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DoubleOverwriteAggregator xref
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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  
19  package org.apache.giraph.aggregators;
20  
21  import org.apache.hadoop.io.DoubleWritable;
22  
23  /**
24   * Aggregator that stores a value that is overwritten once another value is
25   * aggregated. This aggregator is useful for one-to-many communication from
26   * master.compute() or from a special vertex. In case multiple vertices write
27   * to this aggregator, its behavior is non-deterministic.
28   */
29  public class DoubleOverwriteAggregator extends
30      BasicAggregator<DoubleWritable> {
31    @Override
32    public void aggregate(DoubleWritable value) {
33      getAggregatedValue().set(value.get());
34    }
35  
36    @Override
37    public DoubleWritable createInitialValue() {
38      return new DoubleWritable(0);
39    }
40  }