java.lang.Object | |
↳ | java.text.Collator |
Known Direct Subclasses |
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 String
s exactly once, the compare
method provides the best performance. When sorting a list of
String
s however, it is generally necessary to compare each
String
multiple times. In this case, CollationKey
s
provide better performance. The CollationKey
class converts
a String
to a series of bits that can be compared bitwise
against other CollationKey
s. A CollationKey
is
created by a Collator
object for a given String
.
Note: CollationKey
s from different
Collator
s can not be compared. See the class description
for CollationKey
for an example using CollationKey
s.
Constants | |||||||||||
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int | CANONICAL_DECOMPOSITION | Decomposition mode value. | |||||||||
int | FULL_DECOMPOSITION | Decomposition mode value. | |||||||||
int | IDENTICAL | Collator strength value. | |||||||||
int | NO_DECOMPOSITION | Decomposition mode value. | |||||||||
int | PRIMARY | Collator strength value. | |||||||||
int | SECONDARY | Collator strength value. | |||||||||
int | TERTIARY | Collator strength value. |
Protected Constructors | |||||||||||
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Default constructor.
|
Public Methods | |||||||||||
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Overrides Cloneable
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Compares the source string to the target string according to the
collation rules for this Collator.
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Compares its two arguments for order.
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Compares the equality of two Collators.
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Convenience method for comparing the equality of two strings based on
this Collator's collation rules.
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Returns an array of all locales for which the
getInstance methods of this class can return
localized instances. | |||||||||||
Transforms the String into a series of bits that can be compared bitwise
to other CollationKeys.
| |||||||||||
Get the decomposition mode of this Collator.
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Gets the Collator for the current default locale.
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Gets the Collator for the desired locale.
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Returns this Collator's strength property.
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Generates the hash code for this Collator.
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Set the decomposition mode of this Collator.
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Sets this Collator's strength property.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.lang.Object
| |||||||||||
From interface
java.util.Comparator
|
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.
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.
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.
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 "รค") 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.
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.
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.
source | the source string. |
---|---|
target | the target 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)
.
ClassCastException | the arguments cannot be cast to Strings. |
---|
Compares the equality of two Collators.
that | the Collator to be compared with this. |
---|
Convenience method for comparing the equality of two strings based on this Collator's collation rules.
source | the source string to be compared with. |
---|---|
target | the target string to be compared with. |
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
.
Collator
instances are available.
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.
source | the string to be transformed into a collation key. |
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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:
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.
desiredLocale | the desired locale. |
---|
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.
Generates the hash code for this Collator.
Set the decomposition mode of this Collator. See getDecomposition for a description of decomposition mode.
decompositionMode | the new decomposition mode. |
---|
IllegalArgumentException | If the given value is not a valid decomposition mode. |
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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.
newStrength | the new strength value. |
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IllegalArgumentException | If the new strength value is not one of PRIMARY, SECONDARY, TERTIARY or IDENTICAL. |
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