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Lucene example source code file (StringHelper.java)

This example Lucene source code file (StringHelper.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

comparator, comparator, simplestringinterner, string, string, stringhelper, stringhelper, stringinterner, stringtokenizer, stringtokenizer, util

The Lucene StringHelper.java source code

package org.apache.lucene.util;

import java.util.Comparator;
import java.util.StringTokenizer;

 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *     http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.

 * Methods for manipulating strings.
 * @lucene.internal
public abstract class StringHelper {
   * Expert:
   * The StringInterner implementation used by Lucene.
   * This shouldn't be changed to an incompatible implementation after other Lucene APIs have been used.
  public static StringInterner interner = new SimpleStringInterner(1024,8);

  /** Return the same string object for all equal strings */
  public static String intern(String s) {
    return interner.intern(s);

   * Compares two byte[] arrays, element by element, and returns the
   * number of elements common to both arrays.
   * @param bytes1 The first byte[] to compare
   * @param bytes2 The second byte[] to compare
   * @return The number of common elements.
  public static final int bytesDifference(byte[] bytes1, int len1, byte[] bytes2, int len2) {
    int len = len1 < len2 ? len1 : len2;
    for (int i = 0; i < len; i++)
      if (bytes1[i] != bytes2[i])
        return i;
    return len;
  private StringHelper() {
   * @return a Comparator over versioned strings such as X.YY.Z
   * @lucene.internal
  public static Comparator<String> getVersionComparator() {
    return versionComparator;
  private static Comparator<String> versionComparator = new Comparator() {
    public int compare(String a, String b) {
      StringTokenizer aTokens = new StringTokenizer(a, ".");
      StringTokenizer bTokens = new StringTokenizer(b, ".");
      while (aTokens.hasMoreTokens()) {
        int aToken = Integer.parseInt(aTokens.nextToken());
        if (bTokens.hasMoreTokens()) {
          int bToken = Integer.parseInt(bTokens.nextToken());
          if (aToken != bToken) {
            return aToken < bToken ? -1 : 1;
        } else {
          // a has some extra trailing tokens. if these are all zeroes, thats ok.
          if (aToken != 0) {
            return 1; 
      // b has some extra trailing tokens. if these are all zeroes, thats ok.
      while (bTokens.hasMoreTokens()) {
        if (Integer.parseInt(bTokens.nextToken()) != 0)
          return -1;
      return 0;

Other Lucene examples (source code examples)

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