org.apache.lucene.search.Query.java Source code

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/*
 * 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.
 */
package org.apache.lucene.search;

import java.io.IOException;

import org.apache.lucene.index.IndexReader;

/** The abstract base class for queries.
<p>Instantiable subclasses are:
<ul>
<li> {@link TermQuery}
<li> {@link BooleanQuery}
<li> {@link WildcardQuery}
<li> {@link PhraseQuery}
<li> {@link PrefixQuery}
<li> {@link MultiPhraseQuery}
<li> {@link FuzzyQuery}
<li> {@link RegexpQuery}
<li> {@link TermRangeQuery}
<li> {@link PointRangeQuery}
<li> {@link ConstantScoreQuery}
<li> {@link DisjunctionMaxQuery}
<li> {@link MatchAllDocsQuery}
</ul>
<p>See also the family of {@link org.apache.lucene.search.spans Span Queries}
   and additional queries available in the <a href="{@docRoot}/../queries/overview-summary.html">Queries module</a>
*/
public abstract class Query {

    /** Prints a query to a string, with <code>field</code> assumed to be the 
     * default field and omitted.
     */
    public abstract String toString(String field);

    /** Prints a query to a string. */
    @Override
    public final String toString() {
        return toString("");
    }

    /**
     * Expert: Constructs an appropriate Weight implementation for this query.
     * <p>
     * Only implemented by primitive queries, which re-write to themselves.
     *
     * @param scoreMode     How the produced scorers will be consumed.
     * @param boost         The boost that is propagated by the parent queries.
     */
    public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost) throws IOException {
        throw new UnsupportedOperationException("Query " + this + " does not implement createWeight");
    }

    /** Expert: called to re-write queries into primitive queries. For example,
     * a PrefixQuery will be rewritten into a BooleanQuery that consists
     * of TermQuerys.
     */
    public Query rewrite(IndexReader reader) throws IOException {
        return this;
    }

    /**
     * Recurse through the query tree, visiting any child queries
     * @param visitor a QueryVisitor to be called by each query in the tree
     */
    public void visit(QueryVisitor visitor) {
        visitor.visitLeaf(this);
    }

    /**
     * Override and implement query instance equivalence properly in a subclass. 
     * This is required so that {@link QueryCache} works properly.
     * 
     * Typically a query will be equal to another only if it's an instance of 
     * the same class and its document-filtering properties are identical that other
     * instance. Utility methods are provided for certain repetitive code. 
     * 
     * @see #sameClassAs(Object)
     * @see #classHash()
     */
    @Override
    public abstract boolean equals(Object obj);

    /**
     * Override and implement query hash code properly in a subclass. 
     * This is required so that {@link QueryCache} works properly.
     * 
     * @see #equals(Object)
     */
    @Override
    public abstract int hashCode();

    /**
     * Utility method to check whether <code>other</code> is not null and is exactly 
     * of the same class as this object's class.
     * 
     * When this method is used in an implementation of {@link #equals(Object)},
     * consider using {@link #classHash()} in the implementation
     * of {@link #hashCode} to differentiate different class
     */
    protected final boolean sameClassAs(Object other) {
        return other != null && getClass() == other.getClass();
    }

    private final int CLASS_NAME_HASH = getClass().getName().hashCode();

    /**
     * Provides a constant integer for a given class, derived from the name of the class.
     * The rationale for not using just {@link Class#hashCode()} is that classes may be
     * assigned different hash codes for each execution and we want hashes to be possibly
     * consistent to facilitate debugging.    
     */
    protected final int classHash() {
        return CLASS_NAME_HASH;
    }
}