Debug

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

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 {
    }
}