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,
* 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.
*/
import java.io.IOException;
import org.apache.lucene.index.IndexReader;
/** Expert: Calculate query weights and build query scorers.
* <p>
* The purpose of Weight is to make it so that searching does not modify
* a Query, so that a Query instance can be reused. <br>
* Searcher dependent state of the query should reside in the Weight. <br>
* IndexReader dependent state should reside in the Scorer.
* <p>
* A <code>Weight</code> is used in the following way:
* <ol>
* <li>A <code>Weight</code> is constructed by a top-level query,
* given a <code>Searcher</code> ({@link Query#createWeight(Searcher)}).
* <li>The {@link #sumOfSquaredWeights()} method is called
* on the <code>Weight</code> to compute
* the query normalization factor {@link Similarity#queryNorm(float)}
* of the query clauses contained in the query.
* <li>The query normalization factor is passed to {@link #normalize(float)}.
* At this point the weighting is complete.
* <li>A <code>Scorer</code> is constructed by {@link #scorer(IndexReader)}.
* </ol>
*/
public interface Weight extends java.io.Serializable {
/** The query that this concerns. */
Query getQuery();
/** The weight for this query. */
float getValue();
/** The sum of squared weights of contained query clauses. */
float sumOfSquaredWeights() throws IOException;
/** Assigns the query normalization factor to this. */
void normalize(float norm);
/** Constructs a scorer for this. */
Scorer scorer(IndexReader reader) throws IOException;
/** An explanation of the score computation for the named document. */
Explanation explain(IndexReader reader, int doc) throws IOException;
}
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