i have one small application for bank in java.
i run it from command prompt.
now i want that , when i run my programm from cmd prompt, 4 instances of it should run on 4 different cmd prompts.
they should be related to each other.
if i open one bank account in one window, it should reflect in onother window.
how can i do it.

wouldn't know how to do something like that, since when you're working in prompts, you'll propably have different applications (even when it are different instantiations of the same app) running

maybe you could use files that store the data you enter/use, and have threads in the program check for changes in them, to adjust the data it's currently working with, but I'll think this kind of sollution will soon lead to problems, as you should be able to read and write the same files by different applications at the same time.

maybe you should try to make a Swing application with different frames, would be a lot easier and in this way the different frames would be part of the same application.