empty collections
2965

    
Returns an iterator that has no elements. More precisely,

Implementations of this method are permitted, but not required, to return the same object from multiple invocations.

Returns:
an empty iterator
Since:
1.7
2988
    @SuppressWarnings("unchecked")
2989
    public static <T> Iterator<T> emptyIterator() {
2990
        return (Iterator<T>) .;
2991
    }
2993
    private static class EmptyIterator<E> implements Iterator<E> {
2994
        static final EmptyIterator<Object> EMPTY_ITERATOR
2995
            = new EmptyIterator<>();
2997
        public boolean hasNext() { return false; }
2998
        public E next() { throw new NoSuchElementException(); }
2999
        public void remove() { throw new IllegalStateException(); }
3000
    }

    
Returns a list iterator that has no elements. More precisely,

Implementations of this method are permitted, but not required, to return the same object from multiple invocations.

Returns:
an empty list iterator
Since:
1.7
3034
    @SuppressWarnings("unchecked")
3035
    public static <T> ListIterator<T> emptyListIterator() {
3036
        return (ListIterator<T>) .;
3037
    }
3039
    private static class EmptyListIterator<E>
3040
        extends EmptyIterator<E>
3041
        implements ListIterator<E>
3042
    {
3043
        static final EmptyListIterator<Object> EMPTY_ITERATOR
3044
            = new EmptyListIterator<>();
3046
        public boolean hasPrevious() { return false; }
3047
        public E previous() { throw new NoSuchElementException(); }
3048
        public int nextIndex()     { return 0; }
3049
        public int previousIndex() { return -1; }
3050
        public void set(E e) { throw new IllegalStateException(); }
3051
        public void add(E e) { throw new UnsupportedOperationException(); }
3052
    }

    
Returns an enumeration that has no elements. More precisely,

Implementations of this method are permitted, but not required, to return the same object from multiple invocations.

Returns:
an empty enumeration
Since:
1.7
3073
    @SuppressWarnings("unchecked")
3074
    public static <T> Enumeration<T> emptyEnumeration() {
3075
        return (Enumeration<T>) .;
3076
    }
3078
    private static class EmptyEnumeration<E> implements Enumeration<E> {
3079
        static final EmptyEnumeration<Object> EMPTY_ENUMERATION
3080
            = new EmptyEnumeration<>();
3082
        public boolean hasMoreElements() { return false; }
3083
        public E nextElement() { throw new NoSuchElementException(); }
3084
    }

    
The empty set (immutable). This set is serializable.

See also:
emptySet()
3091
    @SuppressWarnings("unchecked")
3092
    public static final Set EMPTY_SET = new EmptySet<>();

    
Returns the empty set (immutable). This set is serializable. Unlike the like-named field, this method is parameterized.

This example illustrates the type-safe way to obtain an empty set: 

     Set<String> s = Collections.emptySet();
Implementation note: Implementations of this method need not create a separate Set object for each call. Using this method is likely to have comparable cost to using the like-named field. (Unlike this method, the field does not provide type safety.)

Since:
1.5
See also:
EMPTY_SET
3110
    @SuppressWarnings("unchecked")
3111
    public static final <T> Set<T> emptySet() {
3112
        return (Set<T>) ;
3113
    }

    

Serial:
include
3118
    private static class EmptySet<E>
3119
        extends AbstractSet<E>
3120
        implements Serializable
3121
    {
3122
        private static final long serialVersionUID = 1582296315990362920L;
3124
        public Iterator<E> iterator() { return emptyIterator(); }
3126
        public int size() {return 0;}
3127
        public boolean isEmpty() {return true;}
3129
        public boolean contains(Object obj) {return false;}
3130
        public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3132
        public Object[] toArray() { return new Object[0]; }
3134
        public <T> T[] toArray(T[] a) {
3135
            if (a.length > 0)
3136
                a[0] = null;
3137
            return a;
3138
        }
3140
        // Preserves singleton property
3141
        private Object readResolve() {
3142
            return ;
3143
        }
3144
    }

    
The empty list (immutable). This list is serializable.

