The
Collator class performs locale-sensitive
String comparison. You use this class to build
searching and sorting routines for natural language text.
Collator is an abstract base class. Subclasses
implement specific collation strategies. One subclass,
RuleBasedCollator, is currently provided with
the Java Platform and is applicable to a wide set of languages. Other
subclasses may be created to handle more specialized needs.
Like other locale-sensitive classes, you can use the static
factory method, getInstance, to obtain the appropriate
Collator object for a given locale. You will only need
to look at the subclasses of Collator if you need
to understand the details of a particular collation strategy or
if you need to modify that strategy.
The following example shows how to compare two strings using
the Collator for the default locale.
// Compare two strings in the default locale
Collator myCollator = Collator.getInstance();
if( myCollator.compare("abc", "ABC") < 0 )
System.out.println("abc is less than ABC");
else
System.out.println("abc is greater than or equal to ABC");
You can set a Collator's strength property
to determine the level of difference considered significant in
comparisons. Four strengths are provided: PRIMARY,
SECONDARY, TERTIARY, and IDENTICAL.
The exact assignment of strengths to language features is
locale dependant. For example, in Czech, "e" and "f" are considered
primary differences, while "e" and "ě" are secondary differences,
"e" and "E" are tertiary differences and "e" and "e" are identical.
The following shows how both case and accents could be ignored for
US English.
//Get the Collator for US English and set its strength to PRIMARY
Collator usCollator = Collator.getInstance(Locale.US);
usCollator.setStrength(Collator.PRIMARY);
if( usCollator.compare("abc", "ABC") == 0 ) {
System.out.println("Strings are equivalent");
}
For comparing Strings exactly once, the compare
method provides the best performance. When sorting a list of
Strings however, it is generally necessary to compare each
String multiple times. In this case, CollationKeys
provide better performance. The CollationKey class converts
a String to a series of bits that can be compared bitwise
against other CollationKeys. A CollationKey is
created by a Collator object for a given String.
Note: CollationKeys from different
Collators can not be compared. See the class description
for CollationKeyCollationKeys.
Collator strength value. When set, only PRIMARY differences are
considered significant during comparison. The assignment of strengths
to language features is locale dependant. A common example is for
different base letters ("a" vs "b") to be considered a PRIMARY difference.
public final static int PRIMARY = 0;
Collator strength value. When set, only SECONDARY and above differences are
considered significant during comparison. The assignment of strengths
to language features is locale dependant. A common example is for
different accented forms of the same base letter ("a" vs "\u00E4") to be
considered a SECONDARY difference.
Collator strength value. When set, only TERTIARY and above differences are
considered significant during comparison. The assignment of strengths
to language features is locale dependant. A common example is for
case differences ("a" vs "A") to be considered a TERTIARY difference.
Collator strength value. When set, all differences are
considered significant during comparison. The assignment of strengths
to language features is locale dependant. A common example is for control
characters ("\u0001" vs "\u0002") to be considered equal at the
PRIMARY, SECONDARY, and TERTIARY levels but different at the IDENTICAL
level. Additionally, differences between pre-composed accents such as
"\u00C0" (A-grave) and combining accents such as "A\u0300"
(A, combining-grave) will be considered significant at the IDENTICAL
level if decomposition is set to NO_DECOMPOSITION.
Decomposition mode value. With NO_DECOMPOSITION
set, accented characters will not be decomposed for collation. This
is the default setting and provides the fastest collation but
will only produce correct results for languages that do not use accents.
Decomposition mode value. With CANONICAL_DECOMPOSITION
set, characters that are canonical variants according to Unicode
standard will be decomposed for collation. This should be used to get
correct collation of accented characters.
CANONICAL_DECOMPOSITION corresponds to Normalization Form D as
described in
Unicode
Technical Report #15.
Decomposition mode value. With FULL_DECOMPOSITION
set, both Unicode canonical variants and Unicode compatibility variants
will be decomposed for collation. This causes not only accented
characters to be collated, but also characters that have special formats
to be collated with their norminal form. For example, the half-width and
full-width ASCII and Katakana characters are then collated together.
