我以为他们指的是Reducer但在我的程序中我有publicstaticclassMyMapperextendsMapper和publicstaticclassMyReducerextendsReducer如果我有job.setOutputKeyClass(NullWritable.class);job.setOutputValueClass(Text.class);我得到以下异常Typemismatchinkeyfrommap:expectedorg.apache.hadoop.io.NullWritable,recievedorg.apache.hadoop.io.Text但如果我

驱动代码:publicclassWcDriver{publicstaticvoidmain(String[]args)throwsIOException,InterruptedException,ClassNotFoundException{Configurationconf=newConfiguration();Jobjob=newJob(conf,"WcDriver");job.setJarByClass(WcDriver.class);job.setOutputKeyClass(Text.class);job.setOutputValueClass(LongWritable.cl