EVENT-DRIVEN PROGRAMMING AND ANIMATIONS - Introduction to Java Programming: Comprehensive Version - page 618

19
20 // Create an animation for moving the ball
21 animation = new Timeline(
22

create animation

new KeyFrame(Duration.millis( 50 ), e -> moveBall()));

23 animation.setCycleCount(Timeline.INDEFINITE); keep animation running

start animation 24 animation.play(); // Start animation

25 }
26
27 public void play() {
28 animation.play();
29 }
30
31 public void pause() {
32 animation.pause();
33 }
34
35

play animation

pause animation

public void increaseSpeed() {

36 animation.setRate(animation.getRate() + 0.1 );

increase animation rate

37 }
38
39 public void decreaseSpeed() {
40 animation.setRate(
41 animation.getRate() > 0 ? animation.getRate() - 0.1 : 0 );
42 }
43
44

decrease animation rate

public DoubleProperty rateProperty() {

45 return animation.rateProperty();

46 }
47
48 protected void moveBall() {

49 // Check boundaries

50 if (x < radius || x > getWidth() - radius) {

51 dx *= -1 ; // Change ball move direction

change horizontal direction

52 }
53 if (y < radius || y > getHeight() - radius) {

54 dy *= -1 ; // Change ball move direction change verticaal direction

55 }
56
57 // Adjust ball position
58 x += dx;
59 y += dy;
60 circle.setCenterX(x);
61 circle.setCenterY(y);
62 }
63 }

set new ball position

BallPane extends Pane to display a moving ball (line 9). An instance of Timeline is
created to control animation (lines 21 and 22). This instance contains a KeyFrame object that
invokes the moveBall() method at a fixed rate. The moveBall() method moves the ball to
simulate animation. The center of the ball is at ( x , y ), which changes to ( x + dx , y + dy ) on
the next move (lines 58-61). When the ball is out of the horizontal boundary, the sign of dx is
changed (from positive to negative or vice versa) (lines 50-52). This causes the ball to change
its horizontal movement direction. When the ball is out of the vertical boundary, the sign of dy
is changed (from positive to negative or vice versa) (lines 53-55). This causes the ball to change
its vertical movement direction. The pause and play methods (lines 27-33) can be used to
pause and resume the animation. The increaseSpeed() and decreaseSpeed() methods
(lines 35-42) can be used to increase and decrease animation speed. The rateProperty()