1 /*
2 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
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24 */
25
26 /*
27 * (C) Copyright Taligent, Inc. 1996 - All Rights Reserved
28 * (C) Copyright IBM Corp. 1996 - All Rights Reserved
29 *
30 * The original version of this source code and documentation is copyrighted
31 * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
32 * materials are provided under terms of a License Agreement between Taligent
33 * and Sun. This technology is protected by multiple US and International
34 * patents. This notice and attribution to Taligent may not be removed.
35 * Taligent is a registered trademark of Taligent, Inc.
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>{@code
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 *
80 * //...
81 *
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 *
86 * //...
87 *
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 */
111 public abstract int compareTo(CollationKey target);
112
113 /**
114 * Returns the String that this CollationKey represents.
115 *
116 * @return the source string of this CollationKey
117 */
118 public String getSourceString() {
119 return source;
120 }
121
122
123 /**
124 * Converts the CollationKey to a sequence of bits. If two CollationKeys
125 * could be legitimately compared, then one could compare the byte arrays
126 * for each of those keys to obtain the same result. Byte arrays are
127 * organized most significant byte first.
128 *
129 * @return a byte array representation of the CollationKey
130 */
131 public abstract byte[] toByteArray();
132
133
134 /**
135 * CollationKey constructor.
136 *
137 * @param source the source string
138 * @exception NullPointerException if {@code source} is null
139 * @since 1.6
140 */
141 protected CollationKey(String source) {
142 if (source==null){
143 throw new NullPointerException();
144 }
145 this.source = source;
146 }
147
148 private final String source;
149 }