ExampleA.java

public class BouncingBalls extends GraphicsApp {

    private static final int CANVAS_WIDTH = 1280;
    private static final int CANVAS_HEIGHT = 360;
    private static final Color BACKGROUND_COLOR = Colors.WHITE;

    private static final int DEFAULT_SPEED = 5;
    private static final int MIN_SPEED = 1;
    private static final int BALL_RADIUS = 25;
    private static final Color BALL_COLOR = Colors.RED;

    private Circle ball;
    private boolean currentlyMovingToRight = true;
    private int currentSpeed = DEFAULT_SPEED;

    @Override
    public void initialize() {
        setCanvasSize(CANVAS_WIDTH, CANVAS_HEIGHT);
        // Erstellen des Balls am Mittelpunkt der Zeichenfläche
        ball = new Circle(CANVAS_WIDTH / 2, CANVAS_HEIGHT / 2, BALL_RADIUS, BALL_COLOR);
    }

    @Override
    public void draw() {
        drawBackground(BACKGROUND_COLOR);
        updateBall();
        drawBall();
    }

    private void updateBall() {
        // Umkehr der Bewegungsrichtung, falls der Ball den Bildschirmrand im letzten Frame verlassen hat
        if (hasLeftScreen(ball)) {
            currentlyMovingToRight = !currentlyMovingToRight;
        }
        int speed = currentlyMovingToRight ? currentSpeed : -currentSpeed;
        ball.move(speed, 0);
    }

    // Prüft ob das übergebene Circle-Objekt den rechten oder linken Bildschirmrand verlassen hat
    private boolean hasLeftScreen(Circle ball) {
        if ((ball.getXPos() - ball.getRadius()) >= CANVAS_WIDTH) {
            return true;
        }
        if ((ball.getXPos() + ball.getRadius()) <= 0) {
            return true;
        }
        return false;
    }

    private void drawBall() {
        ball.draw();
    }

    @Override
    public void onKeyPressed(KeyPressedEvent event) {
        super.onKeyPressed(event);
        switch (event.getKeyCode()) {
            case KeyPressedEvent.VK_UP:
                increaseSpeed();
                break;
            case KeyPressedEvent.VK_DOWN:
                decreaseSpeed();
                break;
            default:
                break;
        }
    }

    private void increaseSpeed() {
        currentSpeed++;
    }

    private void decreaseSpeed() {
        currentSpeed--;
        if (currentSpeed < MIN_SPEED) {
            currentSpeed = MIN_SPEED;
        }
    }

    public static void main(String[] args) {
        GraphicsAppLauncher.launch();
    }
}