Map output value different from Reduce Output value

[Dennis Kubes]

How would I set the map output value class to be different from the 
reduce output value class.  I am trying the code below but it doesn't 
seem to work.  It throws an error saying WordWeights is not 
ObjectWritable where word weights is my final output value class.

...
   rovejob.setMapOutputValueClass(ObjectWritable.class);
   rovejob.setOutputFormat(MapFileOutputFormat.class);
   rovejob.setOutputKeyClass(UTF8.class);   
   rovejob.setOutputValueClass(WordWeights.class);

Dennis