001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  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    package org.apache.hadoop.mapred.lib;
020    
021    import org.apache.hadoop.classification.InterfaceAudience;
022    import org.apache.hadoop.classification.InterfaceStability;
023    import org.apache.hadoop.mapred.Partitioner;
024    import org.apache.hadoop.mapred.JobConf;
025    
026    /** 
027     * Partition keys by their {@link Object#hashCode()}. 
028     */
029    @InterfaceAudience.Public
030    @InterfaceStability.Stable
031    public class HashPartitioner<K2, V2> implements Partitioner<K2, V2> {
032    
033      public void configure(JobConf job) {}
034    
035      /** Use {@link Object#hashCode()} to partition. */
036      public int getPartition(K2 key, V2 value,
037                              int numReduceTasks) {
038        return (key.hashCode() & Integer.MAX_VALUE) % numReduceTasks;
039      }
040    
041    }