java.lang.Exception: java.lang.RuntimeException:
java.lang.NoSuchMethodException: Hadoop_FPTree$SumMapper.<init>() at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:403) Caused by: java.lang.RuntimeException: java.lang.NoSuchMethodException: Hadoop_FPTree$SumMapper.<init>() at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:131)
Mapper和Reducer作为内部类必须是静态static的。另外，他们可以作为同级的类。
java.lang.Exception: java.lang.ClassCastException:
org.apache.hadoop.io.LongWritable cannot be cast to org.apache.hadoop.io.IntWritable at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:403)
Mapper默认的输入是 <位置 文本值> 位置时候LongWritable类型
原文：http://www.cnblogs.com/manhua/p/3538372.html