java.text
Class CollationKey

java.lang.Object
  java.text.CollationKey

All Implemented Interfaces:

Comparable

public final class CollationKey

extends Object

implements Comparable

A CollationKey represents a String under the rules of a specific Collator object. Comparing two CollationKeys returns the relative order of the Strings they represent. Using CollationKeys to compare Strings is generally faster than using Collator.compare. Thus, when the Strings must be compared multiple times, for example when sorting a list of Strings. It's more efficient to use CollationKeys.

You can not create CollationKeys directly. Rather, generate them by calling Collator.getCollationKey. You can only compare CollationKeys generated from the same Collator object.

Generating a CollationKey for a String involves examining the entire String and converting it to series of bits that can be compared bitwise. This allows fast comparisons once the keys are generated. The cost of generating keys is recouped in faster comparisons when Strings need to be compared many times. On the other hand, the result of a comparison is often determined by the first couple of characters of each String. Collator.compare examines only as many characters as it needs which allows it to be faster when doing single comparisons.

The following example shows how CollationKeys might be used to sort a list of Strings.

 // Create an array of CollationKeys for the Strings to be sorted.
 Collator myCollator = Collator.getInstance();
 CollationKey[] keys = new CollationKey[3];
 keys[0] = myCollator.getCollationKey("Tom");
 keys[1] = myCollator.getCollationKey("Dick");
 keys[2] = myCollator.getCollationKey("Harry");
 sort( keys );
 

 //...
 

 // Inside body of sort routine, compare keys this way
 if( keys[i].compareTo( keys[j] ) > 0 )
    // swap keys[i] and keys[j]
 

 //...
 

 // Finally, when we've returned from sort.
 System.out.println( keys[0].getSourceString() );
 System.out.println( keys[1].getSourceString() );
 System.out.println( keys[2].getSourceString() );
 

Author:

Helena Shih

See Also:

Collator, RuleBasedCollator

Field Summary

private String	key
private String	source

Constructor Summary

(package private)

CollationKey(String source, String key) A CollationKey can only be generated by Collator objects.

Method Summary

int	compareTo(CollationKey target) Compare this CollationKey to the target CollationKey.
int	compareTo(Object o) Compares this CollationKey with the specified Object for order.
boolean	equals(Object target) Compare this CollationKey and the target CollationKey for equality.
String	getSourceString() Returns the String that this CollationKey represents.
int	hashCode() Creates a hash code for this CollationKey.
byte[]	toByteArray() Converts the CollationKey to a sequence of bits.

Methods inherited from class java.lang.Object

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

Field Detail

source

private String source

key

private String key

Constructor Detail

CollationKey

CollationKey(String source,
             String key)

A CollationKey can only be generated by Collator objects.

Method Detail

compareTo

public int compareTo(CollationKey target)

Compare this CollationKey to the target CollationKey. The collation rules of the Collator object which created these keys are applied. Note: CollationKeys created by different Collators can not be compared.

Parameters:

target - target CollationKey

Returns:

Returns an integer value. Value is less than zero if this is less than target, value is zero if this and target are equal and value is greater than zero if this is greater than target.

See Also:

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

compareTo

public int compareTo(Object o)

Compares this CollationKey with the specified Object for order. Returns a negative integer, zero, or a positive integer as this CollationKey is less than, equal to, or greater than the given Object.

Specified by:

compareTo in interface Comparable

Parameters:

o - the Object to be compared.

Returns:

a negative integer, zero, or a positive integer as this Collation Key is less than, equal to, or greater than the given Object.

Throws:

ClassCastException - the specified Object is not a CollationKey.

Since:

1.2

See Also:

Comparable

equals

public boolean equals(Object target)

Compare this CollationKey and the target CollationKey for equality. The collation rules of the Collator object which created these keys are applied. Note: CollationKeys created by different Collators can not be compared.

Overrides:

equals in class Object

Parameters:

target - the CollationKey to compare to.

Returns:

Returns true if two objects are equal, false otherwise.

See Also:

Object.hashCode(), Hashtable

hashCode

public int hashCode()

Creates a hash code for this CollationKey. The hash value is calculated on the key itself, not the String from which the key was created. Thus if x and y are CollationKeys, then x.hashCode(x) == y.hashCode() if x.equals(y) is true. This allows language-sensitive comparison in a hash table. See the CollatinKey class description for an example.

Overrides:

hashCode in class Object

Returns:

the hash value based on the string's collation order.

See Also:

Object.equals(java.lang.Object), Hashtable

getSourceString

public String getSourceString()

Returns the String that this CollationKey represents.

toByteArray

public byte[] toByteArray()

Converts the CollationKey to a sequence of bits. If two CollationKeys could be legitimately compared, then one could compare the byte arrays for each of those keys to obtain the same result. Byte arrays are organized most significant byte first.