See also:
emptyList()
3151
    @SuppressWarnings("unchecked")
3152
    public static final List EMPTY_LIST = new EmptyList<>();

    
Returns the empty list (immutable). This list is serializable.

This example illustrates the type-safe way to obtain an empty list: 

     List<String> s = Collections.emptyList();
Implementation note: Implementations of this method need not create a separate List object for each call. Using this method is likely to have comparable cost to using the like-named field. (Unlike this method, the field does not provide type safety.)

Since:
1.5
See also:
EMPTY_LIST
3169
    @SuppressWarnings("unchecked")
3170
    public static final <T> List<T> emptyList() {
3171
        return (List<T>) ;
3172
    }

    

Serial:
include
3177
    private static class EmptyList<E>
3178
        extends AbstractList<E>
3179
        implements RandomAccess, Serializable {
3180
        private static final long serialVersionUID = 8842843931221139166L;
3182
        public Iterator<E> iterator() {
3183
            return emptyIterator();
3184
        }
3185
        public ListIterator<E> listIterator() {
3186
            return emptyListIterator();
3187
        }
3189
        public int size() {return 0;}
3190
        public boolean isEmpty() {return true;}
3192
        public boolean contains(Object obj) {return false;}
3193
        public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3195
        public Object[] toArray() { return new Object[0]; }
3197
        public <T> T[] toArray(T[] a) {
3198
            if (a.length > 0)
3199
                a[0] = null;
3200
            return a;
3201
        }
3203
        public E get(int index) {
3204
            throw new IndexOutOfBoundsException("Index: "+index);
3205
        }
3207
        public boolean equals(Object o) {
3208
            return (o instanceof List) && ((List<?>)o).isEmpty();
3209
        }
3211
        public int hashCode() { return 1; }
3213
        // Preserves singleton property
3214
        private Object readResolve() {
3215
            return ;
3216
        }
3217
    }

    
The empty map (immutable). This map is serializable.

Since:
1.3
See also:
emptyMap()
3225
    @SuppressWarnings("unchecked")
3226
    public static final Map EMPTY_MAP = new EmptyMap<>();

    
Returns the empty map (immutable). This map is serializable.

This example illustrates the type-safe way to obtain an empty set: 

     Map<String, Date> s = Collections.emptyMap();
Implementation note: Implementations of this method need not create a separate Map object for each call. Using this method is likely to have comparable cost to using the like-named field. (Unlike this method, the field does not provide type safety.)

Since:
1.5
See also:
EMPTY_MAP
3243
    @SuppressWarnings("unchecked")
3244
    public static final <K,V> Map<K,V> emptyMap() {
3245
        return (Map<K,V>) ;
3246
    }

    

Serial:
include
3251
    private static class EmptyMap<K,V>
3252
        extends AbstractMap<K,V>
3253
        implements Serializable
3254
    {
3255
        private static final long serialVersionUID = 6428348081105594320L;
3257
        public int size()                          {return 0;}
3258
        public boolean isEmpty()                   {return true;}
3259
        public boolean containsKey(Object key)     {return false;}
3260
        public boolean containsValue(Object value) {return false;}
3261
        public V get(Object key)                   {return null;}
3262
        public Set<K> keySet()                     {return emptySet();}
3263
        public Collection<V> values()              {return emptySet();}
3264
        public Set<Map.Entry<K,V>> entrySet()      {return emptySet();}
3266
        public boolean equals(Object o) {
3267
            return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
3268
        }
3270
        public int hashCode()                      {return 0;}
3272
        // Preserves singleton property
3273
        private Object readResolve() {
3274
            return ;
3275
        }
3276
    }
3278
    // Singleton collections
3279

    
Returns an immutable set containing only the specified object. The returned set is serializable.

