Java

ref doc

• http://howtodoinjava.com/ - how to do in java. A very good guy who share lots of his experience
• http://www.mkyong.com/ - Another site which you can find java dev experience
• http://www.careercup.com/ - career cup. A site you can find interview questions.

Singleton

• http://www.infoq.com/cn/articles/double-checked-locking-with-delay-initialization - singleton double check locking and lazy initialize
• http://en.wikipedia.org/wiki/Singleton_pattern#Lazy_initialization

difference between static synchronized method and non-static synchronized method

• The lock objects are difference between static synchronized method and non-static synchronized method. Static synchronized method lock object is class object (lock object: FooClass.class), non-static synchronized lock object is instance object (lock object: )