/** * Copyright 2005 The Apache Software Foundation * * Licensed 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.hadoop.mapred;import org.apache.hadoop.io.Writable;import org.apache.hadoop.io.WritableComparable;/** Partitions the key space.  A partition is created for each reduce task. */public interface Partitioner extends JobConfigurable {  /** Returns the paritition number for a given entry given the total number of   * partitions.  Typically a hash function on a all or a subset of the key.   *   * @param key the entry key   * @param value the entry value   * @param numPartitions the number of partitions   * @return the partition number   */  int getPartition(WritableComparable key, Writable value, int numPartitions);}