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package org.apache.lucene.util;
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import java.util.Comparator;
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import java.util.StringTokenizer;
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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* Methods for manipulating strings.
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public abstract class StringHelper {
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* The StringInterner implementation used by Lucene.
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* This shouldn't be changed to an incompatible implementation after other Lucene APIs have been used.
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public static StringInterner interner = new SimpleStringInterner(1024,8);
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/** Return the same string object for all equal strings */
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public static String intern(String s) {
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return interner.intern(s);
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* Compares two byte[] arrays, element by element, and returns the
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* number of elements common to both arrays.
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* @param bytes1 The first byte[] to compare
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* @param bytes2 The second byte[] to compare
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* @return The number of common elements.
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public static final int bytesDifference(byte[] bytes1, int len1, byte[] bytes2, int len2) {
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int len = len1 < len2 ? len1 : len2;
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for (int i = 0; i < len; i++)
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if (bytes1[i] != bytes2[i])
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private StringHelper() {
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* @return a Comparator over versioned strings such as X.YY.Z
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public static Comparator<String> getVersionComparator() {
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return versionComparator;
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private static Comparator<String> versionComparator = new Comparator<String>() {
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public int compare(String a, String b) {
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StringTokenizer aTokens = new StringTokenizer(a, ".");
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StringTokenizer bTokens = new StringTokenizer(b, ".");
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while (aTokens.hasMoreTokens()) {
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int aToken = Integer.parseInt(aTokens.nextToken());
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if (bTokens.hasMoreTokens()) {
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int bToken = Integer.parseInt(bTokens.nextToken());
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if (aToken != bToken) {
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return aToken < bToken ? -1 : 1;
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// a has some extra trailing tokens. if these are all zeroes, thats ok.
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// b has some extra trailing tokens. if these are all zeroes, thats ok.
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while (bTokens.hasMoreTokens()) {
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if (Integer.parseInt(bTokens.nextToken()) != 0)