It doesn't seem that image files -> "64px-SpaceInvadersLaserDepiction.png" & "j4bc.gif"
are accessible from that link!

Also, if you wanna some code to happen only when a user presses a key,
put that code inside functions keyPressed() & keyReleased(),
rather than checking variable keyPressed all the time!

Check it out program MultipleBullets @ this post,
to see how to do it!