The following are some interesting, and possibly useful, online resources to help you in understanding Java programming and Java-related topics (like OOP).

Check them out!
Click on the following:
1. Sun's--The Java Tutorial
(Straight from the horse's mouth, the creators of Java--Sun Microsystems.)

2. Sun Java Developer--Java basics
(Another good tutorial from Sun)

3. Learn Java from the ground up
(Good stuff! A clear outline, and prepared as an easily digestible course.)

4. Java Application Developer Central
(Java Help! Technical, like a thirsty man drinking the ocean.)

5. FreewareJava.com
(Got a specific question/topic? Get a link to an answer/solution.)

6. Java Tutorial--Don't Fear the OOP
(Fun, educational, but hilarious! so...don't fear the OOP!)