There are a number of different versions of Java each having their own focus. The main ones are
On top of all of that there are a very large number of additonal libraries you may wish to use. These include -
If you need to do something in Java then there is most likely a library somewhere which will already do it. All you will have to do is download it and use it! Yay!
Note - Do not confuse the term library and frame work. Frame works are designed to manage systems such as e-commerce websites. They will use libraries to achive their end. A frame work, such as struts, require you to understand the design princliples of the framework before you can make use of them. On the plus side they will save you programming time!