Each game is made of some objects. These can be images, or sounds, but also complex structures, such as a game character and its abilities. In our game, we have a few objects, as follows:
The cities we have to defend
The rocket launchers that will fire our rockets
The rockets themselves
The bombs that will fall down on our precious cities and try to destroy them
Explosions that will show up once a rocket bursts into pieces (the particle clouds from these explosions will be the real harm to the bombs; if they collide with an explosion cloud, the bombs will be destroyed)
There are few more elements/objects to the game, such as the game UI (score, background, and so on), but we will concentrate on the ones just listed. Each object will be built with a separate class.