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Lucene example source code file (DefaultSimilarity.java)

This example Lucene source code file (DefaultSimilarity.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

defaultsimilarity, defaultsimilarity, fieldinvertstate, fieldinvertstate, override, override, similarity, similarity

The Lucene DefaultSimilarity.java source code

package org.apache.lucene.search;

import org.apache.lucene.index.FieldInvertState;

/**
 * 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.
 */

/** Expert: Default scoring implementation. */
public class DefaultSimilarity extends Similarity {

  /** Implemented as
   *  <code>state.getBoost()*lengthNorm(numTerms), where
   *  <code>numTerms is {@link FieldInvertState#getLength()} if {@link
   *  #setDiscountOverlaps} is false, else it's {@link
   *  FieldInvertState#getLength()} - {@link
   *  FieldInvertState#getNumOverlap()}.
   *
   *  @lucene.experimental */
  @Override
  public float computeNorm(String field, FieldInvertState state) {
    final int numTerms;
    if (discountOverlaps)
      numTerms = state.getLength() - state.getNumOverlap();
    else
      numTerms = state.getLength();
    return state.getBoost() * ((float) (1.0 / Math.sqrt(numTerms)));
  }
  
  /** Implemented as <code>1/sqrt(sumOfSquaredWeights). */
  @Override
  public float queryNorm(float sumOfSquaredWeights) {
    return (float)(1.0 / Math.sqrt(sumOfSquaredWeights));
  }

  /** Implemented as <code>sqrt(freq). */
  @Override
  public float tf(float freq) {
    return (float)Math.sqrt(freq);
  }
    
  /** Implemented as <code>1 / (distance + 1). */
  @Override
  public float sloppyFreq(int distance) {
    return 1.0f / (distance + 1);
  }
    
  /** Implemented as <code>log(numDocs/(docFreq+1)) + 1. */
  @Override
  public float idf(int docFreq, int numDocs) {
    return (float)(Math.log(numDocs/(double)(docFreq+1)) + 1.0);
  }
    
  /** Implemented as <code>overlap / maxOverlap. */
  @Override
  public float coord(int overlap, int maxOverlap) {
    return overlap / (float)maxOverlap;
  }

  // Default true
  protected boolean discountOverlaps = true;

  /** Determines whether overlap tokens (Tokens with
   *  0 position increment) are ignored when computing
   *  norm.  By default this is true, meaning overlap
   *  tokens do not count when computing norms.
   *
   *  @lucene.experimental
   *
   *  @see #computeNorm
   */
  public void setDiscountOverlaps(boolean v) {
    discountOverlaps = v;
  }

  /** @see #setDiscountOverlaps */
  public boolean getDiscountOverlaps() {
    return discountOverlaps;
  }
}

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