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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  package org.apache.giraph.examples;
19  
20  import org.apache.giraph.graph.BasicComputation;
21  import org.apache.giraph.graph.Vertex;
22  import org.apache.hadoop.io.IntWritable;
23  import org.apache.hadoop.io.NullWritable;
24  
25  import java.io.IOException;
26  
27  /**
28   * Simple algorithm that computes the max value in the graph.
29   */
30  public class MaxComputation extends BasicComputation<IntWritable, IntWritable,
31      NullWritable, IntWritable> {
32    @Override
33    public void compute(Vertex<IntWritable, IntWritable, NullWritable> vertex,
34        Iterable<IntWritable> messages) throws IOException {
35      boolean changed = false;
36      for (IntWritable message : messages) {
37        if (vertex.getValue().get() < message.get()) {
38          vertex.setValue(message);
39          changed = true;
40        }
41      }
42      if (getSuperstep() == 0 || changed) {
43        sendMessageToAllEdges(vertex, vertex.getValue());
44      }
45      vertex.voteToHalt();
46    }
47  }