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 smallest of 
028     * a sequence of strings.
029     * 
030     */
031    @InterfaceAudience.Public
032    @InterfaceStability.Stable
033    public class StringValueMin implements ValueAggregator<String> {
034    
035      String minVal = null;
036        
037      /**
038       *  the default constructor
039       *
040       */
041      public StringValueMin() {
042        reset();
043      }
044    
045      /**
046       * add a value to the aggregator
047       * 
048       * @param val
049       *          a string.
050       * 
051       */
052      public void addNextValue(Object val) {
053        String newVal = val.toString();
054        if (this.minVal == null || this.minVal.compareTo(newVal) > 0) {
055          this.minVal = newVal;
056        }
057      }
058        
059        
060      /**
061       * @return the aggregated value
062       */
063      public String getVal() {
064        return this.minVal;
065      }
066        
067      /**
068       * @return the string representation of the aggregated value
069       */
070      public String getReport() {
071        return minVal;
072      }
073    
074      /**
075       * reset the aggregator
076       */
077      public void reset() {
078        minVal = null;
079      }
080    
081      /**
082       * @return return an array of one element. The element is a string
083       *         representation of the aggregated value. The return value is
084       *         expected to be used by the a combiner.
085       */
086      public ArrayList<String> getCombinerOutput() {
087        ArrayList<String> retv = new ArrayList<String>(1);
088        retv.add(minVal);
089        return retv;
090      }
091    }