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Lucene example source code file (ScriptIterator.java)

This example Lucene source code file (ScriptIterator.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

scriptiterator, scriptiterator

The Lucene ScriptIterator.java source code

package org.apache.lucene.analysis.icu.segmentation;

/** 
 * Copyright (C) 1999-2010, International Business Machines
 * Corporation and others.  All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy 
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights 
 * to use, copy, modify, merge, publish, distribute, and/or sell copies of the 
 * Software, and to permit persons to whom the Software is furnished to do so, 
 * provided that the above copyright notice(s) and this permission notice appear 
 * in all copies of the Software and that both the above copyright notice(s) and
 * this permission notice appear in supporting documentation.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS. 
 * IN NO EVENT SHALL THE COPYRIGHT HOLDER OR HOLDERS INCLUDED IN THIS NOTICE BE 
 * LIABLE FOR ANY CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL DAMAGES, OR 
 * ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER 
 * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT 
 * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 * Except as contained in this notice, the name of a copyright holder shall not 
 * be used in advertising or otherwise to promote the sale, use or other 
 * dealings in this Software without prior written authorization of the 
 * copyright holder.
 */

import com.ibm.icu.lang.UCharacter;
import com.ibm.icu.lang.UScript;
import com.ibm.icu.text.UTF16;

/**
 * An iterator that locates ISO 15924 script boundaries in text. 
 * <p>
 * This is not the same as simply looking at the Unicode block, or even the 
 * Script property. Some characters are 'common' across multiple scripts, and
 * some 'inherit' the script value of text surrounding them.
 * <p>
 * This is similar to ICU (internal-only) UScriptRun, with the following
 * differences:
 * <ul>
 *  <li>Doesn't attempt to match paired punctuation. For tokenization purposes, this
 * is not necessary. Its also quite expensive. 
 *  <li>Non-spacing marks inherit the script of their base character, following 
 *  recommendations from UTR #24.
 * </ul>
 * @lucene.experimental
 */
final class ScriptIterator {
  private char text[];
  private int start;
  private int limit;
  private int index;

  private int scriptStart;
  private int scriptLimit;
  private int scriptCode;

  /**
   * Get the start of this script run
   * 
   * @return start position of script run
   */
  int getScriptStart() {
    return scriptStart;
  }

  /**
   * Get the index of the first character after the end of this script run
   * 
   * @return position of the first character after this script run
   */
  int getScriptLimit() {
    return scriptLimit;
  }

  /**
   * Get the UScript script code for this script run
   * 
   * @return code for the script of the current run
   */
  int getScriptCode() {
    return scriptCode;
  }

  /**
   * Iterates to the next script run, returning true if one exists.
   * 
   * @return true if there is another script run, false otherwise.
   */
  boolean next() {
    if (scriptLimit >= limit)
      return false;

    scriptCode = UScript.COMMON;
    scriptStart = scriptLimit;

    while (index < limit) {
      final int ch = UTF16.charAt(text, start, limit, index - start);
      final int sc = getScript(ch);

      /*
       * From UTR #24: Implementations that determine the boundaries between
       * characters of given scripts should never break between a non-spacing
       * mark and its base character. Thus for boundary determinations and
       * similar sorts of processing, a non-spacing mark — whatever its script
       * value — should inherit the script value of its base character.
       */
      if (isSameScript(scriptCode, sc)
          || UCharacter.getType(ch) == UCharacter.NON_SPACING_MARK) {
        index += UTF16.getCharCount(ch);

        /*
         * Inherited or Common becomes the script code of the surrounding text.
         */
        if (scriptCode <= UScript.INHERITED && sc > UScript.INHERITED) {
          scriptCode = sc;
        }

      } else {
        break;
      }
    }

    scriptLimit = index;
    return true;
  }

  /** Determine if two scripts are compatible. */
  private static boolean isSameScript(int scriptOne, int scriptTwo) {
    return scriptOne <= UScript.INHERITED || scriptTwo <= UScript.INHERITED
        || scriptOne == scriptTwo;
  }

  /**
   * Set a new region of text to be examined by this iterator
   * 
   * @param text text buffer to examine
   * @param start offset into buffer
   * @param length maximum length to examine
   */
  void setText(char text[], int start, int length) {
    this.text = text;
    this.start = start;
    this.index = start;
    this.limit = start + length;
    this.scriptStart = start;
    this.scriptLimit = start;
    this.scriptCode = UScript.INVALID_CODE;
  }

  /** linear fast-path for basic latin case */
  private static final int basicLatin[] = new int[128];

  static {
    for (int i = 0; i < basicLatin.length; i++)
      basicLatin[i] = UScript.getScript(i);
  }

  /** fast version of UScript.getScript(). Basic Latin is an array lookup */
  private static int getScript(int codepoint) {
    if (0 <= codepoint && codepoint < basicLatin.length)
      return basicLatin[codepoint];
    else
      return UScript.getScript(codepoint);
  }
}

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