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package org.apache.lucene.search;
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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import java.io.IOException;
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import java.util.PriorityQueue;
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import org.apache.lucene.index.IndexReader;
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import org.apache.lucene.index.Term;
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* Base rewrite method for collecting only the top terms
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* via a priority queue.
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* @lucene.internal Only public to be accessible by spans package.
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public abstract class TopTermsRewrite<Q extends Query> extends TermCollectingRewrite<Q> {
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private final int size;
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* Create a TopTermsBooleanQueryRewrite for
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* at most <code>size</code> terms.
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* NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than
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* <code>size</code>, then it will be used instead.
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public TopTermsRewrite(int size) {
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/** return the maximum priority queue size */
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public int getSize() {
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/** return the maximum size of the priority queue (for boolean rewrites this is BooleanQuery#getMaxClauseCount). */
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protected abstract int getMaxSize();
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public Q rewrite(final IndexReader reader, final MultiTermQuery query) throws IOException {
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final int maxSize = Math.min(size, getMaxSize());
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final PriorityQueue<ScoreTerm> stQueue = new PriorityQueue<ScoreTerm>();
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collectTerms(reader, query, new TermCollector() {
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public boolean collect(Term t, float boost) {
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// ignore uncompetitive hits
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if (stQueue.size() >= maxSize && boost <= stQueue.peek().boost)
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// add new entry in PQ
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// possibly drop entries from queue
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st = (stQueue.size() > maxSize) ? stQueue.poll() : new ScoreTerm();
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private ScoreTerm st = new ScoreTerm();
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final Q q = getTopLevelQuery();
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for (final ScoreTerm st : stQueue) {
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addClause(q, st.term, query.getBoost() * st.boost); // add to query
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query.incTotalNumberOfTerms(stQueue.size());
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public int hashCode() {
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public boolean equals(Object obj) {
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if (this == obj) return true;
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if (obj == null) return false;
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if (getClass() != obj.getClass()) return false;
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final TopTermsRewrite other = (TopTermsRewrite) obj;
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if (size != other.size) return false;
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private static class ScoreTerm implements Comparable<ScoreTerm> {
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public int compareTo(ScoreTerm other) {
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if (this.boost == other.boost)
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return other.term.compareTo(this.term);
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return Float.compare(this.boost, other.boost);