Is there a way to send map data structures using MPJ

Question

Basically I am trying to send a hashmap using MPJ express. I haven't been able to find many useful examples of sending and receiving dictionary types with MPJ.

Using HashMap<String, Integer> frequencies = extract(rBuf); MPI.COMM_WORLD.Send(frequencies,0,1,MPI.OBJECT,0,1);

gives a "ClassCastException".