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26 /*
27  * (C) Copyright Taligent, Inc. 1996 - All Rights Reserved
28  * (C) Copyright IBM Corp. 1996 - All Rights Reserved
29  *
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36  *
37  */
38 
39 package java.text;
40 
41 /**
42  * A <code>CollationKey</code> represents a <code>String</code> under the
43  * rules of a specific <code>Collator</code> object. Comparing two
44  * <code>CollationKey</code>s returns the relative order of the
45  * <code>String</code>s they represent. Using <code>CollationKey</code>s
46  * to compare <code>String</code>s is generally faster than using
47  * <code>Collator.compare</code>. Thus, when the <code>String</code>s
48  * must be compared multiple times, for example when sorting a list
49  * of <code>String</code>s. It's more efficient to use <code>CollationKey</code>s.
50  *
51  * <p>
52  * You can not create <code>CollationKey</code>s directly. Rather,
53  * generate them by calling <code>Collator.getCollationKey</code>.
54  * You can only compare <code>CollationKey</code>s generated from
55  * the same <code>Collator</code> object.
56  *
57  * <p>
58  * Generating a <code>CollationKey</code> for a <code>String</code>
59  * involves examining the entire <code>String</code>
60  * and converting it to series of bits that can be compared bitwise. This
61  * allows fast comparisons once the keys are generated. The cost of generating
62  * keys is recouped in faster comparisons when <code>String</code>s need
63  * to be compared many times. On the other hand, the result of a comparison
64  * is often determined by the first couple of characters of each <code>String</code>.
65  * <code>Collator.compare</code> examines only as many characters as it needs which
66  * allows it to be faster when doing single comparisons.
67  * <p>
68  * The following example shows how <code>CollationKey</code>s might be used
69  * to sort a list of <code>String</code>s.
70  * <blockquote>
71  * <pre>
72  * // Create an array of CollationKeys for the Strings to be sorted.
73  * Collator myCollator = Collator.getInstance();
74  * CollationKey[] keys = new CollationKey[3];
75  * keys[0] = myCollator.getCollationKey("Tom");
76  * keys[1] = myCollator.getCollationKey("Dick");
77  * keys[2] = myCollator.getCollationKey("Harry");
78  * sort( keys );
79  * <br>
80  * //...
81  * <br>
82  * // Inside body of sort routine, compare keys this way
83  * if( keys[i].compareTo( keys[j] ) > 0 )
84  *    // swap keys[i] and keys[j]
85  * <br>
86  * //...
87  * <br>
88  * // Finally, when we've returned from sort.
89  * System.out.println( keys[0].getSourceString() );
90  * System.out.println( keys[1].getSourceString() );
91  * System.out.println( keys[2].getSourceString() );
92  * </pre>
93  * </blockquote>
94  *
95  * @see          Collator
96  * @see          RuleBasedCollator
97  * @author       Helena Shih
98  */
99 
100 public abstract class CollationKey implements Comparable<CollationKey> {
101     /**
102      * Compare this CollationKey to the target CollationKey. The collation rules of the
103      * Collator object which created these keys are applied. <strong>Note:</strong>
104      * CollationKeys created by different Collators can not be compared.
105      * @param target target CollationKey
106      * @return Returns an integer value. Value is less than zero if this is less
107      * than target, value is zero if this and target are equal and value is greater than
108      * zero if this is greater than target.
109      * @see java.text.Collator#compare
110      */
compareTo(CollationKey target)111     abstract public int compareTo(CollationKey target);
112 
113     /**
114      * Returns the String that this CollationKey represents.
115      */
getSourceString()116     public String getSourceString() {
117         return source;
118     }
119 
120 
121     /**
122      * Converts the CollationKey to a sequence of bits. If two CollationKeys
123      * could be legitimately compared, then one could compare the byte arrays
124      * for each of those keys to obtain the same result.  Byte arrays are
125      * organized most significant byte first.
126      */
toByteArray()127     abstract public byte[] toByteArray();
128 
129 
130   /**
131    * CollationKey constructor.
132    *
133    * @param source - the source string.
134    * @exception NullPointerException if <code>source</code> is null.
135    * @since 1.6
136    */
CollationKey(String source)137     protected CollationKey(String source) {
138         if (source==null){
139             throw new NullPointerException();
140         }
141         this.source = source;
142     }
143 
144     final private String source;
145 }
146