1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 package org.apache.giraph.aggregators; 20 21 import org.apache.hadoop.io.Writable; 22 23 /** 24 * Interface for Aggregator. Allows aggregate operations for all vertices 25 * in a given superstep. 26 * 27 * @param <A> Aggregated value 28 */ 29 public interface Aggregator<A extends Writable> { 30 /** 31 * Add a new value. 32 * Needs to be commutative and associative 33 * 34 * @param value Value to be aggregated. 35 */ 36 void aggregate(A value); 37 38 /** 39 * Return new aggregated value which is neutral to aggregate operation. 40 * Must be changeable without affecting internals of Aggregator 41 * 42 * @return Neutral value 43 */ 44 A createInitialValue(); 45 46 /** 47 * Return current aggregated value. 48 * Needs to be initialized if aggregate or setAggregatedValue 49 * have not been called before. 50 * 51 * @return Aggregated 52 */ 53 A getAggregatedValue(); 54 55 /** 56 * Set aggregated value. 57 * Can be used for initialization or reset. 58 * 59 * @param value Value to be set. 60 */ 61 void setAggregatedValue(A value); 62 63 /** 64 * Reset the value of aggregator to neutral value 65 */ 66 void reset(); 67 }