What should I do so that I can learn Java in a fast and efficient manner?

Perhaps you could audit a course. Auditing isn’t as expensive, but you’ll still get the instruction.

@snowberry some detailed description would be appreciated :)

I typically get a reference book from Amazon or B&N to start.

After that if I need more I sign up for an online course on O’Reilly Learning

If I had any good Java resources, I’d share them, but I tend to avoid Java, so I don’t.

The way I taught myself programming was to do my own little projects and experiments.

As a professional software developer, I have continued to use this general procedure:

Starting with a program I feel I fully understand, I change the code to see what it will do, and test some of my assumptions. Then I try to make the working program do different things, and see what I can get working a bit at a time, to add more and more things I knew how to do.

Then when I felt like I have enough useful things I know how to do to make something more complex, I outline what I want to try to make, and try to make that. Then I test it out to see if it actually works exactly as I expect or not, and if not, I study those parts so that I think I fully understand how to get them to work the way I want.

Sometimes lessons and examples are useful, but it depends strongly on who created them, and what the example is about. If I have time, I prefer to follow a set of gradual tutorials that build on each other, made by someone whose communication and teaching style I particularly like. Unfortunately, there are far more examples on the Internet of people with styles I don’t like, making very limited and barely-explained examples of doing things that aren’t what I really want to do, in some context that isn’t what I want or need.

I searched for “How to audit a college course”. This is the first link that popped up.
https://www.bestcolleges.com/blog/auditing-a-class/