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Update Hadoop-MapReduce.md

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@ -149,7 +149,7 @@ public class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritabl
`WordCountMapper`继承自`Mappe`r类，这是一个泛型类，定义如下：
`WordCountMapper`继承自`Mappe`类，这是一个泛型类，定义如下：
```java
WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable>
@ -162,13 +162,13 @@ public class Mapper<KEYIN, VALUEIN, KEYOUT, VALUEOUT> {
+ **KEYIN** : `mapping`输入key的类型，即每行的偏移量(每行第一个字符在整个文本中的位置)，`Long`类型，对应Hadoop中的`LongWritable`类型；
+ **VALUEIN** : `mapping`输入value的类型，即每行数据；`String`类型，对应Hadoop中`Text`类型；
+ **KEYOUT** ：`mapping`输出的key的类型，即每个单词；`String`类型，对应Hadoop中`Text`类型；
+ **VALUEOUT**：`mapping`输出value的类型，即每个单词出现的次数；这里用`int`类型，对应Hadoop中`IntWritable`类型。
+ **VALUEOUT**：`mapping`输出value的类型，即每个单词出现的次数；这里用`int`类型，对应`IntWritable`类型。
### 4.4 WordCountReducer
在Reduce中进程单词出现次数统计：
在Reduce中进行单词出现次数的统计：
```java
public class WordCountReducer extends Reducer<Text, IntWritable, Text, IntWritable> {