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package org.apache.lucene.search;
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* Copyright 2004 The Apache Software Foundation
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* 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.ArrayList;
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import java.util.Collection;
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import java.util.Iterator;
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import org.apache.lucene.index.IndexReader;
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import org.apache.lucene.index.Term;
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* A query that generates the union of documents produced by its subqueries, and that scores each document with the maximum
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* score for that document as produced by any subquery, plus a tie breaking increment for any additional matching subqueries.
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* This is useful when searching for a word in multiple fields with different boost factors (so that the fields cannot be
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* combined equivalently into a single search field). We want the primary score to be the one associated with the highest boost,
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* not the sum of the field scores (as BooleanQuery would give).
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* If the query is "albino elephant" this ensures that "albino" matching one field and "elephant" matching
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* another gets a higher score than "albino" matching both fields.
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* To get this result, use both BooleanQuery and DisjunctionMaxQuery: for each term a DisjunctionMaxQuery searches for it in
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* each field, while the set of these DisjunctionMaxQuery's is combined into a BooleanQuery.
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* The tie breaker capability allows results that include the same term in multiple fields to be judged better than results that
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* include this term in only the best of those multiple fields, without confusing this with the better case of two different terms
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* in the multiple fields.
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public class DisjunctionMaxQuery extends Query implements Iterable<Query> {
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private ArrayList<Query> disjuncts = new ArrayList<Query>();
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/* Multiple of the non-max disjunct scores added into our final score. Non-zero values support tie-breaking. */
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private float tieBreakerMultiplier = 0.0f;
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/** Creates a new empty DisjunctionMaxQuery. Use add() to add the subqueries.
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* @param tieBreakerMultiplier the score of each non-maximum disjunct for a document is multiplied by this weight
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* and added into the final score. If non-zero, the value should be small, on the order of 0.1, which says that
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* 10 occurrences of word in a lower-scored field that is also in a higher scored field is just as good as a unique
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* word in the lower scored field (i.e., one that is not in any higher scored field.
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public DisjunctionMaxQuery(float tieBreakerMultiplier) {
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this.tieBreakerMultiplier = tieBreakerMultiplier;
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* Creates a new DisjunctionMaxQuery
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* @param disjuncts a Collection<Query> of all the disjuncts to add
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* @param tieBreakerMultiplier the weight to give to each matching non-maximum disjunct
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public DisjunctionMaxQuery(Collection<Query> disjuncts, float tieBreakerMultiplier) {
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this.tieBreakerMultiplier = tieBreakerMultiplier;
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/** Add a subquery to this disjunction
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* @param query the disjunct added
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public void add(Query query) {
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/** Add a collection of disjuncts to this disjunction
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public void add(Collection<Query> disjuncts) {
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this.disjuncts.addAll(disjuncts);
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/** An Iterator<Query> over the disjuncts */
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public Iterator<Query> iterator() {
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return disjuncts.iterator();
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* Expert: the Weight for DisjunctionMaxQuery, used to
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* normalize, score and explain these queries.
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* <p>NOTE: this API and implementation is subject to
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* change suddenly in the next release.</p>
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protected class DisjunctionMaxWeight extends Weight {
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/** The Similarity implementation. */
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protected Similarity similarity;
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/** The Weights for our subqueries, in 1-1 correspondence with disjuncts */
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protected ArrayList<Weight> weights = new ArrayList<Weight>(); // The Weight's for our subqueries, in 1-1 correspondence with disjuncts
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/** Construct the Weight for this Query searched by searcher. Recursively construct subquery weights. */
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public DisjunctionMaxWeight(Searcher searcher) throws IOException {
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this.similarity = searcher.getSimilarity();
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for (Query disjunctQuery : disjuncts) {
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weights.add(disjunctQuery.createWeight(searcher));
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/** Return our associated DisjunctionMaxQuery */
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public Query getQuery() { return DisjunctionMaxQuery.this; }
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/** Return our boost */
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public float getValue() { return getBoost(); }
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/** Compute the sub of squared weights of us applied to our subqueries. Used for normalization. */
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public float sumOfSquaredWeights() throws IOException {
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float max = 0.0f, sum = 0.0f;
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for (Weight currentWeight : weights) {
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float sub = currentWeight.sumOfSquaredWeights();
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max = Math.max(max, sub);
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float boost = getBoost();
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return (((sum - max) * tieBreakerMultiplier * tieBreakerMultiplier) + max) * boost * boost;
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/** Apply the computed normalization factor to our subqueries */
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public void normalize(float norm) {
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norm *= getBoost(); // Incorporate our boost
