Chapter 9 Active Objects+ Boxball Project Design

• Animations!

• What are they?– Snapshots of objects in different positions– When viewed quickly appear to be moving

A Virtual Flipbook:

Animating an Object

• First create an object

• Then– Move it a little– Pause for the user to see it– Repeat

FallingBallpublic 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();

}}

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

Using Active Objectspublic 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 );

}

}

What if…

• We wanted the falling object to look like a raindrop

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 );

A Controller Classpublic 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 );

}}

A Falling Raindroppublic 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();

}}

Active Object Interactions

• Accomplished with methods and parameters

• A RainCloud:– RainCloud continuously generates drops– Drops fall and disappear at the bottom

The RainCloud Classpublic 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++;

}}

}

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

A New Kind of Raindrop

1. Created at the top of the screen

2. Falls to the bottom

3. Raises the waterline

Falling Dropletpublic 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 );

}}

}

Boxball

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

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

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

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

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

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