lucene/analysis/common/src/java/org/apache/lucene/analysis/core/LetterTokenizer.java

/*
 * 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.
 */
package org.apache.lucene.analysis.core;

import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.util.CharTokenizer;
import org.apache.lucene.util.AttributeFactory;

/**
 * A LetterTokenizer is a tokenizer that divides text at non-letters. That's to say, it defines
 * tokens as maximal strings of adjacent letters, as defined by java.lang.Character.isLetter()
 * predicate.
 *
 * <p>Note: this does a decent job for most European languages, but does a terrible job for some
 * Asian languages, where words are not separated by spaces.
 */
public class LetterTokenizer extends CharTokenizer {

  /** Construct a new LetterTokenizer. */
  public LetterTokenizer() {}

  /**
   * Construct a new LetterTokenizer using a given {@link org.apache.lucene.util.AttributeFactory}.
   *
   * @param factory the attribute factory to use for this {@link Tokenizer}
   */
  public LetterTokenizer(AttributeFactory factory) {
    super(factory);
  }

  /**
   * Construct a new LetterTokenizer using a given {@link org.apache.lucene.util.AttributeFactory}.
   *
   * @param factory the attribute factory to use for this {@link Tokenizer}
   * @param maxTokenLen maximum token length the tokenizer will emit. Must be greater than 0 and
   *     less than MAX_TOKEN_LENGTH_LIMIT (1024*1024)
   * @throws IllegalArgumentException if maxTokenLen is invalid.
   */
  public LetterTokenizer(AttributeFactory factory, int maxTokenLen) {
    super(factory, maxTokenLen);
  }

  /** Collects only characters which satisfy {@link Character#isLetter(int)}. */
  @Override
  protected boolean isTokenChar(int c) {
    return Character.isLetter(c);
  }
}