This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Set yourself the challenge of making a game such as tic-tac-toe, quarto or even chess. Make your first task to be able to play the game through the console. Then try adding a GUI. You should also add multiplayer through LAN. Finally you can attempt writing a computer AI for the game.
You can learn a lot of different things from such a challenge. The project usually also becomes big enough that you have to learn how to structure it well.
The mind is a strange and wonderful thing. I'm not sure that it will ever be able to figure itself out, everything else, maybe. From the atom to the universe, everything, except itself.