PositionIncrementAttributeImpl.java

package com.antbrains.wordseg.luceneanalyzer;

/**
 * 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.
 */

/**
 * The positionIncrement determines the position of this token relative to the previous Token in a
 * {@link TokenStream}, used in phrase searching.
 *
 * <p>
 * The default value is one.
 *
 * <p>
 * Some common uses for this are:
 * <ul>
 *
 * <li>Set it to zero to put multiple terms in the same position. This is useful if, e.g., a word
 * has multiple stems. Searches for phrases including either stem will match. In this case, all but
 * the first stem's increment should be set to zero: the increment of the first instance should be
 * one. Repeating a token with an increment of zero can also be used to boost the scores of matches
 * on that token.
 *
 * <li>Set it to values greater than one to inhibit exact phrase matches. If, for example, one does
 * not want phrases to match across removed stop words, then one could build a stop word filter that
 * removes stop words and also sets the increment to the number of stop words removed before each
 * non-stop word. Then exact phrase queries will only match when the terms occur with no intervening
 * stop words.
 *
 * </ul>
 */
public class PositionIncrementAttributeImpl extends AttributeImpl implements
    PositionIncrementAttribute, Cloneable {
  private int positionIncrement = 1;

  /**
   * Set the position increment. The default value is one.
   *
   * @param positionIncrement
   *          the distance from the prior term
   */
  public void setPositionIncrement(int positionIncrement) {
    if (positionIncrement < 0)
      throw new IllegalArgumentException("Increment must be zero or greater: " + positionIncrement);
    this.positionIncrement = positionIncrement;
  }

  /**
   * Returns the position increment of this Token.
   * 
   * @see #setPositionIncrement
   */
  public int getPositionIncrement() {
    return positionIncrement;
  }

  @Override
  public void clear() {
    this.positionIncrement = 1;
  }

  @Override
  public boolean equals(Object other) {
    if (other == this) {
      return true;
    }

    if (other instanceof PositionIncrementAttributeImpl) {
      return positionIncrement == ((PositionIncrementAttributeImpl) other).positionIncrement;
    }

    return false;
  }

  @Override
  public int hashCode() {
    return positionIncrement;
  }

  @Override
  public void copyTo(AttributeImpl target) {
    PositionIncrementAttribute t = (PositionIncrementAttribute) target;
    t.setPositionIncrement(positionIncrement);
  }

}