This is the project I have been posting all those questions for 
its finally in a semi-playable state with no goal, no waves, and only one mob and three towers. Rendered with just the Java Graphics library. This is a continuation of a tutorial I followed when I was first learning game design and I came back to it, completely changed the code and added many many things such a as a pause meny (press esc) and towers, an upgrading system, and a particle engine.
There is still a couple problems with the cannon targeting system and the images for the mob is still in progress, but remember its a work in progress game!
I would like some people to test it and tell me what I should tweak or add. Thanks!
P.S. Press ‘M’ for a little help