JAVA: Create Events as a separate program...Is it possible?

I'm an intermediate 开发者_如何学JAVAin using java and my professor gave me a project to create a GUI calculator. He wants the main, numbers GUI, operations GUI, C/CE/= GUI, and events handling to be in separate programs. I was able to make the GUI parts but i'm having trouble throwing events for each of them. Can anyone give me any pointers in how to throw events from one GUI program to another?

Here are the programs for my calculator...

http://www.mediafire.com/?9c9feallvg9c53h

You can use a pipe or a socket between the processes and send some data in it using some custom protocol: send '+' when the '+' was pressed or whatever.