Killer Game Programming in Java

The Fireball

A fireball starts at the lower righthand side of the panel and travels across to the left. If it hits Jack, the fireball will explode and a corresponding sound will be heard. A fireball that has traveled off the lefthand side of the panel, or has exploded, is reused. The FireBallSprite object is repositioned somewhere on the right edge of the game panel and fired at Jack again.

Only a single fireball is on the screen at a time, so JumpingJack creates only one FireBallSprite object. It is declared in JackPanel's constructor:

    fireball = new FireBallSprite(PWIDTH, PHEIGHT, imsLoader, this, jack);

The fourth argument is a reference to JackPanel allowing the fireball to call its methods; the fifth argument is a reference to the JumperSprite object, jack, allowing the fireball to call its methods.

As the fireball moves left, it keeps checking whether it has hit Jack. If a collision occurs, JackPanel will be asked to display an explosion as FireBallSprite resets its position.

Statechart Specification

The statechart in Figure 12-22 is a useful way of specifying the design needs of FireBallSprite.

Tip

Statecharts were introduced in Chapter 11.

The update/draw cycle driven by JackPanel's animation loop is visible. There are two special cases to consider: when the fireball hits Jack and when it leaves the left side of the panel.

Figure 12-22. The FireBallSprite statechart

The examining environment ...