Java Doc for Collator.java in  » 6.0-JDK-Modules » j2me » java » text » Java Source Code / Java DocumentationJava Source Code and Java Documentation

Collator is an abstract base class. Subclasses implement specific collation strategies. One subclass, RuleBasedCollator, is currently provided with the Java 2 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 "\u00EA" 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
See Also:   CollationKey
See Also:   CollationElementIterator
See Also:   Locale
version:
   1.34, 01/27/03
author:
   Helena Shih, Laura Werner, Richard Gillam

CANONICAL_DECOMPOSITION corresponds to Normalization Form D as described in Unicode Technical Report #15.
See Also:   java.text.Collator.getDecomposition
See Also:   java.text.Collator.setDecomposition

FULL_DECOMPOSITION corresponds to Normalization Form KD as described in Unicode Technical Report #15.
See Also:   java.text.Collator.getDecomposition
See Also:   java.text.Collator.setDecomposition

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.
Parameters:
  target - the target string. Returns an integer value. Value is less than zero if source is less thantarget, value is zero if source and target are equal, value is greater than zeroif source is greater than target.
See Also:   java.text.CollationKey
See Also:   java.text.Collator.getCollationKey

This implementation merely returns compare((String)o1, (String)o2) . a negative integer, zero, or a positive integer as thefirst argument is less than, equal to, or greater than thesecond.
exception:
  ClassCastException - the arguments cannot be cast to Strings.
See Also:   java.util.Comparator
since:
   1.2

The three values for decomposition mode are:

• NO_DECOMPOSITION,
• CANONICAL_DECOMPOSITION
• FULL_DECOMPOSITION.