Parameters:
o the sole object to be stored in the returned set.
Returns:
an immutable set containing only the specified object.
3287
    public static <T> Set<T> singleton(T o) {
3288
        return new SingletonSet<>(o);
3289
    }
3291
    static <E> Iterator<E> singletonIterator(final E e) {
3292
        return new Iterator<E>() {
3293
            private boolean hasNext = true;
3294
            public boolean hasNext() {
3295
                return ;
3296
            }
3297
            public E next() {
3298
                if () {
3299
                     = false;
3300
                    return e;
3301
                }
3302
                throw new NoSuchElementException();
3303
            }
3304
            public void remove() {
3305
                throw new UnsupportedOperationException();
3306
            }
3307
        };
3308
    }

    

Serial:
include
3313
    private static class SingletonSet<E>
3314
        extends AbstractSet<E>
3315
        implements Serializable
3316
    {
3317
        private static final long serialVersionUID = 3193687207550431679L;
3319
        private final E element;
3321
        SingletonSet(E e) { = e;}
3323
        public Iterator<E> iterator() {
3324
            return singletonIterator();
3325
        }
3327
        public int size() {return 1;}
3329
        public boolean contains(Object o) {return eq(o, );}
3330
    }

    
Returns an immutable list containing only the specified object. The returned list is serializable.

Parameters:
o the sole object to be stored in the returned list.
Returns:
an immutable list containing only the specified object.
Since:
1.3
3340
    public static <T> List<T> singletonList(T o) {
3341
        return new SingletonList<>(o);
3342
    }

    

Serial:
include
3347
    private static class SingletonList<E>
3348
        extends AbstractList<E>
3349
        implements RandomAccess, Serializable {
3351
        private static final long serialVersionUID = 3093736618740652951L;
3353
        private final E element;
3355
        SingletonList(E obj)                { = obj;}
3357
        public Iterator<E> iterator() {
3358
            return singletonIterator();
3359
        }
3361
        public int size()                   {return 1;}
3363
        public boolean contains(Object obj) {return eq(obj, );}
3365
        public E get(int index) {
3366
            if (index != 0)
3367
              throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
3368
            return ;
3369
        }
3370
    }

    
Returns an immutable map, mapping only the specified key to the specified value. The returned map is serializable.

Parameters:
key the sole key to be stored in the returned map.
value the value to which the returned map maps key.
Returns:
an immutable map containing only the specified key-value mapping.
Since:
1.3
3382
    public static <K,V> Map<K,V> singletonMap(K key, V value) {
3383
        return new SingletonMap<>(key, value);
3384
    }

    

Serial:
include
3389
    private static class SingletonMap<K,V>
3390
          extends AbstractMap<K,V>
3391
          implements Serializable {
3392
        private static final long serialVersionUID = -6979724477215052911L;
3394
        private final K k;
3395
        private final V v;
3397
        SingletonMap(K key, V value) {
3398
             = key;
3399
             = value;
3400
        }
3402
        public int size()                          {return 1;}
3404
        public boolean isEmpty()                   {return false;}
3406
        public boolean containsKey(Object key)     {return eq(key, );}
3408
        public boolean containsValue(Object value) {return eq(value, );}
3410
        public V get(Object key)                   {return (eq(key, ) ?  : null);}
3412
        private transient Set<K> keySet = null;
3413
        private transient Set<Map.Entry<K,V>> entrySet = null;
3414
        private transient Collection<V> values = null;
3416
        public Set<K> keySet() {
3417
            if (==null)
3418
                 = singleton();
3419
            return ;
3420
        }
3422
        public Set<Map.Entry<K,V>> entrySet() {
3423
            if (==null)
3424
                 = Collections.<Map.Entry<K,V>>singleton(
3425
                    new SimpleImmutableEntry<>(, ));
3426
            return ;
3427
        }
3429
        public Collection<V> values() {
3430
            if (==null)
3431
                 = singleton();
3432
            return ;
3433
        }
3435
    }
3437
    // Miscellaneous
3438

    
Returns an immutable list consisting of n copies of the specified object. The newly allocated data object is tiny (it contains a single reference to the data object). This method is useful in combination with the List.addAll method to grow lists. The returned list is serializable.

