P.18 (Change Once Only: boolean isDown)
// This method is called whenever
public void act() {
// if( not is Down and "g" is down )
if( !isDown && Greenfoot.isKeyDown ("g") ) {
setImage ("white-key-down.png");
isDown = true;
}
// if( isDown and "g" is not down )
if( isDown && !Greenfoot.isKeyDown ("g") ) {
setImage ("white-key.png");
isDown = false;
}
}