Cool puzzle game, I like that it was written in Java. The puzzles got really hard really fast, maybe try to make some medium puzzles in-between?
Also, I didn't like how when you pushed an item, it moved but you didn't. I think you should make it so that you move to where the item was, and the item moves.
Also, this might just be me, but I don't like the [esc] to restart and [tab] to go back. I kept on finding myself pressing [z] and [r].
Otherwise, good job!