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.mapreduce.lib.partition; 020 021import org.apache.hadoop.classification.InterfaceAudience; 022import org.apache.hadoop.classification.InterfaceStability; 023import org.apache.hadoop.mapreduce.Partitioner; 024 025/** Partition keys by their {@link Object#hashCode()}. */ 026@InterfaceAudience.Public 027@InterfaceStability.Stable 028public class HashPartitioner<K, V> extends Partitioner<K, V> { 029 030 /** Use {@link Object#hashCode()} to partition. */ 031 public int getPartition(K key, V value, 032 int numReduceTasks) { 033 return (key.hashCode() & Integer.MAX_VALUE) % numReduceTasks; 034 } 035 036}