JAVA multithreading novice inquiry [closed]

We use threads only if we wish to do long computation tasks in the background.Main task is always the main thread.You can spawn other thread instances from it.you can make your second and third class runnable and use a thread to run them.In your case you need to wait for the threads to finish e.g only after retieval of your collections in your main thread,you can start the second thread and similarly you should wait for the second thread to complete before doing the third thread

There are two things that i can see you are worried about here and Java has two things to resolve them:

I am sure a lot of whats going on in your head wil be solved by this