Requesting code review on my game (so far) to see if I implemented it correctly

Hi all. I’ve been looking into learning game development over the past week and decided to just jump right in. I already have a few threads on the forum such as:

Can games like Super Meat Boy or Binding of Isaac be recreated with Java?

Need advice mapping out a plan/roadmap to follow for building a 2D platform game

And after a few days of reading and coding, what I’ve got to show for it is this:

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Now… what I’m asking for is maybe some of you can take a look at how I did what I did and suggest if I could implement it better. I’m asking because I don’t think it’s good programming practice to just develop haphazardly as long as your program works. I think that there’s still a right way to do things, is what I’m saying. Here’s my code:

main class - http://www.java-gaming.org/?action=pastebin&id=566
Barrier class - http://www.java-gaming.org/?action=pastebin&id=567
Ball class - http://www.java-gaming.org/?action=pastebin&id=568

Questions / Comments:

(1) I’ve seen some tutorials such as this that put the entire physics world into another class. Is that really recommendable? If so, how do I tweak my current code to turn it into that?

(2) Are button names for all gamepads standard? asking because I don’t know if it’s correct that I use “.equals(“X Axis”)”, “.equals(“Y Axis”)” and “.equals(“Button 0”)” to detect inputs from the left analog stick and A-button respectively.

(3) I’m pretty sure I’m not implementing collision detection quite right at all (see createCollisionListener()). Seems like a brute-force way to go about the logic - with the use of getUserData()/setUserData() - which I’ll have to revisit.

That’s all I can think of now. If anyone has the time and patience to take a look at the code, thanks in advance!