java.text
Class Collator

java.lang.Object
  |
  +--java.text.Collator

Direct Known Subclasses:

RuleBasedCollator

public abstract class Collator

extends Object

implements Comparator, Cloneable

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 JDK 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 "ê" 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 CollationKey for an example using CollationKeys.

See Also:

RuleBasedCollator, CollationKey, CollationElementIterator, Locale

Field Summary

static int	CANONICAL_DECOMPOSITION Decomposition mode value.
static int	FULL_DECOMPOSITION Decomposition mode value.
static int	IDENTICAL Collator strength value.
static int	NO_DECOMPOSITION Decomposition mode value.
static int	PRIMARY Collator strength value.
static int	SECONDARY Collator strength value.
static int	TERTIARY Collator strength value.

Constructor Summary

protected

Collator() Default constructor.

Method Summary

Object	clone() Overrides Cloneable
int	compare(Object o1, Object o2) Compares its two arguments for order.
abstract int	compare(String source, String target) Compares the source string to the target string according to the collation rules for this Collator.
boolean	equals(Object that) Compares the equality of two Collators.
boolean	equals(String source, String target) Convenience method for comparing the equality of two strings based on this Collator's collation rules.
static Locale[]	getAvailableLocales() Get the set of Locales for which Collators are installed.
abstract CollationKey	getCollationKey(String source) Transforms the String into a series of bits that can be compared bitwise to other CollationKeys.
int	getDecomposition() Get the decomposition mode of this Collator.
static Collator	getInstance() Gets the Collator for the current default locale.
static Collator	getInstance(Locale desiredLocale) Gets the Collator for the desired locale.
int	getStrength() Returns this Collator's strength property.
abstract int	hashCode() Generates the hash code for this Collator.
void	setDecomposition(int decompositionMode) Set the decomposition mode of this Collator.
void	setStrength(int newStrength) Sets this Collator's strength property.

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Field Detail

PRIMARY

public static final int PRIMARY

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.

See Also:

setStrength(int), getStrength()

SECONDARY

public static final int SECONDARY

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 "ä") to be considered a SECONDARY difference.

See Also:

setStrength(int), getStrength()

TERTIARY

public static final int TERTIARY

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.

See Also:

setStrength(int), getStrength()

IDENTICAL

public static final int IDENTICAL

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 tertiary level if decomposition is set to NO_DECOMPOSITION.

NO_DECOMPOSITION

public static final int NO_DECOMPOSITION

Decomposition mode value. With NO_DECOMPOSITION set, accented characters will not be decomposed for collation. This provides the fastest collation but will only produce correct results for languages that do not use accents.

See Also:

getDecomposition(), setDecomposition(int)

CANONICAL_DECOMPOSITION

public static final int CANONICAL_DECOMPOSITION

Decomposition mode value. With CANONICAL_DECOMPOSITION set, characters that are canonical variants according to Unicode 2.0 will be decomposed for collation. This is the default setting and should be used to get correct collation of accented characters.

CANONICAL_DECOMPOSITION corresponds to Normalization Form D as described in Unicode Technical Report #15.

See Also:

getDecomposition(), setDecomposition(int)

FULL_DECOMPOSITION

public static final int FULL_DECOMPOSITION

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 DC as described in Unicode Technical Report #15.

See Also:

getDecomposition(), setDecomposition(int)

Constructor Detail

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:

getInstance()

Method Detail

getInstance

public static Collator getInstance()

Gets the Collator for the current default locale. The default locale is determined by java.util.Locale.getDefault.

Returns:

the Collator for the default locale.(for example, en_US)

See Also:

Locale.getDefault()

getInstance

public static Collator getInstance(Locale desiredLocale)

Gets the Collator for the desired locale.

Parameters:

desiredLocale - the desired locale.

Returns:

the Collator for the desired locale.

See Also:

Locale, ResourceBundle

compare

public abstract int compare(String source,
                            String target)

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:

CollationKey, getCollationKey(java.lang.String)

compare

public int compare(Object o1,
                   Object o2)

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:

compare in interface Comparator

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:

JDK1.2

See Also:

Comparator

getCollationKey

public abstract CollationKey getCollationKey(String source)

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:

CollationKey, compare(java.lang.String, java.lang.String)

equals

public boolean equals(String source,
                      String target)

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)

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:

setStrength(int), PRIMARY, SECONDARY, TERTIARY, IDENTICAL

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:

the - new strength value.

Throws:

IllegalArgumentException - If the new strength value is not one of PRIMARY, SECONDARY, TERTIARY or IDENTICAL.

See Also:

getStrength(), PRIMARY, SECONDARY, TERTIARY, IDENTICAL

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.

See the documentation for these three constants for a description of their meaning.

Returns:

the decomposition mode

See Also:

setDecomposition(int), NO_DECOMPOSITION, CANONICAL_DECOMPOSITION, FULL_DECOMPOSITION

setDecomposition

public void setDecomposition(int decompositionMode)

Set the decomposition mode of this Collator. See getDecomposition for a description of decomposition mode.

Parameters:

the - new decomposition mode

Throws:

IllegalArgumentException - If the given value is not a valid decomposition mode.

See Also:

getDecomposition(), NO_DECOMPOSITION, CANONICAL_DECOMPOSITION, FULL_DECOMPOSITION

getAvailableLocales

public static Locale[] getAvailableLocales()

Get the set of Locales for which Collators are installed.

Returns:

the list of available locales which collators are installed.

clone

public Object clone()

Overrides Cloneable

Overrides:

clone in class Object

equals

public boolean equals(Object that)

Compares the equality of two Collators.

Specified by:

equals in interface Comparator

Parameters:

that - the Collator to be compared with this.

Returns:

true if this Collator is the same as that Collator; false otherwise.

Overrides:

equals in class Object

hashCode

public abstract int hashCode()

Generates the hash code for this Collator.

Overrides:

hashCode in class Object