Hi hao zhongzhi welcome to Javaranch , Apart from a few good books like the Head First Java, you'll need a lot of practice.Its theonly way to master not only Java but anything new. Practice well and you will learn well. [ September 18, 2008: Message edited by: Amit Ghorpade ]
Hi, Well Come to the world of Java and of course to JavaRanch.
Start with a book which gives the basics of Object Oriented Concepts. Most of the people start learning Java without these basic concepts which gives Java the best features of them all maintainability and flexibility. Go through some basic books on Java. Then I would advice you to completely go through Head First Java, Second Edition by Kathy and Bert.
I think this might help.
[ September 19, 2008: Message edited by: Sudipto Shekhar ]
Well as far as website, you have reached the correct place. You will find threads related to common as well as unique problems,all in here at Java Ranch.You can also find practice problems on Java right here.