I recommend following books/articles for reading:

• Thinking In Java - good starting point (plus available for free)
• Effective Java 2nd Edition by Joshua Bloch - good investment if you plan to undergo Java certification exams.

An article about a Java certification exam is here.

• Design Patterns - you should be familiar with design patters, so starting from Wikipedia is a good option
• Programming Video Games for the Evil Genius - make some fun games with this, and learn some Java as well. Good for programmers of all levels.
• Java Certification Preparation Guides - I strongly recommend EPractize Labs. They have all Java Certification preparation guides and training.lkn