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1. What is a good 64bit hash function in Java for textual strings?
I'm looking for a hash function that: Hashes textual strings well (e.g. few collisions) Is written in Java, and widely used Bonus: works on several fields (instead of me concatenating them and applying the hash on the concatenated string) Bonus: Has a 128-bit variant. Bonus: Not CPU intensive.
2. What is the Java equivalent of .NET BitConverter?
I was writing an article in which I wanted to show how to send objects across the network, from Java to CLR/.Net and Back. http://ferozedaud.blogspot.com/2009/11/howto-serialize-data-from-object-from.html While doing research for this, I could not find a Java equivalent for BitConverter class that exists in .NET. Due to this, I had to resort to using ByteBuffer to marshal primitive types to b...
3. Store Numbers as Binary in files
I have numbers written as ASCII codes in my file. For example "9" is stored as two bytes 57 i.e. 8 bits in total. I want to optimize storage by just storing those numbers as binary values for example numbers from 0-9 to be stored using 4 bits only. Any help?!
4. Convert int to unsigned short java
I have written a .obj parser in java to modelize 3D objects on iPhone. I would like to export the data as a binary file, which must be as small as possible. I have plenty of indices that would fit a unsigned short, but they are represented as int in java. I would like to use the ByteBuffer class to do the conversion just before writing the data in a file. I suppose I will have to manipulate b...
5. How do I convert Long to byte[] and back in java
How do I convert a long to a byte[] and back in Java? I'm trying convert a long to a byte[] so that I will be able to send the byte[] over a tcp connection. On the other side I want to take that byte[] and convert it back into a double. Any tips would be appreciated.
6. Convert long to byte array and add it to another array
I want to change a values in byte array to put a long timestamp value in in the MSBs. Can someone tell me whats the best way to do it. I do not want to insert values bit-by-bit which I believe is very inefficient. long time = System.currentTimeMillis(); Long timeStamp = new Long(time); byte[] bArray = new byte[128]; What I want is something like: byte[0-63] = timeStamp.byteValue(); Is s...
7. Byte order java/.net
When sending information from a java application to a C# application through sockets, is the byte order different? Or can I just send an integer from C# to a java application and read it as integer? (And do the OS matter, or is the same for java/.net no matter how the actual OS handles it?)
8. How to convert a Java Long to byte[] for Cassandra?
Lazy programmer alert. :) Cassandra stores column values as bytes (Java example). Specifying a LongType comparator compares those bytes as a long. I want the value of a long into a Cassandra-friendly byte[]. How? I poked around for awhile. I think you people can help me faster. EDIT: Both Alexander and Eli's answers agreed with this reverse transformation. Thanks!
9. Network Order short (Java)
I need to send a Network Order short for a game server I'm writing using Java. I read about network order, but I couldn't find any details about a short that is sent before the data. Could someone explain to me what it is, and how to send one to a client with Java?
10. (Java) Write decimal/hex to a file, and not string
If I have a file, and I want to literally write '42' to it (the value, not the string), which for example is 2a in hex, how do I do it? I want to be able to use something like outfile.write(42) or outfile.write(2a) and not write the string to the file. (I realize this is a simple question but I can't find the answer of google, probably because I don't know the correct search terms)
11. Converting any object to a byte array in java
I have an object of type X which I want to convert into byte array before sending it to store in S3. Can anybody tell me how to do this? I appreciate your help.
12. Creating and writing file from a FileOutputStream in Java
Okay, so I'm working on a project where I use a Java program to initiate a socket connection between two classes (a FileSender and FileReceiver). My basic idea was that the FileSender would look like this: try { writer = new DataOutputStream(connect.getOutputStream()); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } //While we have bytes to send whi...
13. Bittorrent Peer Wire Protocol implementing in Java
I have a couple of questions regarding the Bittorrent Peer Wire Protocol. I am trying to implement it in Java using this spec. In Peer Wire Protocol section it says that all integers are four byte big endian values. AFAIK java uses big endian. Does that mean say if i want to send a choke message choke:<len=0001><id=0> Do i just write to the sokcet 1 followed by 0? As for my seco...
14. Sending int through socket in Java
What is the best possible way to send an int through a socket in Java? Right now I'm looking at sockout.write((byte)( length >> 24 )); sockout.write((byte)( (length << 8) >> 24 )); sockout.write((byte)( (length << 16) >> 24 )); sockout.write((byte)( (length << 24) >> 24 )); and then trying to rebuild the int from bytes on the other side, but it does...
15. How do I truncate a java integer to fit/exand to a given number of bytes?
I am designing an archive format(Just for fun) in Java using this template- First 4 bytes: Number of files in the archive Next 4 bytes: Number of bytes in the filename Next N bytes: Filename Next 10 bytes: Number of bytes in the file Next N bytes: File contents from PHP Safe way to download mutliple files and save them. I am having on trouble with finding the values of the number of files e...
16. C++ FILE readInt function? (from a binary file)
Is there a function for FILE (fopen?) that allows me to just read one int from a binary file? So far I'm trying this, but I'm getting some kind of error I can't see cause the program just crashes without telling me. void opentest() { FILE *fp = fopen("dqmapt.mp", "r"); int i = 0; int j = 0; int k = 0; int * buffer; if (fp) { buffer = (int *) (sizeof(int)); ...
17. Object attributes to same-length representation for faster reading
I want to convert the attributes of my 'person' object to a representation where I can write lines to a file representing each person. A number of machines need to concurrently read their allocated chunk of the file and so I am moving from lines of character encoded text to list of bytes instead. I hope that by each person's representation being the same length I don't have to read every charac...
18. Possible to send an image to my Servlet as a ByteBuffer?
I am attempting to have my android phone connect to my servlet and send it a certain image. The way I figured I would do this, is to use the copyPixelsToBuffer() function and then attempt to send this to the servlet through some output stream(similar to how I would do it in a normal stand alone java application). Will this way work? If so, what kind of stream do I use exactly? Should I just use...
19. Java BitSet - wrapper to put chars/Strings in
I'm making use of BitSet in Java to store values I have to serialize and deserialize into/from lower abstraction levels. This is to create a file-format container. Currently I want to store a String into a BitSet: private BitSet string_to_bit(String content_string) { BitSet result = new BitSet(this.size); char[] content_string_arr = new char[content_string.length()]; ...
20. Socket connection from Java to Objective-C
I'm implementing a server push via a socket connection to an Objective-C based application. I'm at the point where I'm sending my data through an outputstream on the socket but I need to reassemble the data on the Objective-c end. At this point I haven't even looked at the objective-c IO classes and I am wondering how can I ensure maximum compatibility on the java end? I'm guessing I have to st...
21. How to output binary data to a file in Java?
I'm trying to write data to a file in binary format for compression. The data consists entirely of floating points so I decided to quantize the data to an intergers between 0 and 65535 so the data can be written as two bit unsigned integers and ultimately save space. However, I need to output that quantized data to a file in binary instead of human-readable Ascii. At the moment this is what I'... 
1
  /*
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   * Copyright 1994-2004 Sun Microsystems, Inc.  All Rights Reserved.
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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   *
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   * This code is free software; you can redistribute it and/or modify it
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   * under the terms of the GNU General Public License version 2 only, as
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   * published by the Free Software Foundation.  Sun designates this
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   * particular file as subject to the "Classpath" exception as provided
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   * by Sun in the LICENSE file that accompanied this code.
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  *
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  * This code is distributed in the hope that it will be useful, but WITHOUT
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  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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  * version 2 for more details (a copy is included in the LICENSE file that
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  * accompanied this code).
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  *
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  * You should have received a copy of the GNU General Public License version
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  * 2 along with this work; if not, write to the Free Software Foundation,
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  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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  *
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  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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  * CA 95054 USA or visit www.sun.com if you need additional information or
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  * have any questions.
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  */
25
 
