hadoop StringValueMin 源码
haddop StringValueMin 代码
文件路径：/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/lib/aggregate/StringValueMin.java
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.mapreduce.lib.aggregate;
import java.util.ArrayList;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* This class implements a value aggregator that maintain the smallest of
* a sequence of strings.
*
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class StringValueMin implements ValueAggregator<String> {
String minVal = null;
/**
* the default constructor
*
*/
public StringValueMin() {
reset();
}
/**
* add a value to the aggregator
*
* @param val
* a string.
*
*/
public void addNextValue(Object val) {
String newVal = val.toString();
if (this.minVal == null || this.minVal.compareTo(newVal) > 0) {
this.minVal = newVal;
}
}
/**
* @return the aggregated value
*/
public String getVal() {
return this.minVal;
}
/**
* @return the string representation of the aggregated value
*/
public String getReport() {
return minVal;
}
/**
* reset the aggregator
*/
public void reset() {
minVal = null;
}
/**
* @return return an array of one element. The element is a string
* representation of the aggregated value. The return value is
* expected to be used by the a combiner.
*/
public ArrayList<String> getCombinerOutput() {
ArrayList<String> retv = new ArrayList<String>(1);
retv.add(minVal);
return retv;
}
}
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