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

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Here is the source code for org.apache.lucene.search.PrefixQuery.java

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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 org.apache.lucene.index.Term;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.automaton.Automaton;

/** A Query that matches documents containing terms with a specified prefix. A PrefixQuery
 * is built by QueryParser for input like <code>app*</code>.
 *
 * <p>This query uses the {@link
 * MultiTermQuery#CONSTANT_SCORE_REWRITE}
 * rewrite method. */

public class PrefixQuery extends AutomatonQuery {

    /** Constructs a query for terms starting with <code>prefix</code>. */
    public PrefixQuery(Term prefix) {
        // It's OK to pass unlimited maxDeterminizedStates: the automaton is born small and determinized:
        super(prefix, toAutomaton(prefix.bytes()), Integer.MAX_VALUE, true);
        if (prefix == null) {
            throw new NullPointerException("prefix must not be null");
        }
    }

    /** Build an automaton accepting all terms with the specified prefix. */
    public static Automaton toAutomaton(BytesRef prefix) {
        final int numStatesAndTransitions = prefix.length + 1;
        final Automaton automaton = new Automaton(numStatesAndTransitions, numStatesAndTransitions);
        int lastState = automaton.createState();
        for (int i = 0; i < prefix.length; i++) {
            int state = automaton.createState();
            automaton.addTransition(lastState, state, prefix.bytes[prefix.offset + i] & 0xff);
            lastState = state;
        }
        automaton.setAccept(lastState, true);
        automaton.addTransition(lastState, lastState, 0, 255);
        automaton.finishState();
        assert automaton.isDeterministic();
        return automaton;
    }

    /** Returns the prefix of this query. */
    public Term getPrefix() {
        return term;
    }

    /** Prints a user-readable version of this query. */
    @Override
    public String toString(String field) {
        StringBuilder buffer = new StringBuilder();
        if (!getField().equals(field)) {
            buffer.append(getField());
            buffer.append(':');
        }
        buffer.append(term.text());
        buffer.append('*');
        return buffer.toString();
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = super.hashCode();
        result = prime * result + term.hashCode();
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (!super.equals(obj)) {
            return false;
        }
        // super.equals() ensures we are the same class
        PrefixQuery other = (PrefixQuery) obj;
        if (!term.equals(other.term)) {
            return false;
        }
        return true;
    }
}