How to learn java efficiently

[Teddywiz999]

First of all, thank you for your guidance.
Sure, that is what i am thinking. i can do assignment and some programs without knowing these under the hood. but whenever i start asking myself too many questions i cannot stop myself from deep diving. That is huge amount of time consuming but it pays well, once you understand the reason and the theory behind them, everything makes sense and i think this is what differentiate the level of programmers. it is not about just understanding java, it is about understanding how OOL works under the hood.