This is a very common question. You should search JavaRanch and/or the Web for answers.
The quick answer is that you cannot forcibly stop one running thread from another. You must not use the method Thread.stop(), as it is seriously broken. You must design and implement a way for the threads to cooperate in a shut-down procedure. The aforementioned search will show you a variety of ways that can be achieved.
Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.