FULL_DECOMPOSITION is the most complete and therefore the slowest
decomposition mode.
FULL_DECOMPOSITION corresponds to Normalization Form KD as
described in
Unicode
Technical Report #15.
Gets the Collator for the current default locale.
The default locale is determined by java.util.Locale.getDefault.
Gets the Collator for the desired locale.
public static synchronized
if (providersInstance != null) { return providersInstance;
Compares the source string to the target string according to the
collation rules for this Collator. Returns an integer less than,
equal to or greater than zero depending on whether the source String is
less than, equal to or greater than the target string. See the Collator
class description for an example of use.
For a one time comparison, this method has the best performance. If a
given String will be involved in multiple comparisons, CollationKey.compareTo
has the best performance. See the Collator class description for an example
using CollationKeys.
- Parameters:
source the source string.target the target string.- Returns:
- Returns an integer value. Value is less than zero if source is less than
target, value is zero if source and target are equal, value is greater than zero
if source is greater than target.
- See also:
CollationKeygetCollationKey(java.lang.String)
Compares its two arguments for order. Returns a negative integer,
zero, or a positive integer as the first argument is less than, equal
to, or greater than the second.
This implementation merely returns
compare((String)o1, (String)o2) .
- Returns:
- a negative integer, zero, or a positive integer as the
first argument is less than, equal to, or greater than the
second.
- Throws:
java.lang.ClassCastException the arguments cannot be cast to Strings.- Since:
- 1.2
- See also:
java.util.Comparator
Transforms the String into a series of bits that can be compared bitwise
to other CollationKeys. CollationKeys provide better performance than
Collator.compare when Strings are involved in multiple comparisons.
See the Collator class description for an example using CollationKeys.
- Parameters:
source the string to be transformed into a collation key.- Returns:
- the CollationKey for the given String based on this Collator's collation
rules. If the source String is null, a null CollationKey is returned.
- See also:
CollationKeycompare(java.lang.String,java.lang.String)
Convenience method for comparing the equality of two strings based on
this Collator's collation rules.
- Parameters:
source the source string to be compared with.target the target string to be compared with.- Returns:
- true if the strings are equal according to the collation
rules. false, otherwise.
- See also:
compare(java.lang.String,java.lang.String)
Returns this Collator's strength property. The strength property determines
the minimum level of difference considered significant during comparison.
See the Collator class description for an example of use.
Sets this Collator's strength property. The strength property determines
the minimum level of difference considered significant during comparison.
See the Collator class description for an example of use.
public synchronized void setStrength(int newStrength) { Get the decomposition mode of this Collator. Decomposition mode
determines how Unicode composed characters are handled. Adjusting
decomposition mode allows the user to select between faster and more
complete collation behavior.
The three values for decomposition mode are:
- NO_DECOMPOSITION,
- CANONICAL_DECOMPOSITION
- FULL_DECOMPOSITION.
See the documentation for these three constants for a description
of their meaning.
Set the decomposition mode of this Collator. See getDecomposition
for a description of decomposition mode.
decmp = decompositionMode;
Returns an array of all locales for which the
getInstance methods of this class can return
localized instances.
The returned array represents the union of locales supported
by the Java runtime and by installed
CollatorProvider implementations.
It must contain at least a Locale instance equal to
Locale.US.
- Returns:
- An array of locales for which localized
Collator instances are available.
Compares the equality of two Collators.
- Parameters:
that the Collator to be compared with this.- Returns:
- true if this Collator is the same as that Collator;
false otherwise.
if (this == that) return true;
if (that == null) return false;
Generates the hash code for this Collator.
Default constructor. This constructor is
protected so subclasses can get access to it. Users typically create
a Collator sub-class by calling the factory method getInstance.
LESS is returned if source string is compared to be less than target
string in the compare() method.
final static int LESS = -1;
EQUAL is returned if source string is compared to be equal to target
string in the compare() method.
final static int EQUAL = 0;
GREATER is returned if source string is compared to be greater than
target string in the compare() method.
Obtains a Collator instance from a CollatorProvider
implementation.
assert params.length == 1;
