Java tutorial
/* * 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; } }