ever write a parallel processing program in java

Yes I have done this type of programs, they are called "multi threading" and Java supports multi threading. Also the platform on which your program is running should support multi threading. There are other progeamming languages also which support multithreading. In Java for making it able to run many processes parallelly we are required to create a thread (process) for each task and then manage the threads and multiple processes will run a same time thus making computation fast. This is a good feature of Java.

I haven't tried it. but refer this link(http://java.sys-con.com/read/419716_2.htm) It may help you

I have never written an application and takes a single task and breaks it down. But I have written plenty of applications that receive multiply tasks and processes them concurrently. What are you trying to do?

You are talking about a distributed programming model. This is not the same as multithreading. Almost any language that supports threading can do this. you can also do this with mpl.