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The best method to learn Java is to do a little bit each day. If you can't figure something out, leave it for a few hours or longer and then come back to take a fresh look.

And as always, if...

Mmm... depends on what you mean by "learn" java. I picked up the basic Syntax and some OOP concepts in maybe a few weeks to a few months, but that's because i've had a few years of other programming...