1) Get familiar with java basics - syntax, variables defs , arrays, control loops. Run simple examples from the command line using a single Class with a main method.
2) Get a taste of Object Oriented Programming with Java. I think just a small introduction to understand Classes, Class instances, methods. Go back to the exercises in #1 and try to spread you code across multiple Classes ( One class definition per .java file should be sufficient)
After you've completed the above steps, you should have enough Java under your belt and may be ready to move on beyond the command line.
For FRC Teams this may be the next step.
https://wpilib.screenstepslive.com/s/4485/m/13809