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Lucene example source code file (ValueSource.java)

This example Lucene source code file (ValueSource.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

docvalues, docvalues, io, ioexception, override, override, serializable, serializable, string, string, valuesource

The Lucene ValueSource.java source code

package org.apache.lucene.search.function;

/**
 * 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.
 */

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.function.DocValues;

import java.io.IOException;
import java.io.Serializable;

/**
 * Expert: source of values for basic function queries.
 * <P>At its default/simplest form, values - one per doc - are used as the score of that doc.
 * <P>Values are instantiated as 
 * {@link org.apache.lucene.search.function.DocValues DocValues} for a particular reader.
 * <P>ValueSource implementations differ in RAM requirements: it would always be a factor
 * of the number of documents, but for each document the number of bytes can be 1, 2, 4, or 8. 
 *
 * @lucene.experimental
 *
 *
 */
public abstract class ValueSource implements Serializable {

  /**
   * Return the DocValues used by the function query.
   * @param reader the IndexReader used to read these values.
   * If any caching is involved, that caching would also be IndexReader based.  
   * @throws IOException for any error.
   */
  public abstract DocValues getValues(IndexReader reader) throws IOException;

  /** 
   * description of field, used in explain() 
   */
  public abstract String description();

  /* (non-Javadoc) @see java.lang.Object#toString() */
  @Override
  public String toString() {
    return description();
  }

  /**
   * Needed for possible caching of query results - used by {@link ValueSourceQuery#equals(Object)}.
   * @see Object#equals(Object)
   */
  @Override
  public abstract boolean equals(Object o);

  /**
   * Needed for possible caching of query results - used by {@link ValueSourceQuery#hashCode()}.
   * @see Object#hashCode()
   */
  @Override
  public abstract int hashCode();
  
}

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