Parameters:
n the number of elements in the returned list.
o the element to appear repeatedly in the returned list.
Returns:
an immutable list consisting of n copies of the specified object.
Throws:
java.lang.IllegalArgumentException if n < 0
See also:
List.addAll(java.util.Collection)
List.addAll(int,java.util.Collection)
3454
    public static <T> List<T> nCopies(int n, T o) {
3455
        if (n < 0)
3456
            throw new IllegalArgumentException("List length = " + n);
3457
        return new CopiesList<>(n, o);
3458
    }

    

Serial:
include
3463
    private static class CopiesList<E>
3464
        extends AbstractList<E>
3465
        implements RandomAccess, Serializable
3466
    {
3467
        private static final long serialVersionUID = 2739099268398711800L;
3469
        final int n;
3470
        final E element;
3472
        CopiesList(int n, E e) {
3473
            assert n >= 0;
3474
            this. = n;
3475
             = e;
3476
        }
3478
        public int size() {
3479
            return ;
3480
        }
3482
        public boolean contains(Object obj) {
3483
            return  != 0 && eq(obj, );
3484
        }
3486
        public int indexOf(Object o) {
3487
            return contains(o) ? 0 : -1;
3488
        }
3490
        public int lastIndexOf(Object o) {
3491
            return contains(o) ?  - 1 : -1;
3492
        }
3494
        public E get(int index) {
3495
            if (index < 0 || index >= )
3496
                throw new IndexOutOfBoundsException("Index: "+index+
3497
                                                    ", Size: "+);
3498
            return ;
3499
        }
3501
        public Object[] toArray() {
3502
            final Object[] a = new Object[];
3503
            if ( != null)
3504
                Arrays.fill(a, 0, , );
3505
            return a;
3506
        }
3508
        public <T> T[] toArray(T[] a) {
3509
            final int n = this.;
3510
            if (a.length < n) {
3511
                a = (T[])java.lang.reflect.Array
3512
                    .newInstance(a.getClass().getComponentType(), n);
3513
                if ( != null)
3514
                    Arrays.fill(a, 0, n, );
3515
            } else {
3516
                Arrays.fill(a, 0, n, );
3517
                if (a.length > n)
3518
                    a[n] = null;
3519
            }
3520
            return a;
3521
        }
3523
        public List<E> subList(int fromIndex, int toIndex) {
3524
            if (fromIndex < 0)
3525
                throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
3526
            if (toIndex > )
3527
                throw new IndexOutOfBoundsException("toIndex = " + toIndex);
3528
            if (fromIndex > toIndex)
3529
                throw new IllegalArgumentException("fromIndex(" + fromIndex +
3530
                                                   ") > toIndex(" + toIndex + ")");
3531
            return new CopiesList<>(toIndex - fromIndex, );
3532
        }
3533
    }

    
Returns a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface. (The natural ordering is the ordering imposed by the objects' own compareTo method.) This enables a simple idiom for sorting (or maintaining) collections (or arrays) of objects that implement the Comparable interface in reverse-natural-order. For example, suppose a is an array of strings. Then: 
          Arrays.sort(a, Collections.reverseOrder());
sorts the array in reverse-lexicographic (alphabetical) order.

The returned comparator is serializable.

Returns:
A comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface.
See also:
java.lang.Comparable
3554
    public static <T> Comparator<T> reverseOrder() {
3555
        return (Comparator<T>) .;
3556
    }

    

Serial:
include
3561
    private static class ReverseComparator
3562
        implements Comparator<Comparable<Object>>, Serializable {
3564
        private static final long serialVersionUID = 7207038068494060240L;
3566
        static final ReverseComparator REVERSE_ORDER
3567
            = new ReverseComparator();
3569
        public int compare(Comparable<Object> c1, Comparable<Object> c2) {
3570
            return c2.compareTo(c1);
3571
        }
3573
        private Object readResolve() { return reverseOrder(); }
3574
    }

    
Returns a comparator that imposes the reverse ordering of the specified comparator. If the specified comparator is null, this method is equivalent to reverseOrder() (in other words, it returns a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface).

The returned comparator is serializable (assuming the specified comparator is also serializable or null).

