superpongball.java

书籍"Java_面向事件编程"的附带光盘代码

import objectdraw.*;

// Implements animated balls for variants of Pong with
// multiple obstacles in the playing area
public class SuperPongBall extends ActiveObject {
    
    // Ball's initial speed
    private final static double INITY = 100;
    private static final double XSPEED_RATIO = 1.5;
    
    // Size of ball
    private static final double BALLSIZE = 10;
    
    // delay between moves
    private static final double DELAY= 30;
    
    // the ball itself
    private FilledOval theBall;
    
    // the bricks ball might bounce off
    private RectCollection bricks;
    
    // the boundary within which the ball should stay
    private FramedRect boundary;
    
    // the paddle trying to hit the ball
    private FilledRect paddle;
    
    // current ball speed
    private double xSpeed;
    private double ySpeed = -INITY;
    
    // y coordinate of bottom of screen
    private double offScreen;
    
    // create a new ball.  remember all the things it might hit 
    public SuperPongBall( RectCollection theBricks,
                          FramedRect theBoundary,
                          FilledRect thePaddle,
                          DrawingCanvas theCanvas) {
        
        // set the speed
        RandomDoubleGenerator xGen = 
            new RandomDoubleGenerator( -XSPEED_RATIO*INITY, XSPEED_RATIO*INITY);
        xSpeed = xGen.nextValue();
        
        // draw the ball
        theBall = new FilledOval( thePaddle.getX()+thePaddle.getWidth()/2,
                                  thePaddle.getY() - 2*BALLSIZE,
                                  BALLSIZE, BALLSIZE, theCanvas);
        
        // remember the obstacles
        bricks = theBricks;
        boundary = theBoundary;
        paddle = thePaddle;
        offScreen = theCanvas.getHeight();
        start();
    }
    
    // bounce the ball around the playing area
    public void run(){
        
        double start = System.currentTimeMillis();
        
        while ( theBall.getY() < offScreen ) {
            
            pause(DELAY);
            
            double elapsedTime = System.currentTimeMillis() - start;
            start = start + elapsedTime;
            
            theBall.move( elapsedTime*xSpeed/1000, elapsedTime*ySpeed/1000);
            
            // see if you need to bounce off one of the boundary's sides
            if ( theBall.getX() < boundary.getX() ) {
                xSpeed = -xSpeed;
                theBall.move( 2* (boundary.getX()- theBall.getX()),0 );
            } else if ( theBall.getX() > boundary.getX() +boundary.getWidth() - BALLSIZE) {
                xSpeed = -xSpeed;
                theBall.move( 2*(boundary.getX() + boundary.getWidth() - BALLSIZE - theBall.getX()),0);
            }
            
            // see if you hit the top of the boundary
            if ( theBall.getY() < boundary.getY() ) {
                ySpeed = -ySpeed;
                theBall.move(0, 2*(boundary.getY()-theBall.getY()));
            }
            
            // see if you hit a brick
            FilledRect hitBrick = bricks.findFirstOverlap(theBall);
            if ( hitBrick != null){
                bounceOffRect( hitBrick);
            }
            
            // check the paddle
            if ( theBall.overlaps(paddle) ) {
                bounceOffRect(paddle);
            }
        }
        
    }
    
    // the following implements a crude approximation of the phsyical process
    // of a ball bouncing off a brick (or the paddle).  Anomalies will occur!
    private void bounceOffRect(FilledRect box){
        double centerX = theBall.getX()+BALLSIZE/2;
        double centerY = theBall.getY()+BALLSIZE/2;
        
        if ( centerX > box.getX() && centerX < box.getX()+box.getWidth()){
            if (ySpeed > 0) {
                theBall.move( 0, 2*(box.getY() - (theBall.getY() + theBall.getHeight())));
            } else {
                theBall.move( 0, 2*(box.getY()+box.getHeight() - theBall.getY() ));
            }
            ySpeed = -ySpeed;
        } else if (centerY > box.getY() && centerY < box.getY()+box.getHeight()) {
            if (xSpeed > 0) {
                theBall.move( 2*(box.getX() - (theBall.getX() + theBall.getWidth())), 0);
            } else {
                theBall.move( 2*(box.getX()+box.getWidth() - theBall.getX() ), 0);
            }
            xSpeed = -xSpeed;
            
        }
    }
}