26
 package java.io;

A data output stream lets an application write primitive Java data types to an output stream in a portable way. An application can then use a data input stream to read the data back in.

Author(s):
unascribed
Since:
JDK1.0
See also:
DataInputStream
36
 
37
 public
38
 class DataOutputStream extends FilterOutputStream implements DataOutput {
    
The number of bytes written to the data output stream so far. If this counter overflows, it will be wrapped to Integer.MAX_VALUE. 
42
 
43
     protected int written;

    
bytearr is initialized on demand by writeUTF 
47
 
48
     private byte[] bytearr = null;

    
Creates a new data output stream to write data to the specified underlying output stream. The counter written is set to zero.

Parameters:
out the underlying output stream, to be saved for later use.
See also:
FilterOutputStream.out
58
 
59
     public DataOutputStream(OutputStream out) {
60
         super(out);
61
     }

    
Increases the written counter by the specified value until it reaches Integer.MAX_VALUE. 
66
 
67
     private void incCount(int value) {
68
         int temp =  + value;
69
         if (temp < 0) {
70
             temp = .;
71
         }
72
          = temp;
73
     }

    
Writes the specified byte (the low eight bits of the argument b) to the underlying output stream. If no exception is thrown, the counter written is incremented by 1.

Implements the write method of OutputStream.