Parameters:
cmp a comparator who's ordering is to be reversed by the returned comparator or null
Returns:
A comparator that imposes the reverse ordering of the specified comparator.
Since:
1.5
3592
    public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
3593
        if (cmp == null)
3594
            return reverseOrder();
3596
        if (cmp instanceof ReverseComparator2)
3597
            return ((ReverseComparator2<T>)cmp).;
3599
        return new ReverseComparator2<>(cmp);
3600
    }

    

Serial:
include
3605
    private static class ReverseComparator2<T> implements Comparator<T>,
3606
        Serializable
3607
    {
3608
        private static final long serialVersionUID = 4374092139857L;

        
The comparator specified in the static factory. This will never be null, as the static factory returns a ReverseComparator instance if its argument is null.

Serial:
3617
        final Comparator<T> cmp;
3619
        ReverseComparator2(Comparator<T> cmp) {
3620
            assert cmp != null;
3621
            this. = cmp;
3622
        }
3624
        public int compare(T t1, T t2) {
3625
            return .compare(t2, t1);
3626
        }
3628
        public boolean equals(Object o) {
3629
            return (o == this) ||
3630
                (o instanceof ReverseComparator2 &&
3631
                 .equals(((ReverseComparator2)o).));
3632
        }
3634
        public int hashCode() {
3635
            return .hashCode() ^ .;
3636
        }
3637
    }

    
Returns an enumeration over the specified collection. This provides interoperability with legacy APIs that require an enumeration as input.

Parameters:
c the collection for which an enumeration is to be returned.
Returns:
an enumeration over the specified collection.
See also:
Enumeration
3648
    public static <T> Enumeration<T> enumeration(final Collection<T> c) {
3649
        return new Enumeration<T>() {
3650
            private final Iterator<T> i = c.iterator();
3652
            public boolean hasMoreElements() {
3653
                return .hasNext();
3654
            }
3656
            public T nextElement() {
3657
                return .next();
3658
            }
3659
        };
3660
    }

    
Returns an array list containing the elements returned by the specified enumeration in the order they are returned by the enumeration. This method provides interoperability between legacy APIs that return enumerations and new APIs that require collections.

Parameters:
e enumeration providing elements for the returned array list
Returns:
an array list containing the elements returned by the specified enumeration.
Since:
1.4
See also:
Enumeration
ArrayList
3677
    public static <T> ArrayList<T> list(Enumeration<T> e) {
3678
        ArrayList<T> l = new ArrayList<>();
3679
        while (e.hasMoreElements())
3680
            l.add(e.nextElement());
3681
        return l;
3682
    }

    
Returns true if the specified arguments are equal, or both null. 
3687
    static boolean eq(Object o1, Object o2) {
3688
        return o1==null ? o2==null : o1.equals(o2);
3689
    }

    
Returns the number of elements in the specified collection equal to the specified object. More formally, returns the number of elements e in the collection such that (o == null ? e == null : o.equals(e)).

Parameters:
c the collection in which to determine the frequency of o
o the object whose frequency is to be determined
Throws:
java.lang.NullPointerException if c is null
Since:
1.5
3703
    public static int frequency(Collection<?> c, Object o) {
3704
        int result = 0;
3705
        if (o == null) {
3706
            for (Object e : c)
3707
                if (e == null)
3708
                    result++;
3709
        } else {
3710
            for (Object e : c)
3711
                if (o.equals(e))
3712
                    result++;
3713
        }
3714
        return result;
3715
    }

    
Returns true if the two specified collections have no elements in common.

Care must be exercised if this method is used on collections that do not comply with the general contract for Collection. Implementations may elect to iterate over either collection and test for containment in the other collection (or to perform any equivalent computation). If either collection uses a nonstandard equality test (as does a SortedSet whose ordering is not compatible with equals, or the key set of an IdentityHashMap), both collections must use the same nonstandard equality test, or the result of this method is undefined.

Care must also be exercised when using collections that have restrictions on the elements that they may contain. Collection implementations are allowed to throw exceptions for any operation involving elements they deem ineligible. For absolute safety the specified collections should contain only elements which are eligible elements for both collections.

Note that it is permissible to pass the same collection in both parameters, in which case the method will return true if and only if the collection is empty.