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for (Weight wt : weights) {
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/** Create the scorer used to score our associated DisjunctionMaxQuery */
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public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder,
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boolean topScorer) throws IOException {
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Scorer[] scorers = new Scorer[weights.size()];
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for (Weight w : weights) {
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Scorer subScorer = w.scorer(reader, true, false);
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if (subScorer != null && subScorer.nextDoc() != DocIdSetIterator.NO_MORE_DOCS) {
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scorers[idx++] = subScorer;
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if (idx == 0) return null; // all scorers did not have documents
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DisjunctionMaxScorer result = new DisjunctionMaxScorer(this, tieBreakerMultiplier, similarity, scorers, idx);
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/** Explain the score we computed for doc */
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public Explanation explain(IndexReader reader, int doc) throws IOException {
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if (disjuncts.size() == 1) return weights.get(0).explain(reader,doc);
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ComplexExplanation result = new ComplexExplanation();
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float max = 0.0f, sum = 0.0f;
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result.setDescription(tieBreakerMultiplier == 0.0f ? "max of:" : "max plus " + tieBreakerMultiplier + " times others of:");
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for (Weight wt : weights) {
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Explanation e = wt.explain(reader, doc);
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result.setMatch(Boolean.TRUE);
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max = Math.max(max, e.getValue());
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result.setValue(max + (sum - max) * tieBreakerMultiplier);
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} // end of DisjunctionMaxWeight inner class
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/** Create the Weight used to score us */
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public Weight createWeight(Searcher searcher) throws IOException {
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return new DisjunctionMaxWeight(searcher);
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/** Optimize our representation and our subqueries representations
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* @param reader the IndexReader we query
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* @return an optimized copy of us (which may not be a copy if there is nothing to optimize) */
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public Query rewrite(IndexReader reader) throws IOException {
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int numDisjunctions = disjuncts.size();
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if (numDisjunctions == 1) {
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Query singleton = disjuncts.get(0);
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Query result = singleton.rewrite(reader);
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if (getBoost() != 1.0f) {
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if (result == singleton) result = (Query)result.clone();
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result.setBoost(getBoost() * result.getBoost());
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DisjunctionMaxQuery clone = null;
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for (int i = 0 ; i < numDisjunctions; i++) {
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Query clause = disjuncts.get(i);
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Query rewrite = clause.rewrite(reader);
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if (rewrite != clause) {
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if (clone == null) clone = (DisjunctionMaxQuery)this.clone();
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clone.disjuncts.set(i, rewrite);
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if (clone != null) return clone;
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/** Create a shallow copy of us -- used in rewriting if necessary
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* @return a copy of us (but reuse, don't copy, our subqueries) */
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@Override @SuppressWarnings("unchecked")
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public Object clone() {
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DisjunctionMaxQuery clone = (DisjunctionMaxQuery)super.clone();
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clone.disjuncts = (ArrayList<Query>) this.disjuncts.clone();
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public void extractTerms(Set<Term> terms) {
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for (Query query : disjuncts) {
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query.extractTerms(terms);
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* @param field the field to which we are applied
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* @return a string that shows what we do, of the form "(disjunct1 | disjunct2 | ... | disjunctn)^boost"
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public String toString(String field) {
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StringBuilder buffer = new StringBuilder();
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int numDisjunctions = disjuncts.size();
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for (int i = 0 ; i < numDisjunctions; i++) {
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Query subquery = disjuncts.get(i);
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if (subquery instanceof BooleanQuery) { // wrap sub-bools in parens
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buffer.append(subquery.toString(field));
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else buffer.append(subquery.toString(field));
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if (i != numDisjunctions-1) buffer.append(" | ");
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if (tieBreakerMultiplier != 0.0f) {
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buffer.append(tieBreakerMultiplier);
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if (getBoost() != 1.0) {
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buffer.append(getBoost());
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return buffer.toString();
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/** Return true iff we represent the same query as o
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* @param o another object
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* @return true iff o is a DisjunctionMaxQuery with the same boost and the same subqueries, in the same order, as us
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public boolean equals(Object o) {
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if (! (o instanceof DisjunctionMaxQuery) ) return false;
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DisjunctionMaxQuery other = (DisjunctionMaxQuery)o;
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return this.getBoost() == other.getBoost()
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&& this.tieBreakerMultiplier == other.tieBreakerMultiplier
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&& this.disjuncts.equals(other.disjuncts);
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/** Compute a hash code for hashing us
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* @return the hash code
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public int hashCode() {
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return Float.floatToIntBits(getBoost())
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+ Float.floatToIntBits(tieBreakerMultiplier)
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+ disjuncts.hashCode();