Parameters:
b the byte to be written.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
86
 
87
     public synchronized void write(int b) throws IOException {
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         .write(b);
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         incCount(1);
90
     }

    
Writes len bytes from the specified byte array starting at offset off to the underlying output stream. If no exception is thrown, the counter written is incremented by len.

Parameters:
b the data.
off the start offset in the data.
len the number of bytes to write.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
104
    public synchronized void write(byte b[], int off, int len)
105
        throws IOException
106
    {
107
        .write(b, off, len);
108
        incCount(len);
109
    }

    
Flushes this data output stream. This forces any buffered output bytes to be written out to the stream.

The flush method of DataOutputStream calls the flush method of its underlying output stream.

Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
OutputStream.flush()
122
    public void flush() throws IOException {
123
        .flush();
124
    }

    
Writes a boolean to the underlying output stream as a 1-byte value. The value true is written out as the value (byte)1; the value false is written out as the value (byte)0. If no exception is thrown, the counter written is incremented by 1.

Parameters:
v a boolean value to be written.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
138
    public final void writeBoolean(boolean v) throws IOException {
139
        .write(v ? 1 : 0);
140
        incCount(1);
141
    }

    
Writes out a byte to the underlying output stream as a 1-byte value. If no exception is thrown, the counter written is incremented by 1.

Parameters:
v a byte value to be written.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
152
    public final void writeByte(int v) throws IOException {
153
        .write(v);
154
        incCount(1);
155
    }

    
Writes a short to the underlying output stream as two bytes, high byte first. If no exception is thrown, the counter written is incremented by 2.

Parameters:
v a short to be written.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
166
    public final void writeShort(int v) throws IOException {
167
        .write((v >>> 8) & 0xFF);
168
        .write((v >>> 0) & 0xFF);
169
        incCount(2);
170
    }

    
Writes a char to the underlying output stream as a 2-byte value, high byte first. If no exception is thrown, the counter written is incremented by 2.

Parameters:
v a char value to be written.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
181
    public final void writeChar(int v) throws IOException {
182
        .write((v >>> 8) & 0xFF);
183
        .write((v >>> 0) & 0xFF);
184
        incCount(2);
185
    }

    
Writes an int to the underlying output stream as four bytes, high byte first. If no exception is thrown, the counter written is incremented by 4.

Parameters:
v an int to be written.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
196
    public final void writeInt(int v) throws IOException {
197
        .write((v >>> 24) & 0xFF);
198
        .write((v >>> 16) & 0xFF);
199
        .write((v >>>  8) & 0xFF);
200
        .write((v >>>  0) & 0xFF);
201
        incCount(4);
202
    }
204
    private byte writeBuffer[] = new byte[8];

    
Writes a long to the underlying output stream as eight bytes, high byte first. In no exception is thrown, the counter written is incremented by 8.

Parameters:
v a long to be written.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
215
    public final void writeLong(long v) throws IOException {
216
        [0] = (byte)(v >>> 56);
217
        [1] = (byte)(v >>> 48);
218
        [2] = (byte)(v >>> 40);
219
        [3] = (byte)(v >>> 32);
220
        [4] = (byte)(v >>> 24);
221
        [5] = (byte)(v >>> 16);
222
        [6] = (byte)(v >>>  8);
223
        [7] = (byte)(v >>>  0);
224
        .write(, 0, 8);
225
        incCount(8);
226
    }

    
Converts the float argument to an int using the floatToIntBits method in class Float, and then writes that int value to the underlying output stream as a 4-byte quantity, high byte first. If no exception is thrown, the counter written is incremented by 4.

Parameters:
v a float value to be written.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
java.lang.Float.floatToIntBits(float)
241
    public final void writeFloat(float v) throws IOException {
242
        writeInt(Float.floatToIntBits(v));
243
    }

    
Converts the double argument to a long using the doubleToLongBits method in class Double, and then writes that long value to the underlying output stream as an 8-byte quantity, high byte first. If no exception is thrown, the counter written is incremented by 8.

Parameters:
v a double value to be written.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
java.lang.Double.doubleToLongBits(double)
258
    public final void writeDouble(double v) throws IOException {
259
        writeLong(Double.doubleToLongBits(v));
260
    }

    
Writes out the string to the underlying output stream as a sequence of bytes. Each character in the string is written out, in sequence, by discarding its high eight bits. If no exception is thrown, the counter written is incremented by the length of s.

Parameters:
s a string of bytes to be written.
Throws:
IOException if an I/O error occurs.
See also:
FilterOutputStream.out
273
    public final void writeBytes(String s) throws IOException {
274
        int len = s.length();
275
        for (int i = 0 ; i < len ; i++) {
276
            .write((byte)s.charAt(i));
277
        }
278
        incCount(len);
279
    }

    
Writes a string to the underlying output stream as a sequence of characters. Each character is written to the data output stream as if by the writeChar method. If no exception is thrown, the counter written is incremented by twice the length of s.

