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Collator.javaAPI DocJava SE 5 API19778Fri Aug 26 14:57:20 BST 2005java.text

Collator

public abstract class Collator extends Object implements Cloneable, Comparator
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 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 {@link CollationKey} for an example using CollationKeys.

see
RuleBasedCollator
see
CollationKey
see
CollationElementIterator
see
Locale
version
1.39, 05/05/04
author
Helena Shih, Laura Werner, Richard Gillam

Fields Summary
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.
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 "\u00E4") to be considered a SECONDARY difference.
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.
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 IDENTICAL level if decomposition is set to NO_DECOMPOSITION.
public static final 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.
public static final 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.

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 KD as described in Unicode Technical Report #15.

private int
strength
private int
decmp
private static sun.misc.SoftCache
cache
static final int
LESS
LESS is returned if source string is compared to be less than target string in the compare() method.
static final int
EQUAL
EQUAL is returned if source string is compared to be equal to target string in the compare() method.
static final int
GREATER
GREATER is returned if source string is compared to be greater than target string in the compare() method.
Constructors Summary
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
java.text.Collator#getInstance

        strength = TERTIARY;
        decmp = CANONICAL_DECOMPOSITION;
Methods Summary
public java.lang.Objectclone()
Overrides Cloneable

        try {
            return (Collator)super.clone();
        } catch (CloneNotSupportedException e) {
            throw new InternalError();
        }
public abstract intcompare(java.lang.String source, java.lang.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.

param
source the source string.
param
target the target string.
return
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
java.text.CollationKey
see
java.text.Collator#getCollationKey

public intcompare(java.lang.Object o1, java.lang.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) .
return
a negative integer, zero, or a positive integer as the
first argument is less than, equal to, or greater than the
second.
exception
ClassCastException the arguments cannot be cast to Strings.
see
java.util.Comparator
since
1.2
    return compare((String)o1, (String)o2);
    
public booleanequals(java.lang.Object that)
Compares the equality of two Collators.
param
that the Collator to be compared with this.
return
true if this Collator is the same as that Collator;
false otherwise.
        if (this == that) return true;
        if (that == null) return false;
        if (getClass() != that.getClass()) return false;
        Collator other = (Collator) that;
        return ((strength == other.strength) &&
                (decmp == other.decmp));
    
public booleanequals(java.lang.String source, java.lang.String target)
Convenience method for comparing the equality of two strings based on
this Collator's collation rules.
param
source the source string to be compared with.
param
target the target string to be compared with.
return
true if the strings are equal according to the collation
rules. false, otherwise.
see
java.text.Collator#compare
        return (compare(source, target) == Collator.EQUAL);
    
public static synchronized java.util.Locale[]getAvailableLocales()
Returns an array of all locales for which the
getInstance methods of this class can return
localized instances.
The array returned must contain at least a Locale
instance equal to {@link java.util.Locale#US Locale.US}.
return
An array of locales for which localized
Collator instances are available.
        return LocaleData.getAvailableLocales("CollationElements");
    
public abstract java.text.CollationKeygetCollationKey(java.lang.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.
param
source the string to be transformed into a collation key.
return
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
java.text.CollationKey
see
java.text.Collator#compare
public synchronized intgetDecomposition()
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.
return
the decomposition mode
see
java.text.Collator#setDecomposition
see
java.text.Collator#NO_DECOMPOSITION
see
java.text.Collator#CANONICAL_DECOMPOSITION
see
java.text.Collator#FULL_DECOMPOSITION
        return decmp;
    
public static synchronized java.text.CollatorgetInstance()
Gets the Collator for the current default locale.
The default locale is determined by java.util.Locale.getDefault.
return
the Collator for the default locale.(for example, en_US)
see
java.util.Locale#getDefault

                                   
         
        return getInstance(Locale.getDefault());
    
public static synchronized java.text.CollatorgetInstance(java.util.Locale desiredLocale)
Gets the Collator for the desired locale.
param
desiredLocale the desired locale.
return
the Collator for the desired locale.
see
java.util.Locale
see
java.util.ResourceBundle
        RuleBasedCollator result = null;
        result = (RuleBasedCollator) cache.get(desiredLocale);
        if (result != null) {
                 return (Collator)result.clone();  // make the world safe
        }

        // Load the resource of the desired locale from resource
        // manager.
        String colString = "";
        int decomp = CANONICAL_DECOMPOSITION;
        
        try {
            ResourceBundle resource = LocaleData.getLocaleElements(desiredLocale);

            colString = resource.getString("CollationElements");
            decomp = ((Integer)resource.getObject("CollationDecomp")).intValue();
        } catch (MissingResourceException e) {
            // Use default values
        }
        try
        {
            result = new RuleBasedCollator( CollationRules.DEFAULTRULES +
                                            colString,
                                            decomp );
        }
        catch(ParseException foo)
        {
            // predefined tables should contain correct grammar
            try {
                result = new RuleBasedCollator( CollationRules.DEFAULTRULES );
            } catch (ParseException bar) {
                // do nothing
            }
        }
        // Now that RuleBasedCollator adds expansions for pre-composed characters
        // into their decomposed equivalents, the default collators don't need
        // to have decomposition turned on.  Laura, 5/5/98, bug 4114077
        result.setDecomposition(NO_DECOMPOSITION);
        
        cache.put(desiredLocale,result);
        return (Collator)result.clone();
    
public synchronized intgetStrength()
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.
return
this Collator's current strength property.
see
java.text.Collator#setStrength
see
java.text.Collator#PRIMARY
see
java.text.Collator#SECONDARY
see
java.text.Collator#TERTIARY
see
java.text.Collator#IDENTICAL
        return strength;
    
public abstract inthashCode()
Generates the hash code for this Collator.
public synchronized voidsetDecomposition(int decompositionMode)
Set the decomposition mode of this Collator. See getDecomposition
for a description of decomposition mode.
param
decompositionMode the new decomposition mode.
see
java.text.Collator#getDecomposition
see
java.text.Collator#NO_DECOMPOSITION
see
java.text.Collator#CANONICAL_DECOMPOSITION
see
java.text.Collator#FULL_DECOMPOSITION
exception
IllegalArgumentException If the given value is not a valid decomposition
mode.
        if ((decompositionMode != NO_DECOMPOSITION) &&
            (decompositionMode != CANONICAL_DECOMPOSITION) &&
            (decompositionMode != FULL_DECOMPOSITION))
            throw new IllegalArgumentException("Wrong decomposition mode.");
        decmp = decompositionMode;
    
public synchronized voidsetStrength(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.
param
newStrength the new strength value.
see
java.text.Collator#getStrength
see
java.text.Collator#PRIMARY
see
java.text.Collator#SECONDARY
see
java.text.Collator#TERTIARY
see
java.text.Collator#IDENTICAL
exception
IllegalArgumentException If the new strength value is not one of
PRIMARY, SECONDARY, TERTIARY or IDENTICAL.
        if ((newStrength != PRIMARY) &&
            (newStrength != SECONDARY) &&
            (newStrength != TERTIARY) &&
            (newStrength != IDENTICAL))
            throw new IllegalArgumentException("Incorrect comparison level.");
        strength = newStrength;