001 package gate.creole.annic.apache.lucene.search;
002
003 /**
004 * Copyright 2002-2004 The Apache Software Foundation
005 *
006 * Licensed under the Apache License, Version 2.0 (the "License");
007 * you may not use this file except in compliance with the License.
008 * You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019 import java.io.IOException;
020
021 import java.util.HashSet;
022 import java.util.Iterator;
023
024 import gate.creole.annic.apache.lucene.index.IndexReader;
025
026 /** The abstract base class for queries.
027 <p>Instantiable subclasses are:
028 <ul>
029 <li> {@link TermQuery}
030 <li> {@link BooleanQuery}
031 <li> {@link PhraseQuery}
032 </ul>
033 <p>A parser for queries is contained in:
034 <ul>
035 <li>{@link gate.creole.annic.apache.lucene.queryParser.QueryParser QueryParser}
036 </ul>
037 */
038 public abstract class Query implements java.io.Serializable, Cloneable {
039 private float boost = 1.0f; // query boost factor
040
041 /** Sets the boost for this query clause to <code>b</code>. Documents
042 * matching this clause will (in addition to the normal weightings) have
043 * their score multiplied by <code>b</code>.
044 */
045 public void setBoost(float b) { boost = b; }
046
047 /** Gets the boost for this clause. Documents matching
048 * this clause will (in addition to the normal weightings) have their score
049 * multiplied by <code>b</code>. The boost is 1.0 by default.
050 */
051 public float getBoost() { return boost; }
052
053 /** Prints a query to a string, with <code>field</code> as the default field
054 * for terms. <p>The representation used is one that is readable by
055 * {@link gate.creole.annic.apache.lucene.queryParser.QueryParser QueryParser}
056 * (although, if the query was created by the parser, the printed
057 * representation may not be exactly what was parsed).
058 */
059 public abstract String toString(String field);
060
061 /** Prints a query to a string. */
062 public String toString() {
063 return toString("");
064 }
065
066 /** Expert: Constructs an appropriate Weight implementation for this query.
067 *
068 * <p>Only implemented by primitive queries, which re-write to themselves.
069 */
070 protected Weight createWeight(Searcher searcher) {
071 throw new UnsupportedOperationException();
072 }
073
074 /** Expert: Constructs an initializes a Weight for a top-level query. */
075 public Weight weight(Searcher searcher)
076 throws IOException {
077 Query query = searcher.rewrite(this);
078 Weight weight = query.createWeight(searcher);
079 float sum = weight.sumOfSquaredWeights();
080 float norm = getSimilarity(searcher).queryNorm(sum);
081 weight.normalize(norm);
082 return weight;
083 }
084
085 /** Expert: called to re-write queries into primitive queries. */
086 public Query rewrite(IndexReader reader) throws IOException {
087 return this;
088 }
089
090 /** Expert: called when re-writing queries under MultiSearcher.
091 *
092 * <p>Only implemented by derived queries, with no
093 * {@link #createWeight(Searcher)} implementatation.
094 */
095 public Query combine(Query[] queries) {
096 throw new UnsupportedOperationException();
097 }
098
099
100 /** Expert: merges the clauses of a set of BooleanQuery's into a single
101 * BooleanQuery.
102 *
103 *<p>A utility for use by {@link #combine(Query[])} implementations.
104 */
105 public static Query mergeBooleanQueries(Query[] queries) {
106 HashSet allClauses = new HashSet();
107 for (int i = 0; i < queries.length; i++) {
108 BooleanClause[] clauses = ((BooleanQuery)queries[i]).getClauses();
109 for (int j = 0; j < clauses.length; j++) {
110 allClauses.add(clauses[j]);
111 }
112 }
113
114 BooleanQuery result = new BooleanQuery();
115 Iterator i = allClauses.iterator();
116 while (i.hasNext()) {
117 result.add((BooleanClause)i.next());
118 }
119 return result;
120 }
121
122 /** Expert: Returns the Similarity implementation to be used for this query.
123 * Subclasses may override this method to specify their own Similarity
124 * implementation, perhaps one that delegates through that of the Searcher.
125 * By default the Searcher's Similarity implementation is returned.*/
126 public Similarity getSimilarity(Searcher searcher) {
127 return searcher.getSimilarity();
128 }
129
130 /** Returns a clone of this query. */
131 public Object clone() {
132 try {
133 return (Query)super.clone();
134 } catch (CloneNotSupportedException e) {
135 throw new RuntimeException("Clone not supported: " + e.getMessage());
136 }
137 }
138 }
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