how strong should be java for learning automation testing [on hold]

Have basic knowledge of java and want to learn automation testing. I am novice to automation and would like to know which part of java is basically used in automation (like threads, collections, etc), just to get an idea. And also would like to know if advance java is also used.

How long will it take to learn automation and what a person should have basic knowledge to learn it quickly.

Thanks in advance!!!