= Debug =
{{{
#!java
public class HelloHadoop {

	public class HelloMapper extends
			Mapper<LongWritable, Text, LongWritable, Text> {
....
	}

	 public class HelloReducer extends
			Reducer<LongWritable, Text, LongWritable, Text> {
...
		}
	}

	public static void main(String[] args) throws IOException,
			InterruptedException, ClassNotFoundException {
    }
}
}}}

此一內部類別會引發
java.lang.RuntimeException: java.lang.NoSuchMethodException: WordIndex$wordindexM.<init>()

問題出在

宣告內部類別的  map 或 reduce 的class 前面沒有宣告 static public ，因此正確的應該如下

{{{
#!java
public class HelloHadoop {

	static public class HelloMapper extends
			Mapper<LongWritable, Text, LongWritable, Text> {
....
	}

	static public class HelloReducer extends
			Reducer<LongWritable, Text, LongWritable, Text> {
...
		}
	}

	public static void main(String[] args) throws IOException,
			InterruptedException, ClassNotFoundException {
    }
}
}}}