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
019package org.apache.hadoop.mapred.lib;
020
021import org.apache.hadoop.classification.InterfaceAudience;
022import org.apache.hadoop.classification.InterfaceStability;
023import org.apache.hadoop.mapred.Partitioner;
024import org.apache.hadoop.mapred.JobConf;
025
026/** 
027 * Partition keys by their {@link Object#hashCode()}. 
028 */
029@InterfaceAudience.Public
030@InterfaceStability.Stable
031public 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}