can any one over here tell me how to get the deep knowledge of java ... i ve done the core .... but still i lack in skill n understanding ...... n also i want to do certification in java so is there any free online certification n book which can clear every basic of me n has explained every thing very nicely n also have examples
Search in Google for some tutorials and pick the one from it you like the most.
To get a deep knowledge, you must exercise a lot of programming. No theory will help you. Get your hands on some programs. For example you can participate in an open-source project. The learing curve is very steep there, because first you see "professional" code where you can learn a lot from, and second if you make your own modifications on the code, you get feedback from other programmers how to improve. This way, you can save all your money for certifications and can even learn faster.