如何实现对所有线程程序的控制?

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.geom.*;
import java.util.*;

public class Bounce{
public static void main(String[] args){
JFrame frame = new BounceFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}

class BallRunnable implements Runnable{
public BallRunnable(Ball aBall, Component aComponent){
ball = aBall;
component = aComponent;
}

public void run(){
try{
for(int i = 1; i <= STEPS; i++){
ball.move(component.getBounds());
component.repaint();
Thread.sleep(DELAY);
}
}catch(InterruptedException e){
System.out.println("InterruptedException!");
}
}
private Ball ball;
private Component component;
public static final int STEPS = 1000;
public static final int DELAY = 5;
}
class Ball{
public void move(Rectangle2D bounds){
x += dx;
y += dy;
if (x < bounds.getMinX()){
x = bounds.getMinX();
dx = -dx;
}
if (x + XSIZE >= bounds.getMaxX()){
x = bounds.getMaxX() - XSIZE;
dx = -dx;
}
if (y < bounds.getMinY()){
y = bounds.getMinY();
dy = -dy;
}
if (y + YSIZE >= bounds.getMaxY()){
y = bounds.getMaxY() - YSIZE;
dy = -dy;
}
}
public void speedUp(){
dx++; dy++;
}

public void slowDown(){
dx--; dy--;
}

public Ellipse2D getShape(){
return new Ellipse2D.Double(x, y, XSIZE, YSIZE);
}

private static final int XSIZE = 15;
private static final int YSIZE = 15;
private double x = 0;
private double y = 0;
private double dx = 1;
private double dy = 1;
}

class BallPanel extends JPanel{
public void add(Ball b){
balls.add(b);
}

public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
for (Ball b : balls){
g2.fill(b.getShape());
}
}

private ArrayList<Ball> balls = new ArrayList<Ball>();
}

class BounceFrame extends JFrame{
public BounceFrame(){
setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
setTitle("Bounce");

panel = new BallPanel();
add(panel, BorderLayout.CENTER);
JPanel buttonPanel = new JPanel();
addButton(buttonPanel, "Start",
new ActionListener(){
public void actionPerformed(ActionEvent event){
addBall();
}
});
addButton(buttonPanel, "Exit",
new ActionListener(){
public void actionPerformed(ActionEvent event){
System.exit(0);
}
});
addButton(buttonPanel, "speedUp",
new ActionListener(){
public void actionPerformed(ActionEvent event){
ball.speedUp();
}
});
addButton(buttonPanel, "slowDown",
new ActionListener(){
public void actionPerformed(ActionEvent event){
ball.slowDown();
}
});
add(buttonPanel, BorderLayout.SOUTH);
}

public void addButton(Container c, String title, ActionListener listener){
JButton button = new JButton(title);
c.add(button);
button.addActionListener(listener);
}

public void addBall(){
ball = new Ball();
panel.add(ball);
Runnable r = new BallRunnable(ball, panel);
Thread t = new Thread(r);
t.start();
}
private Ball ball;
private BallPanel panel;
public static final int DEFAULT_WIDTH = 450;
public static final int DEFAULT_HEIGHT = 350;
public static final int STEPS = 1000;
public static final int DELAY = 3;
}
这个是JAVA2核心技术书上一个例子,我自己改了一下,加了一个加速功能一个减速功能,但是只能对一个线程起作用,如何才能同时对所有正在运行的程序发出指令?? 是把所有线程放到一个 线程组里吗? 能不能给个简单点的例子看看?