content: 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,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * 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<String>() {
      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;
      }
    };
  }
  