bouncer.java

书籍"Java_面向事件编程"的附带光盘代码

import objectdraw.*;
import java.awt.Color;

// moves each ball in the array up and down
public class Bouncer extends ActiveObject {
    
    // how many balls to bounce
    private static final int BOUNCES = 20;
    
    // speed and acceleration of ball motion
    private static final double INITSPEED = -3;
    private static final double GRAVITY = .125;
    
    // length of pauses between moving a ball
    private static final int STEPDELAY = 30;
    
    // length of pause between picking balls to bounce
    private static final int BOUNCEDELAY = 250;
    
    // the set of balls to choose from
    BallCollectionInterface allTheBalls;
    
    public Bouncer( BallCollectionInterface theBalls ) {
        allTheBalls = theBalls;
        start();
    }
    
    
    public void run() {
        
        // bounce BOUNCES randomly picked balls.
        for ( int count = 0; count < BOUNCES; count ++ )
            {
                BBall ball = allTheBalls.pickRandomly();
                
                // animate the bounce
                for ( double velocity = INITSPEED;
                      velocity <= -INITSPEED;
                      velocity = velocity + GRAVITY) {
                    ball.move(0,velocity);
                    pause( STEPDELAY);
                }
                
                pause( BOUNCEDELAY);
                
            }
    }
    
}