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    
019    package org.apache.hadoop.mapreduce.lib.aggregate;
020    
021    import java.util.ArrayList;
022    
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import org.apache.hadoop.classification.InterfaceStability;
025    
026    /**
027     * This class implements a value aggregator that maintain the minimum of 
028     * a sequence of long values.
029     * 
030     */
031    @InterfaceAudience.Public
032    @InterfaceStability.Stable
033    public class LongValueMin implements ValueAggregator<String> {
034    
035      long minVal = Long.MAX_VALUE;
036        
037      /**
038       *  the default constructor
039       *
040       */
041      public LongValueMin() {
042        reset();
043      }
044    
045      /**
046       * add a value to the aggregator
047       * 
048       * @param val
049       *          an object whose string representation represents a long value.
050       * 
051       */
052      public void addNextValue(Object val) {
053        long newVal = Long.parseLong(val.toString());
054        if (this.minVal > newVal) {
055          this.minVal = newVal;
056        }
057      }
058        
059      /**
060       * add a value to the aggregator
061       * 
062       * @param newVal
063       *          a long value.
064       * 
065       */
066      public void addNextValue(long newVal) {
067        if (this.minVal > newVal) {
068          this.minVal = newVal;
069        };
070      }
071        
072      /**
073       * @return the aggregated value
074       */
075      public long getVal() {
076        return this.minVal;
077      }
078        
079      /**
080       * @return the string representation of the aggregated value
081       */
082      public String getReport() {
083        return ""+minVal;
084      }
085    
086      /**
087       * reset the aggregator
088       */
089      public void reset() {
090        minVal = Long.MAX_VALUE;
091      }
092    
093      /**
094       * @return return an array of one element. The element is a string
095       *         representation of the aggregated value. The return value is
096       *         expected to be used by the a combiner.
097       */
098      public ArrayList<String> getCombinerOutput() {
099        ArrayList<String> retv = new ArrayList<String>(1);
100        retv.add(""+minVal);
101        return retv;
102      }
103    }