Parameters:
c1 a collection
c2 a collection
Returns:
true if the two specified collections have no elements in common.
Throws:
java.lang.NullPointerException if either collection is null.
java.lang.NullPointerException if one collection contains a null element and null is not an eligible element for the other collection. (optional)
java.lang.ClassCastException if one collection contains an element that is of a type which is ineligible for the other collection. (optional)
Since:
1.5
3755
    public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
3756
        // The collection to be used for contains(). Preference is given to
3757
        // the collection who's contains() has lower O() complexity.
3758
        Collection<?> contains = c2;
3759
        // The collection to be iterated. If the collections' contains() impl
3760
        // are of different O() complexity, the collection with slower
3761
        // contains() will be used for iteration. For collections who's
3762
        // contains() are of the same complexity then best performance is
3763
        // achieved by iterating the smaller collection.
3764
        Collection<?> iterate = c1;
3766
        // Performance optimization cases. The heuristics:
3767
        //   1. Generally iterate over c1.
3768
        //   2. If c1 is a Set then iterate over c2.
3769
        //   3. If either collection is empty then result is always true.
3770
        //   4. Iterate over the smaller Collection.
3771
        if (c1 instanceof Set) {
3772
            // Use c1 for contains as a Set's contains() is expected to perform
3773
            // better than O(N/2)
3774
            iterate = c2;
3775
            contains = c1;
3776
        } else if (!(c2 instanceof Set)) {
3777
            // Both are mere Collections. Iterate over smaller collection.
3778
            // Example: If c1 contains 3 elements and c2 contains 50 elements and
3779
            // assuming contains() requires ceiling(N/2) comparisons then
3780
            // checking for all c1 elements in c2 would require 75 comparisons
3781
            // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring
3782
            // 100 comparisons (50 * ceiling(3/2)).
3783
            int c1size = c1.size();
3784
            int c2size = c2.size();
3785
            if (c1size == 0 || c2size == 0) {
3786
                // At least one collection is empty. Nothing will match.
3787
                return true;
3788
            }
3790
            if (c1size > c2size) {
3791
                iterate = c2;
3792
                contains = c1;
3793
            }
3794
        }
3796
        for (Object e : iterate) {
3797
            if (contains.contains(e)) {
3798
               // Found a common element. Collections are not disjoint.
3799
                return false;
3800
            }
3801
        }
3803
        // No common elements were found.
3804
        return true;
3805
    }

    
Adds all of the specified elements to the specified collection. Elements to be added may be specified individually or as an array. The behavior of this convenience method is identical to that of c.addAll(Arrays.asList(elements)), but this method is likely to run significantly faster under most implementations.

When elements are specified individually, this method provides a convenient way to add a few elements to an existing collection: 

     Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");

Parameters:
c the collection into which elements are to be inserted
elements the elements to insert into c
Returns:
true if the collection changed as a result of the call
Throws:
java.lang.UnsupportedOperationException if c does not support the add operation
java.lang.NullPointerException if elements contains one or more null values and c does not permit null elements, or if c or elements are null
java.lang.IllegalArgumentException if some property of a value in elements prevents it from being added to c
Since:
1.5
See also:
Collection.addAll(java.util.Collection)
3834
    public static <T> boolean addAll(Collection<? super T> c, T... elements) {
3835
        boolean result = false;
3836
        for (T element : elements)
3837
            result |= c.add(element);
3838
        return result;
3839
    }

    
Returns a set backed by the specified map. The resulting set displays the same ordering, concurrency, and performance characteristics as the backing map. In essence, this factory method provides a Set implementation corresponding to any Map implementation. There is no need to use this method on a Map implementation that already has a corresponding Set implementation (such as HashMap or TreeMap).

Each method invocation on the set returned by this method results in exactly one method invocation on the backing map or its keySet view, with one exception. The addAll method is implemented as a sequence of put invocations on the backing map.

