Killer Game Programming in Java

Defining the Bat

I'll define and implement the bat in the same way as the ball sprite. I'll write a textual specification of what a bat should do, translate it into a statechart, and then manually convert it into BatSprite, a subclass of Sprite. Once again, I'll refer to the ant sprite as a bat since that's what it does; that's why its class is BatSprite. The ant image is irrelevant to the game play since it could be anything.

Textual Specification

The bat can only move horizontally across the floor, controlled by arrow keys and mouse presses. Once the bat is set in motion, it continues moving until its direction is changed or it is stopped. As the bat leaves one side of the panel, it appears on the other side. The bat is assigned a left-facing and right-facing set of images (a walking ant), which are cycled through as the bat moves.

Statechart Specification

A statechart for BatSprite's actions appears in Figure 11-7.

The new statechart element in Figure 11-7 is the concurrent state diagram with two concurrent sections: user-based reactions and time-based reactions. Concurrent state diagrams allow the modeling of concurrent activities using this section notation. Concurrent activities are present in all sprites controlled by the user.

The time-based reactions section illustrates the update/draw cycle carried out by the animation loop. The user-based reactions section encapsulates the changes made to the sprite by the user pressing the arrow keys and/or the mouse. A move right transition ...