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Lucene example source code file (DisjunctionMaxQuery.java)

This example Lucene source code file (DisjunctionMaxQuery.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

arraylist, complexexplanation, disjunctionmaxquery, disjunctionmaxquery, disjunctionmaxweight, explanation, io, ioexception, ioexception, override, override, query, query, scorer, util, weight

The Lucene DisjunctionMaxQuery.java source code

package org.apache.lucene.search;

 * Copyright 2004 The Apache Software Foundation
 * Licensed 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,
 * See the License for the specific language governing permissions and
 * limitations under the License.

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;

 * A query that generates the union of documents produced by its subqueries, and that scores each document with the maximum
 * score for that document as produced by any subquery, plus a tie breaking increment for any additional matching subqueries.
 * This is useful when searching for a word in multiple fields with different boost factors (so that the fields cannot be
 * combined equivalently into a single search field).  We want the primary score to be the one associated with the highest boost,
 * not the sum of the field scores (as BooleanQuery would give).
 * If the query is "albino elephant" this ensures that "albino" matching one field and "elephant" matching
 * another gets a higher score than "albino" matching both fields.
 * To get this result, use both BooleanQuery and DisjunctionMaxQuery:  for each term a DisjunctionMaxQuery searches for it in
 * each field, while the set of these DisjunctionMaxQuery's is combined into a BooleanQuery.
 * The tie breaker capability allows results that include the same term in multiple fields to be judged better than results that
 * include this term in only the best of those multiple fields, without confusing this with the better case of two different terms
 * in the multiple fields.
public class DisjunctionMaxQuery extends Query implements Iterable<Query> {

  /* The subqueries */
  private ArrayList<Query> disjuncts = new ArrayList();

  /* Multiple of the non-max disjunct scores added into our final score.  Non-zero values support tie-breaking. */
  private float tieBreakerMultiplier = 0.0f;

  /** Creates a new empty DisjunctionMaxQuery.  Use add() to add the subqueries.
   * @param tieBreakerMultiplier the score of each non-maximum disjunct for a document is multiplied by this weight
   *        and added into the final score.  If non-zero, the value should be small, on the order of 0.1, which says that
   *        10 occurrences of word in a lower-scored field that is also in a higher scored field is just as good as a unique
   *        word in the lower scored field (i.e., one that is not in any higher scored field.
  public DisjunctionMaxQuery(float tieBreakerMultiplier) {
    this.tieBreakerMultiplier = tieBreakerMultiplier;

   * Creates a new DisjunctionMaxQuery
   * @param disjuncts a Collection<Query> of all the disjuncts to add
   * @param tieBreakerMultiplier   the weight to give to each matching non-maximum disjunct
  public DisjunctionMaxQuery(Collection<Query> disjuncts, float tieBreakerMultiplier) {
    this.tieBreakerMultiplier = tieBreakerMultiplier;

  /** Add a subquery to this disjunction
   * @param query the disjunct added
  public void add(Query query) {

  /** Add a collection of disjuncts to this disjunction
   * via Iterable<Query>
  public void add(Collection<Query> disjuncts) {

  /** An Iterator<Query> over the disjuncts */
  public Iterator<Query> iterator() {
    return disjuncts.iterator();

   * Expert: the Weight for DisjunctionMaxQuery, used to
   * normalize, score and explain these queries.
   * <p>NOTE: this API and implementation is subject to
   * change suddenly in the next release.</p>
  protected class DisjunctionMaxWeight extends Weight {
    /** The Similarity implementation. */
    protected Similarity similarity;

    /** The Weights for our subqueries, in 1-1 correspondence with disjuncts */
    protected ArrayList<Weight> weights = new ArrayList();  // The Weight's for our subqueries, in 1-1 correspondence with disjuncts

    /** Construct the Weight for this Query searched by searcher.  Recursively construct subquery weights. */
    public DisjunctionMaxWeight(Searcher searcher) throws IOException {
      this.similarity = searcher.getSimilarity();
      for (Query disjunctQuery : disjuncts) {

    /** Return our associated DisjunctionMaxQuery */
    public Query getQuery() { return DisjunctionMaxQuery.this; }

    /** Return our boost */
    public float getValue() { return getBoost(); }

    /** Compute the sub of squared weights of us applied to our subqueries.  Used for normalization. */
    public float sumOfSquaredWeights() throws IOException {
      float max = 0.0f, sum = 0.0f;
      for (Weight currentWeight : weights) {
        float sub = currentWeight.sumOfSquaredWeights();
        sum += sub;
        max = Math.max(max, sub);
      float boost = getBoost();
      return (((sum - max) * tieBreakerMultiplier * tieBreakerMultiplier) + max) * boost * boost;