The specified map must be empty at the time this method is invoked, and should not be accessed directly after this method returns. These conditions are ensured if the map is created empty, passed directly to this method, and no reference to the map is retained, as illustrated in the following code fragment: 

    Set<Object> weakHashSet = Collections.newSetFromMap(
        new WeakHashMap<Object, Boolean>());

Parameters:
map the backing map
Returns:
the set backed by the map
Throws:
java.lang.IllegalArgumentException if map is not empty
Since:
1.6
3870
    public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
3871
        return new SetFromMap<>(map);
3872
    }

    

Serial:
include
3877
    private static class SetFromMap<E> extends AbstractSet<E>
3878
        implements Set<E>, Serializable
3879
    {
3880
        private final Map<E, Boolean> m;  // The backing map
3881
        private transient Set<E> s;       // Its keySet
3883
        SetFromMap(Map<E, Boolean> map) {
3884
            if (!map.isEmpty())
3885
                throw new IllegalArgumentException("Map is non-empty");
3886
             = map;
3887
             = map.keySet();
3888
        }
3890
        public void clear()               {        .clear(); }
3891
        public int size()                 { return .size(); }
3892
        public boolean isEmpty()          { return .isEmpty(); }
3893
        public boolean contains(Object o) { return .containsKey(o); }
3894
        public boolean remove(Object o)   { return .remove(o) != null; }
3895
        public boolean add(E e) { return .put(e, .) == null; }
3896
        public Iterator<E> iterator()     { return .iterator(); }
3897
        public Object[] toArray()         { return .toArray(); }
3898
        public <T> T[] toArray(T[] a)     { return .toArray(a); }
3899
        public String toString()          { return .toString(); }
3900
        public int hashCode()             { return .hashCode(); }
3901
        public boolean equals(Object o)   { return o == this || .equals(o); }
3902
        public boolean containsAll(Collection<?> c) {return .containsAll(c);}
3903
        public boolean removeAll(Collection<?> c)   {return .removeAll(c);}
3904
        public boolean retainAll(Collection<?> c)   {return .retainAll(c);}
3905
        // addAll is the only inherited implementation
3907
        private static final long serialVersionUID = 2454657854757543876L;
3909
        private void readObject(java.io.ObjectInputStream stream)
3910
            throws IOException, ClassNotFoundException
3911
        {
3912
            stream.defaultReadObject();
3913
             = .keySet();
3914
        }
3915
    }

    
Returns a view of a Deque as a Last-in-first-out (Lifo) Queue. Method add is mapped to push, remove is mapped to pop and so on. This view can be useful when you would like to use a method requiring a Queue but you need Lifo ordering.

Each method invocation on the queue returned by this method results in exactly one method invocation on the backing deque, with one exception. The addAll method is implemented as a sequence of addFirst invocations on the backing deque.

Parameters:
deque the deque
Returns:
the queue
Since:
1.6
3934
    public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
3935
        return new AsLIFOQueue<>(deque);
3936
    }

    

Serial:
include
3941
    static class AsLIFOQueue<E> extends AbstractQueue<E>
3942
        implements Queue<E>, Serializable {
3943
        private static final long serialVersionUID = 1802017725587941708L;
3944
        private final Deque<E> q;
3945
        AsLIFOQueue(Deque<E> q)           { this. = q; }
3946
        public boolean add(E e)           { .addFirst(e); return true; }
3947
        public boolean offer(E e)         { return .offerFirst(e); }
3948
        public E poll()                   { return .pollFirst(); }
3949
        public E remove()                 { return .removeFirst(); }
3950
        public E peek()                   { return .peekFirst(); }
3951
        public E element()                { return .getFirst(); }
3952
        public void clear()               {        .clear(); }
3953
        public int size()                 { return .size(); }
3954
        public boolean isEmpty()          { return .isEmpty(); }
3955
        public boolean contains(Object o) { return .contains(o); }
3956
        public boolean remove(Object o)   { return .remove(o); }
3957
        public Iterator<E> iterator()     { return .iterator(); }
3958
        public Object[] toArray()         { return .toArray(); }
3959
        public <T> T[] toArray(T[] a)     { return .toArray(a); }
3960
        public String toString()          { return .toString(); }
3961
        public boolean containsAll(Collection<?> c) {return .containsAll(c);}
3962
        public boolean removeAll(Collection<?> c)   {return .removeAll(c);}
3963
        public boolean retainAll(Collection<?> c)   {return .retainAll(c);}
3964
        // We use inherited addAll; forwarding addAll would be wrong
3965
    }
New to GrepCode? Check out our FAQ X