Defending your castle is simpler than history might have you believe. Simply position your mouse over an enemy troop and use the left-mouse button to pick him up. Make a throwing motion with the mouse, releasing the button to fling your unfortunate victim through the air.
Defend Your Castle takes place on a grassy plain surrounded by invaders.
GameCanvas is a Canvas with additional capabilities; it provides methods for immediate painting and for examining the state of the device keys. These new methods make it possible to enclose all of a game's functionality in a single loop, under control of a single thread. To see why this is attractive, think about how you would implement a typical game using Canvas: