- All Implemented Interfaces:
Cloneable,Comparator<Object>
- Direct Known Subclasses:
RuleBasedCollator
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 dependent. 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.
- API Note:
CollationKeys from differentCollators can not be compared. See the class description forCollationKeyfor an example usingCollationKeys.- Since:
- 1.1
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescriptionstatic final intDecomposition mode value.static final intDecomposition mode value.static final intCollator strength value.static final intDecomposition mode value.static final intCollator strength value.static final intCollator strength value.static final intCollator strength value. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionclone()Overrides CloneableintCompares its two arguments for order.abstract intCompares the source string to the target string according to the collation rules for this Collator.booleanCompares the equality of two Collators.booleanConvenience method for comparing the equality of two strings based on this Collator's collation rules.static Locale[]Returns an array of all locales for which thegetInstancemethods of this class can return localized instances.abstract CollationKeygetCollationKey(String source) Transforms the String into a series of bits that can be compared bitwise to other CollationKeys.intGet the decomposition mode of this Collator.static CollatorGets the Collator for the current default locale.static CollatorgetInstance(Locale desiredLocale) Gets the Collator for the desired locale.intReturns this Collator's strength property.abstract inthashCode()Generates the hash code for this Collator.voidsetDecomposition(int decompositionMode) Set the decomposition mode of this Collator.voidsetStrength(int newStrength) Sets this Collator's strength property.Methods declared in class java.lang.Object
finalize, getClass, notify, notifyAll, toString, wait, wait, waitMethods declared in interface java.util.Comparator
reversed, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong
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Field Details
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PRIMARY
public static final int PRIMARYCollator strength value. When set, only PRIMARY differences are considered significant during comparison. The assignment of strengths to language features is locale dependent. A common example is for different base letters ("a" vs "b") to be considered a PRIMARY difference.- See Also:
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SECONDARY
public static final int SECONDARYCollator strength value. When set, only SECONDARY and above differences are considered significant during comparison. The assignment of strengths to language features is locale dependent. A common example is for different accented forms of the same base letter ("a" vs "รค") to be considered a SECONDARY difference.- See Also:
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TERTIARY
public static final int TERTIARYCollator strength value. When set, only TERTIARY and above differences are considered significant during comparison. The assignment of strengths to language features is locale dependent. A common example is for case differences ("a" vs "A") to be considered a TERTIARY difference.- See Also:
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IDENTICAL
public static final int IDENTICALCollator strength value. When set, all differences are considered significant during comparison. The assignment of strengths to language features is locale dependent. 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.- See Also:
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NO_DECOMPOSITION
public static final int NO_DECOMPOSITIONDecomposition mode value. With NO_DECOMPOSITION set, accented characters will not be decomposed for collation. This setting provides the fastest collation but will only produce correct results for languages that do not use accents.- See Also:
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CANONICAL_DECOMPOSITION
public static final int CANONICAL_DECOMPOSITIONDecomposition 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 Standard Annex #15: Unicode Normalization Forms.
- External Specifications
- See Also:
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FULL_DECOMPOSITION
public static final int FULL_DECOMPOSITIONDecomposition 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 Standard Annex #15: Unicode Normalization Forms.
- External Specifications
- See Also:
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Constructor Details
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Collator
protected 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.- See Also:
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Method Details
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getInstance
Gets the Collator for the current default locale. The default locale is determined byLocale.getDefault().- Returns:
- the Collator for the default locale.(for example, en_US)
- See Also:
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getInstance
Gets the Collator for the desired locale. If the desired locale has the "ks" and/or the "kk" Unicode collation settings, this method will call setStrength(int) and/or setDecomposition(int) on the created instance, if the specified Unicode collation settings are recognized based on the following mappings:
Asterisk (*) denotes the default value. If the specified setting value is not recognized, the strength and/or decomposition is not overridden, as if there were no BCP 47 collation options in the desired locale.BCP 47 values for strength (ks) Collator constants for strength level1 PRIMARY level2 SECONDARY level3 TERTIARY* identic IDENTICAL BCP 47 values for normalization (kk) Collator constants for decomposition true CANONICAL_DECOMPOSITION false NO_DECOMPOSITION* - API Note:
- Implementations of
Collatorclass may produce different instances based on the "co" Unicode collation identifier in thedesiredLocale. For example:may return aCollator.getInstance(Locale.forLanguageTag("sv-u-co-trad"));Collatorinstance with the Swedish traditional sorting, which gives 'v' and 'w' the same sorting order, while theCollatorinstance for the Swedish locale without "co" identifier distinguishes 'v' and 'w'. - Parameters:
desiredLocale- the desired locale.- Returns:
- the Collator for the desired locale.
- External Specifications
- See Also:
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compare
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:
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compare
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).- Specified by:
comparein interfaceComparator<Object>- Parameters:
o1- the first object to be compared.o2- the second object to be compared.- Returns:
- a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.
- Throws:
ClassCastException- the arguments cannot be cast to Strings.- Since:
- 1.2
- See Also:
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getCollationKey
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:
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equals
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:
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getStrength
public int getStrength()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.- Returns:
- this Collator's current strength property.
- See Also:
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setStrength
public void setStrength(int newStrength) 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.- Parameters:
newStrength- the new strength value.- Throws:
IllegalArgumentException- If the new strength value is not one of PRIMARY, SECONDARY, TERTIARY or IDENTICAL.- See Also:
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getDecomposition
public int getDecomposition()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.
- Returns:
- the decomposition mode
- See Also:
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setDecomposition
public void setDecomposition(int decompositionMode) Set the decomposition mode of this Collator. See getDecomposition for a description of decomposition mode.- Parameters:
decompositionMode- the new decomposition mode.- Throws:
IllegalArgumentException- If the given value is not a valid decomposition mode.- See Also:
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getAvailableLocales
Returns an array of all locales for which thegetInstancemethods of this class can return localized instances. The returned array represents the union of locales supported by the Java runtime and by installedCollatorProviderimplementations. At a minimum, the returned array must contain aLocaleinstance equal toLocale.ROOTand aLocaleinstance equal toLocale.US.- Returns:
- An array of locales for which localized
Collatorinstances are available.
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clone
Overrides Cloneable -
equals
Compares the equality of two Collators.- Specified by:
equalsin interfaceComparator<Object>- Overrides:
equalsin classObject- Parameters:
that- the Collator to be compared with this.- Returns:
- true if this Collator is the same as that Collator; false otherwise.
- See Also:
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hashCode
public abstract int hashCode()Generates the hash code for this Collator.
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