151 lines
5.7 KiB
Java
151 lines
5.7 KiB
Java
/*
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* Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* (C) Copyright Taligent, Inc. 1996 - All Rights Reserved
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* (C) Copyright IBM Corp. 1996 - All Rights Reserved
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*
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* The original version of this source code and documentation is copyrighted
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* and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
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* materials are provided under terms of a License Agreement between Taligent
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* and Sun. This technology is protected by multiple US and International
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* patents. This notice and attribution to Taligent may not be removed.
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* Taligent is a registered trademark of Taligent, Inc.
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*
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*/
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package java.text;
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/**
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* A {@code CollationKey} represents a {@code String} under the
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* rules of a specific {@code Collator} object. Comparing two
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* {@code CollationKey}s returns the relative order of the
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* {@code String}s they represent. Using {@code CollationKey}s
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* to compare {@code String}s is generally faster than using
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* {@code Collator.compare}. Thus, when the {@code String}s
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* must be compared multiple times, for example when sorting a list
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* of {@code String}s. It's more efficient to use {@code CollationKey}s.
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*
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* <p>
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* You can not create {@code CollationKey}s directly. Rather,
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* generate them by calling {@code Collator.getCollationKey}.
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* You can only compare {@code CollationKey}s generated from
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* the same {@code Collator} object.
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*
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* <p>
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* Generating a {@code CollationKey} for a {@code String}
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* involves examining the entire {@code String}
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* and converting it to series of bits that can be compared bitwise. This
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* allows fast comparisons once the keys are generated. The cost of generating
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* keys is recouped in faster comparisons when {@code String}s need
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* to be compared many times. On the other hand, the result of a comparison
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* is often determined by the first couple of characters of each {@code String}.
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* {@code Collator.compare} examines only as many characters as it needs which
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* allows it to be faster when doing single comparisons.
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* <p>
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* The following example shows how {@code CollationKey}s might be used
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* to sort a list of {@code String}s.
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* <blockquote>
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* <pre>{@code
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* // Create an array of CollationKeys for the Strings to be sorted.
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* Collator myCollator = Collator.getInstance();
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* CollationKey[] keys = new CollationKey[3];
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* keys[0] = myCollator.getCollationKey("Tom");
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* keys[1] = myCollator.getCollationKey("Dick");
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* keys[2] = myCollator.getCollationKey("Harry");
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* sort(keys);
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*
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* //...
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*
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* // Inside body of sort routine, compare keys this way
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* if (keys[i].compareTo(keys[j]) > 0)
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* // swap keys[i] and keys[j]
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*
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* //...
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*
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* // Finally, when we've returned from sort.
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* System.out.println(keys[0].getSourceString());
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* System.out.println(keys[1].getSourceString());
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* System.out.println(keys[2].getSourceString());
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* }</pre>
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* </blockquote>
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*
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* @see Collator
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* @see RuleBasedCollator
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* @author Helena Shih
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* @since 1.1
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*/
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public abstract class CollationKey implements Comparable<CollationKey> {
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/**
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* Compare this CollationKey to the target CollationKey. The collation rules of the
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* Collator object which created these keys are applied. <strong>Note:</strong>
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* CollationKeys created by different Collators can not be compared.
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* @param target target CollationKey
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* @return Returns an integer value. Value is less than zero if this is less
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* than target, value is zero if this and target are equal and value is greater than
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* zero if this is greater than target.
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* @see java.text.Collator#compare
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*/
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public abstract int compareTo(CollationKey target);
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/**
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* Returns the String that this CollationKey represents.
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*
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* @return the source string of this CollationKey
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*/
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public String getSourceString() {
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return source;
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}
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/**
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* Converts the CollationKey to a sequence of bits. If two CollationKeys
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* could be legitimately compared, then one could compare the byte arrays
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* for each of those keys to obtain the same result. Byte arrays are
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* organized most significant byte first.
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*
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* @return a byte array representation of the CollationKey
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*/
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public abstract byte[] toByteArray();
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/**
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* CollationKey constructor.
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*
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* @param source the source string
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* @throws NullPointerException if {@code source} is null
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* @since 1.6
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*/
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protected CollationKey(String source) {
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if (source==null){
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throw new NullPointerException();
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}
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this.source = source;
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}
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private final String source;
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}
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