1. The Bouncing Ball Problem (Independent Threads)

2. Contents Problem Description A Single-Threading Solution
A Multithreading Solution
New Requirement: Bouncing an Image

3. I. Problem Description
Develop a GUI program that animates a bouncing ball by continually moving the ball 1,000 times, each time 1 pixel in both x and y directions
As soon as you click the Start button, the program launches a new ball from the upper- left corner of the screen and the ball begins bouncing (see the next slide)
The delay between two moves is 3 ms

5. II. A Single-Threading Solution
The Main Class
Developing the View
Adding Listeners to the Buttons
The Shortcoming of This Solution

6. 1. The Main Class

7. 2. Developing the View

8. 2.1. Add ballPanel to CENTER

9. 2.2. Add buttonPanel to SOUTH

10. 3. Adding Listeners to the Buttons
3.1. Adding Listener to the Close Button
3.2. Adding Listener to the Start Button

11. 3.1. Adding Listener to the Close Button

12. 3.2. Adding Listener to the Start Button
Bouncing a Ball
Taking Care of Multiple Balls

13. Bouncing a Ball

14. Make BallPanel as a Separate Class

15. Develop the Ball Class

18. Refactor the Position & Gradient Classes

19. Develop bounceBall()

21. Move the Ball

24. Sleep for 3 ms

25. Fit the Ball to the Panel

29. 3.2.3. Bouncing Multiple Balls

30. 4. The Shortcoming of This Solution
The bouncing of a ball completely takes over the application
We cannot interact with the program until the ball has finished bouncing

31. III. A Mutithreading Solution
A simple procedure for running a task in a separate thread:
Place the code for the task into the run method of a class that implements the Runnable interface public interface Runnable { void run(); } … class MyRunnable implements Runnable { public void run() { task code } }

32. Construct an object of your class: Runnable r = new MyRunnable();
Construct a Thread object from the Runnable: Thread t = new Thread(r);
Start the thread: t.start();

33. III. A Mutithreading Solution
Run the bouncing code in a separate thread

34. Execute the application and click Start button many times to get ConcurrentModificationException

35. Replace paint() by repaint()

36. Let the Balls Run Forever

37. IV. New Requirement: Bouncing an Image

38. Solution
Look for the place where we can replace the ball by the image

39. Modify the listener of the Start Button

40. Modify bounceBall() by introducing an inheritance structure
The main difference between BlackBall and ImageBall is show()

42. Execute the application to make sure that BlackBall works

44. Reference
Core Java, Volume I – Fundamentals, Eighth Edition, Chapter 14. Cay S. Horstmann and Gary Cornell. Prentice Hall, 2008