One of the most amazing Java books I have read to data is “How to think like a computer scientist”. It was written by a teacher who was frustrated with the complexities of normal coding books and decided to publish his own free book. It’s now been translate into many different coding languages.
Heads up though. There is only is really only one way to learn CS quickly, aka in 21 days.
(Comic by Abstruse Goose)
You have to keep willing to keep writing code everyday and get the experience of writing to truly learn it. Like learning any natural language, like Spanish, you actually have to sometimes “just do it” until you’re good at it. I would highly suggest focusing on writing clean understandable code that is well commented first, then learn about objects and methods.
Finally, take a look at this thread that I wrote to get some direction for writing code as well as teaching it. You (aka highschool students) are really motivated to work, you just sometimes need a little direction into what to work on. That may help to get a game plan. Feel free to PM me if you would like any help from 1646 with code. Good luck!