Example solution

Here is a picture of what that whole object graph might look like when you are done. This is only to give you a sense of what you’re building, so you know if you’re on the right track — but don’t just copy this picture! Instead, work through the code and think it out for yourself, or the whole point of the activity is lost.

We put main()’s stack frame on a separate sheet of paper:

Here is a close-up with a new sheet of paper to represent the stack frame created when purchase() is called.

This image shows another new sheet of paper to represent the stack frame for deduct().

These images show the process of removing a call to deduct() once it has finished executing.

This is the same process happening after the call to purchase() has completed!

Here is what the state of your objects should look like when you’re done: