1. Chapter 9 Active Objects + Boxball Project Design Animations! What are they? –Snapshots of objects i n different positions –When viewed quickly appear to be moving

2. A Virtual Flipbook:

3. Animating an Object First create an object Then –Move it a little –Pause for the user to see it –Repeat

4. FallingBall public class FallingBall extends ActiveObject { public FallingBall( Location initialLocation, DrawingCanvas aCanvas ){ canvas = aCanvas; ballGraphic = new FilledOval (initialLocation, SIZE, SIZE, canvas ); start(); } public void run() { while ( ballGraphic.getY() < canvas.getHeight() ) { ballGraphic.move( 0, Y_STEP ); pause( DELAY_TIME ); } ballGraphic.removeFromCanvas(); }

5. Defining an Active Object define a class that extends ActiveObject ensure the class includes a run method pause occasionally within the run method include start(); usually as the last statement in the constructor

6. Using Active Objects public class FallingBallController extends WindowController { private FallingBall droppedBall; public void begin() { new Text("Click to make a falling ball…”, INSTR_LOCATION, canvas ); } public void on MouseClick( Location point ) { droppedBall = new FallingBall( point, canvas ); }

7. What if… We wanted the falling object to look like a raindrop

8. Image and VisibleImage Classes In the controller class: private Image rainPicture; rainPicture = getImage("raindrop.gif" ); Can be used anywhere: new VisibleImage( rainPicture, 0, canvas.getWidth()/2, canvas );

9. A Controller Class public class FallingRainPicController extends WindowController { private Image rainPicture; public void begin() { new Text("Click to make a falling raindrop…", INSTR_LOCATION, canvas ); rainPicture = getImage( "raindrop.gif" ); } public void onMouseClick( Location point ) { new FallingRainDrop( rainPicture, point, canvas ); }

10. A Falling Raindrop public class FallingRainDrop extends ActiveObject { private static final int DELAY_TIME = 33; private static final double Y_SPEED=4; private VisibleImage ballGraphic; private DrawingCanvas canvas; public FallingRainDrop( Image rainPic, Location initialLocation, DrawingCanvas aCanvas ) { canvas = aCanvas; rainGraphic = new VisibleImage( rainPic, initialLocation, canvas ); start(); } public void run() { while ( rainGraphic.getY() < canvas.getHeight() ) { rainGraphic.move( 0, Y_SPEED ); pause ( DELAY_TIME ); } rainGraphic.removeFromCanvas(); }

11. Active Object Interactions Accomplished with methods and parameters A RainCloud: –RainCloud continuously generates drops –Drops fall and disappear at the bottom

12. The RainCloud Class public class RainCloud extends ActiveObject { public RainCloud( DrawingCanvas aCanvas, Image aRainPic) { rainPic = aRainPic; canvas = aCanvas; start(); } public void run() { RandomIntGenerator xGenerator = new RandomIntGenerator( 0, canvas.getWidth() ); int dropCount = 0; while ( dropCount < MAX_DROPS ) { new FallingRainDrop( rainPic, new Location( xGenerator.nextValue(), 0 ), canvas); pause( DELAY_TIME ); dropCount++; }

13. Interactions Between Active and Non-Active Objects An Active Object: –Droplet in the shape of an oval Created at the top of canvas, falls to the bottom A Non-Active Object: –Waterline in the shape of a FilledRect Rises as drops fall

14. A New Kind of Raindrop 1.Created at the top of the screen 2.Falls to the bottom 3.Raises the waterline

15. Falling Droplet public class FallingDroplet extends ActiveObject { private FilledOval dropletGraphic; private FilledRect collector; public FallingDroplet( Location initialLocation, DrawingCanvas canvas, FilledRect aCollector ) { dropletGraphic = new FilledOval( initialLocation, SIZE, SIZE, canvas ); collector = aCollector; start(); } public void run() { while ( dropletGraphic.getY() < collector.getY() ) { dropletGraphic.move( 0, Y_STEP ); pause( DELAY_TIME ); } dropletGraphic.removeFromCanvas(); if ( collector.getY() > 0 ) { collector.setHeight( collector.getHeight() + SIZE/4 ); collector.move( 0, -SIZE/4 ); }

16. Boxball

17. Classes break problem up Boxball Class: –sets up arena, title, status message "Let's Play" –sets up bar and easy/med/hard buttons –sets up target box –onMouseClick if on easy/med/hard button, moves bar to different level if clickPoint is above bar creates a new Ball

18. Boxball design, continued Box Class: –manages the FilledRect that is the target –methods to Construct a Box moveBox move to different x-position setSize change the size of the box getLeft retrieve the x position of left side of box getRight retrieve the x position of right side

19. Box Class examples target = new Box(100, 50, canvas); –creates a new Box at x position 100, width 50 target.setSize(35); –changes width of box to 35 target.setSize(BALL_SIZE*1.5); –width set to 50% larger than ball target.moveBox(); –moves box to a random x position

20. Boxball Design, continued Ball Class –constructor to create a new Ball remember the canvas in instance variable –run method to animate ball so it drops while ball is above the bottom of the arena, –advance ball by 10 pixels or so –pause 50 milliseconds or so after the ball reaches bottom, check if it is within left and right sides of box

21. Ball class constructor examples Part 3 – new Ball(BALL_SIZE, point, canvas); ball will be created at point and fall. Part 4 –new Ball(BALL_SIZE, point, target, canvas); ball will also be able to access target to check if within left and right edges Another possibility— –new Ball(BALL_SIZE, point, arena, target, canvas); ball will also be able to access arena to tell when to stop –each new variation has to add actual parameters

22. Have fun with challenges Check with instructor frequently to stay on track Email code over weekend for help This is a crucial component to master Reading textbook can help with concepts