How can two programs talk to each other in Java?

Programmer Question

I want to ‪reduce‬ the CPU usage/ROM usage/RAM usage - generally‬, all system resources that my app uses - who doesn't? :)

For this reason I want to split the preferences window from the rest of the application,
and let the preferences window to run as ‪independent‬ program.

The preferences program ‪should‬ write to a Property file(not a problem at all) and to send a "update signal" to the main program - which means it should call the update method (that i wrote) that found in the Main class.

How can I call the update method in the Main program from the preferences program?

To put it another way, is a way to build preferences window that take system resources just when the window appears?

Is this approach - of separating programs and let them talk to each other (somehow) - the right approach for speeding up my programs?

Find the answer here