I know that this is really bad game comparing to others, so please keep in mind: We (I - Lukáš Kubof, and the lead programmer - who didn't want his name to be associated with this game) were never making a game before in Java and for both of us it was the first game to ever develop.
The original plans were much more grander and even after a lot of changes to make the game easier to make, it wasn't enough. The last plans were to make a multiplayer game in which players shoot with the same button - leading to a lot of interesting and fun moments.
But it was too late so we just grabbed what we had - nothing, and made this in only one hour.