    /** Apply the computed normalization factor to our subqueries */
    public void normalize(float norm) {
      norm *= getBoost();  // Incorporate our boost
      for (Weight wt : weights) {

    /** Create the scorer used to score our associated DisjunctionMaxQuery */
    public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder,
        boolean topScorer) throws IOException {
      Scorer[] scorers = new Scorer[weights.size()];
      int idx = 0;
      for (Weight w : weights) {
        Scorer subScorer = w.scorer(reader, true, false);
        if (subScorer != null && subScorer.nextDoc() != DocIdSetIterator.NO_MORE_DOCS) {
          scorers[idx++] = subScorer;
      if (idx == 0) return null; // all scorers did not have documents
      DisjunctionMaxScorer result = new DisjunctionMaxScorer(this, tieBreakerMultiplier, similarity, scorers, idx);
      return result;

    /** Explain the score we computed for doc */
    public Explanation explain(IndexReader reader, int doc) throws IOException {
      if (disjuncts.size() == 1) return weights.get(0).explain(reader,doc);
      ComplexExplanation result = new ComplexExplanation();
      float max = 0.0f, sum = 0.0f;
      result.setDescription(tieBreakerMultiplier == 0.0f ? "max of:" : "max plus " + tieBreakerMultiplier + " times others of:");
      for (Weight wt : weights) {
        Explanation e = wt.explain(reader, doc);
        if (e.isMatch()) {
          sum += e.getValue();
          max = Math.max(max, e.getValue());
      result.setValue(max + (sum - max) * tieBreakerMultiplier);
      return result;
  }  // end of DisjunctionMaxWeight inner class

  /** Create the Weight used to score us */
  public Weight createWeight(Searcher searcher) throws IOException {
    return new DisjunctionMaxWeight(searcher);

  /** Optimize our representation and our subqueries representations
   * @param reader the IndexReader we query
   * @return an optimized copy of us (which may not be a copy if there is nothing to optimize) */
  public Query rewrite(IndexReader reader) throws IOException {
    int numDisjunctions = disjuncts.size();
    if (numDisjunctions == 1) {
      Query singleton = disjuncts.get(0);
      Query result = singleton.rewrite(reader);
      if (getBoost() != 1.0f) {
        if (result == singleton) result = (Query)result.clone();
        result.setBoost(getBoost() * result.getBoost());
      return result;
    DisjunctionMaxQuery clone = null;
    for (int i = 0 ; i < numDisjunctions; i++) {
      Query clause = disjuncts.get(i);
      Query rewrite = clause.rewrite(reader);
      if (rewrite != clause) {
        if (clone == null) clone = (DisjunctionMaxQuery)this.clone();
        clone.disjuncts.set(i, rewrite);
    if (clone != null) return clone;
    else return this;

  /** Create a shallow copy of us -- used in rewriting if necessary
   * @return a copy of us (but reuse, don't copy, our subqueries) */
  @Override @SuppressWarnings("unchecked")
  public Object clone() {
    DisjunctionMaxQuery clone = (DisjunctionMaxQuery)super.clone();
    clone.disjuncts = (ArrayList<Query>) this.disjuncts.clone();
    return clone;

  // inherit javadoc
  public void extractTerms(Set<Term> terms) {
    for (Query query : disjuncts) {

  /** Prettyprint us.
   * @param field the field to which we are applied
   * @return a string that shows what we do, of the form "(disjunct1 | disjunct2 | ... | disjunctn)^boost"
  public String toString(String field) {
    StringBuilder buffer = new StringBuilder();
    int numDisjunctions = disjuncts.size();
    for (int i = 0 ; i < numDisjunctions; i++) {
      Query subquery = disjuncts.get(i);
      if (subquery instanceof BooleanQuery) {   // wrap sub-bools in parens
      else buffer.append(subquery.toString(field));
      if (i != numDisjunctions-1) buffer.append(" | ");
    if (tieBreakerMultiplier != 0.0f) {
    if (getBoost() != 1.0) {
    return buffer.toString();

  /** Return true iff we represent the same query as o
   * @param o another object
   * @return true iff o is a DisjunctionMaxQuery with the same boost and the same subqueries, in the same order, as us
  public boolean equals(Object o) {
    if (! (o instanceof DisjunctionMaxQuery) ) return false;
    DisjunctionMaxQuery other = (DisjunctionMaxQuery)o;
    return this.getBoost() == other.getBoost()
            && this.tieBreakerMultiplier == other.tieBreakerMultiplier
            && this.disjuncts.equals(other.disjuncts);

  /** Compute a hash code for hashing us
   * @return the hash code
  public int hashCode() {
    return Float.floatToIntBits(getBoost())
            + Float.floatToIntBits(tieBreakerMultiplier)
            + disjuncts.hashCode();


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