Parameters:
s a String value to be written.
Throws:
IOException if an I/O error occurs.
See also:
writeChar(int)
FilterOutputStream.out
293
    public final void writeChars(String s) throws IOException {
294
        int len = s.length();
295
        for (int i = 0 ; i < len ; i++) {
296
            int v = s.charAt(i);
297
            .write((v >>> 8) & 0xFF);
298
            .write((v >>> 0) & 0xFF);
299
        }
300
        incCount(len * 2);
301
    }

    
Writes a string to the underlying output stream using modified UTF-8 encoding in a machine-independent manner.

First, two bytes are written to the output stream as if by the writeShort method giving the number of bytes to follow. This value is the number of bytes actually written out, not the length of the string. Following the length, each character of the string is output, in sequence, using the modified UTF-8 encoding for the character. If no exception is thrown, the counter written is incremented by the total number of bytes written to the output stream. This will be at least two plus the length of str, and at most two plus thrice the length of str.

Parameters:
str a string to be written.
Throws:
IOException if an I/O error occurs.
322
    public final void writeUTF(String str) throws IOException {
323
        writeUTF(str, this);
324
    }

    
Writes a string to the specified DataOutput using modified UTF-8 encoding in a machine-independent manner.

First, two bytes are written to out as if by the writeShort method giving the number of bytes to follow. This value is the number of bytes actually written out, not the length of the string. Following the length, each character of the string is output, in sequence, using the modified UTF-8 encoding for the character. If no exception is thrown, the counter written is incremented by the total number of bytes written to the output stream. This will be at least two plus the length of str, and at most two plus thrice the length of str.

Parameters:
str a string to be written.
out destination to write to
Returns:
The number of bytes written out.
Throws:
IOException if an I/O error occurs.
346
    static int writeUTF(String str, DataOutput out) throws IOException {
347
        int strlen = str.length();
348
        int utflen = 0;
349
        int c, count = 0;
351
        /* use charAt instead of copying String to char array */
352
        for (int i = 0; i < strlen; i++) {
353
            c = str.charAt(i);
354
            if ((c >= 0x0001) && (c <= 0x007F)) {
355
                utflen++;
356
            } else if (c > 0x07FF) {
357
                utflen += 3;
358
            } else {
359
                utflen += 2;
360
            }
361
        }
363
        if (utflen > 65535)
364
            throw new UTFDataFormatException(
365
                "encoded string too long: " + utflen + " bytes");
367
        byte[] bytearr = null;
368
        if (out instanceof DataOutputStream) {
369
            DataOutputStream dos = (DataOutputStream)out;
370
            if(dos.bytearr == null || (dos.bytearr.length < (utflen+2)))
371
                dos.bytearr = new byte[(utflen*2) + 2];
372
            bytearr = dos.bytearr;
373
        } else {
374
            bytearr = new byte[utflen+2];
375
        }
377
        bytearr[count++] = (byte) ((utflen >>> 8) & 0xFF);
378
        bytearr[count++] = (byte) ((utflen >>> 0) & 0xFF);
380
        int i=0;
381
        for (i=0; i<strlen; i++) {
382
           c = str.charAt(i);
383
           if (!((c >= 0x0001) && (c <= 0x007F))) break;
384
           bytearr[count++] = (byte) c;
385
        }
387
        for (;i < strlen; i++){
388
            c = str.charAt(i);
389
            if ((c >= 0x0001) && (c <= 0x007F)) {
390
                bytearr[count++] = (byte) c;
392
            } else if (c > 0x07FF) {
393
                bytearr[count++] = (byte) (0xE0 | ((c >> 12) & 0x0F));
394
                bytearr[count++] = (byte) (0x80 | ((c >>  6) & 0x3F));
395
                bytearr[count++] = (byte) (0x80 | ((c >>  0) & 0x3F));
396
            } else {
397
                bytearr[count++] = (byte) (0xC0 | ((c >>  6) & 0x1F));
398
                bytearr[count++] = (byte) (0x80 | ((c >>  0) & 0x3F));
399
            }
400
        }
401
        out.write(bytearr, 0, utflen+2);
402
        return utflen + 2;
403
    }

    
Returns the current value of the counter written, the number of bytes written to this data output stream so far. If the counter overflows, it will be wrapped to Integer.MAX_VALUE.

Returns:
the value of the written field.
See also:
written
413
    public final int size() {
414
        return ;
415
    }
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