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Collator

public abstract class Collator
extends Object implements Comparator<Object>, Cloneable

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 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:

Summary

Constants

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

Collator()

Default constructor.

Public methods

Object clone()

Returns a new collator with the same decomposition mode and strength value as this collator.

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(String source, String target)

Convenience method for comparing the equality of two strings based on this Collator's collation rules.

boolean equals(Object that)

Compares the equality of two Collators.

static Locale[] getAvailableLocales()

Returns an array of all locales for which the getInstance methods of this class can return localized instances.

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.

Inherited methods

From class java.lang.Object
From interface java.util.Comparator

Constants

CANONICAL_DECOMPOSITION

Added in API level 1
int CANONICAL_DECOMPOSITION

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.

See also:

Constant Value: 1 (0x00000001)

FULL_DECOMPOSITION

Added in API level 1
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 KD as described in Unicode Technical Report #15.

See also:

Constant Value: 2 (0x00000002)

IDENTICAL

Added in API level 1
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 IDENTICAL level if decomposition is set to NO_DECOMPOSITION.

Constant Value: 3 (0x00000003)

NO_DECOMPOSITION

Added in API level 1
int 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.

See also:

Constant Value: 0 (0x00000000)

PRIMARY

Added in API level 1
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:

Constant Value: 0 (0x00000000)

SECONDARY

Added in API level 1
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:

Constant Value: 1 (0x00000001)

TERTIARY

Added in API level 1
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:

Constant Value: 2 (0x00000002)

Protected constructors

Collator

Added in API level 1
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:

Public methods

clone

Added in API level 1
Object clone ()

Returns a new collator with the same decomposition mode and strength value as this collator.

Returns
Object a shallow copy of this collator.

See also:

compare

Added in API level 1
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) .

Parameters
o1 Object
o2 Object
Returns
int 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.

See also:

compare

Added in API level 1
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 String: the source string.
target String: the target string.
Returns
int 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:

equals

Added in API level 1
boolean equals (String source, 
                String target)

Convenience method for comparing the equality of two strings based on this Collator's collation rules.

Parameters
source String: the source string to be compared with.
target String: the target string to be compared with.
Returns
boolean true if the strings are equal according to the collation rules. false, otherwise.

See also:

equals

Added in API level 1
boolean equals (Object that)

Compares the equality of two Collators.

Parameters
that Object: the Collator to be compared with this.
Returns
boolean true if this Collator is the same as that Collator; false otherwise.

getAvailableLocales

Added in API level 1
Locale[] getAvailableLocales ()

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
Locale[] An array of locales for which localized Collator instances are available.

getCollationKey

Added in API level 1
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 String: the string to be transformed into a collation key.
Returns
CollationKey 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:

getDecomposition

Added in API level 1
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
int the decomposition mode

See also:

getInstance

Added in API level 1
Collator getInstance ()

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

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

See also:

getInstance

Added in API level 1
Collator getInstance (Locale desiredLocale)

Gets the Collator for the desired locale.

Parameters
desiredLocale Locale: the desired locale.
Returns
Collator the Collator for the desired locale.

See also:

getStrength

Added in API level 1
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
int this Collator's current strength property.

See also:

hashCode

Added in API level 1
int hashCode ()

Generates the hash code for this Collator.

Returns
int a hash code value for this object.

setDecomposition

Added in API level 1
void setDecomposition (int decompositionMode)

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

Parameters
decompositionMode int: the new decomposition mode.
Throws
IllegalArgumentException If the given value is not a valid decomposition mode.

See also:

setStrength

Added in API level 1
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 int: 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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