There are many excellent articles on Java Garbage Collection, Java Memory usage, and generally Java heap. Unfortunately, they are all over the place. They mix architecture, concepts, and problem solving as separate pieces. A lot of the material is out of date or doesn't include pragmatic information for solving problems with the garbage collector. E.g., pause times, heap space usage, etc.
In this post, I won't go into memory leaks. They're important but this is a different subject I would like to discuss in a post on its own.