一系列敌人，2D Java游戏

Basically, I am making a simple asteroids-y style side-scroller, I have had a little Java experience, but am not great when it comes to certain implementations. So, I want to create a bunch of asteroids that spawn at random times and at random y-positions. I figure the best way to do that is to do some sort of array, but I don't know how to really implement that, and do collision checking for the entire array. Here are relevant parts of my enemy and playing field classes.Basically, I am making a simple asteroids-y sty