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CollationKey.java
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149 lines (139 loc) · 4.79 KB
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/*
* Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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/*
* (C) Copyright Taligent, Inc. 1996 - All Rights Reserved
* (C) Copyright IBM Corp. 1996 - All Rights Reserved
*
* The original version of this source code and documentation is copyrighted
* and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
* materials are provided under terms of a License Agreement between Taligent
* and Sun. This technology is protected by multiple US and International
* patents. This notice and attribution to Taligent may not be removed.
* Taligent is a registered trademark of Taligent, Inc.
*
*/
package java.text;
/**
* A <code>CollationKey</code> represents a <code>String</code> under the
* rules of a specific <code>Collator</code> object. Comparing two
* <code>CollationKey</code>s returns the relative order of the
* <code>String</code>s they represent. Using <code>CollationKey</code>s
* to compare <code>String</code>s is generally faster than using
* <code>Collator.compare</code>. Thus, when the <code>String</code>s
* must be compared multiple times, for example when sorting a list
* of <code>String</code>s. It's more efficient to use <code>CollationKey</code>s.
*
* <p>
* You can not create <code>CollationKey</code>s directly. Rather,
* generate them by calling <code>Collator.getCollationKey</code>.
* You can only compare <code>CollationKey</code>s generated from
* the same <code>Collator</code> object.
*
* <p>
* Generating a <code>CollationKey</code> for a <code>String</code>
* involves examining the entire <code>String</code>
* 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 <code>String</code>s 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 <code>String</code>.
* <code>Collator.compare</code> examines only as many characters as it needs which
* allows it to be faster when doing single comparisons.
* <p>
* The following example shows how <code>CollationKey</code>s might be used
* to sort a list of <code>String</code>s.
* <blockquote>
* <pre>{@code
* // 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());
* }</pre>
* </blockquote>
*
* @see Collator
* @see RuleBasedCollator
* @author Helena Shih
*/
public abstract class CollationKey implements Comparable<CollationKey> {
/**
* Compare this CollationKey to the target CollationKey. The collation rules of the
* Collator object which created these keys are applied. <strong>Note:</strong>
* CollationKeys created by different Collators can not be compared.
* @param target target CollationKey
* @return 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 java.text.Collator#compare
*/
abstract public int compareTo(CollationKey target);
/**
* Returns the String that this CollationKey represents.
*
* @return the source string of this CollationKey
*/
public String getSourceString() {
return source;
}
/**
* 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.
*
* @return a byte array representation of the CollationKey
*/
abstract public byte[] toByteArray();
/**
* CollationKey constructor.
*
* @param source the source string
* @exception NullPointerException if {@code source} is null
* @since 1.6
*/
protected CollationKey(String source) {
if (source==null){
throw new NullPointerException();
}
this.source = source;
}
final private String source;
}