Collator

public abstract class Collator extends Object
implements Comparator<Object> 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 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.

Constant Summary

int CANONICAL_DECOMPOSITION Constant used to specify the decomposition rule.
int FULL_DECOMPOSITION Constant used to specify the decomposition rule.
int IDENTICAL Constant used to specify the collation strength.
int NO_DECOMPOSITION Constant used to specify the decomposition rule.
int PRIMARY Constant used to specify the collation strength.
int SECONDARY Constant used to specify the collation strength.
int TERTIARY Constant used to specify the collation strength.

Public Constructor Summary

Public Method Summary

Object
clone()
int
compare(Object object1, Object object2)
Compares two objects to determine their relative order.
abstract int
compare(String string1, String string2)
Compares two strings to determine their relative order.
boolean
equals(String string1, String string2)
Compares two strings using the collation rules to determine if they are equal.
static Locale[]
getAvailableLocales()
Returns an array of locales for which custom Collator instances are available.
abstract CollationKey
getCollationKey(String string)
Returns a CollationKey for the specified string for this collator with the current decomposition rule and strength value.
abstract int
getDecomposition()
Returns the decomposition rule for this collator.
static Collator
getInstance()
Returns a Collator instance which is appropriate for the user's default Locale.
static Collator
getInstance(Locale locale)
Returns a Collator instance which is appropriate for locale.
abstract int
getStrength()
Returns the strength value for this collator.
abstract void
setDecomposition(int value)
Sets the decomposition rule for this collator.
abstract void
setStrength(int value)
Sets the strength value for this collator.

Inherited Method Summary

Constants

public static final int CANONICAL_DECOMPOSITION

Constant used to specify the decomposition rule.

Constant Value: 1

public static final int FULL_DECOMPOSITION

Constant used to specify the decomposition rule. This value for decomposition is not supported.

Constant Value: 2

public static final int IDENTICAL

Constant used to specify the collation strength.

Constant Value: 3

public static final int NO_DECOMPOSITION

Constant used to specify the decomposition rule.

Constant Value: 0

public static final int PRIMARY

Constant used to specify the collation strength.

Constant Value: 0

public static final int SECONDARY

Constant used to specify the collation strength.

Constant Value: 1

public static final int TERTIARY

Constant used to specify the collation strength.

Constant Value: 2

Public Constructors

public Collator ()

Public Methods

public Object clone ()

public int compare (Object object1, Object object2)

Compares two objects to determine their relative order. The objects must be strings.

Parameters
object1 the first string to compare.
object2 the second string to compare.
Returns
  • a negative value if object1 is less than object2, 0 if they are equal, and a positive value if object1 is greater than object2.
Throws
ClassCastException if object1 or object2 is not a String.

public abstract int compare (String string1, String string2)

Compares two strings to determine their relative order.

Parameters
string1 the first string to compare.
string2 the second string to compare.
Returns
  • a negative value if string1 is less than string2, 0 if they are equal and a positive value if string1 is greater than string2.

public boolean equals (String string1, String string2)

Compares two strings using the collation rules to determine if they are equal.

Parameters
string1 the first string to compare.
string2 the second string to compare.
Returns
  • true if string1 and string2 are equal using the collation rules, false otherwise.

public static Locale[] getAvailableLocales ()

Returns an array of locales for which custom Collator instances are available.

Note that Android does not support user-supplied locale service providers.

public abstract CollationKey getCollationKey (String string)

Returns a CollationKey for the specified string for this collator with the current decomposition rule and strength value.

Parameters
string the source string that is converted into a collation key.
Returns
  • the collation key for string.

public abstract int getDecomposition ()

Returns the decomposition rule for this collator.

Returns
  • the decomposition rule, either NO_DECOMPOSITION or CANONICAL_DECOMPOSITION. FULL_DECOMPOSITION is not supported.

public static Collator getInstance ()

Returns a Collator instance which is appropriate for the user's default Locale. See "Be wary of the default locale".

public static Collator getInstance (Locale locale)

Returns a Collator instance which is appropriate for locale.

Parameters
locale

public abstract int getStrength ()

Returns the strength value for this collator.

Returns
  • the strength value, either PRIMARY, SECONDARY, TERTIARY or IDENTICAL.

public abstract void setDecomposition (int value)

Sets the decomposition rule for this collator.

Parameters
value the decomposition rule, either NO_DECOMPOSITION or CANONICAL_DECOMPOSITION. FULL_DECOMPOSITION is not supported.
Throws
IllegalArgumentException if the provided decomposition rule is not valid. This includes FULL_DECOMPOSITION.

public abstract void setStrength (int value)

Sets the strength value for this collator.

Parameters
value the strength value, either PRIMARY, SECONDARY, TERTIARY, or IDENTICAL.
Throws
IllegalArgumentException if the provided strength value is not valid.