Note For Mr. Kiang: Figured out that last bug where enemies weren't appearing after awhile when you were playing the game.

I figured out why the enemies stopped appearing after awhile. While
debugging one last problem in my game, I commented out a line of code
and forgot to uncomment it again. If you want to just fix the version
of the game you have on your computer right now, you can go into the
gameframe package and find the class called GameFrame. Then look for
the manageObjects() method and find the line of code that is commented
out. Uncomment this line of code and the game should work properly
again. Alternatively, you can re-download the source files from GitHub
and re-import them into a new Eclipse project. Only import the folders
found in the "src" folder called "gameframe", "jgame", and "techdemo".
After these folders are imported, drag them into the src folder for you
project and then open up the GF_Tech_Demo class in the techdemo
package. Hit run and choose to run the program as an application. The
game should now work again.