Moving Ball Using Thread in Java Example

import java.awt.*; 
 import java.awt.event.*; 
 import java.applet.*; 
 /*<applet code="MovingBalls" width=500 height=250> </applet>*/ 
 public class MovingBalls extends Applet implements ActionListener,Runnable 
 { 
         int d=100; 
         Thread t; 
         Button btnStart,btnStop,btnPause,btnResume; 
         int i,m,j; 
         TextField txtSpeed; 
         Label lblSpeed; 
         public void init() 
            { 
                lblSpeed=new Label("Enter speed in ms"); 
                txtSpeed=new TextField(5); 
                btnStart=new Button("Start"); 
                btnStop=new Button("Stop"); 
                btnPause=new Button("Pause"); 
                btnResume=new Button("Resume"); 
                btnStart.addActionListener(this); 
                btnStop.addActionListener(this); 
                btnPause.addActionListener(this); 
                btnResume.addActionListener(this); 
                add(lblSpeed); 
                add(txtSpeed); 
                add(btnStart); 
                add(btnStop); 
                add(btnPause); 
                add(btnResume); 
            } 
               public void actionPerformed(ActionEvent ae) 
                 { 
                      if((ae.getSource()==btnStart)&&(t==null)) 
                       { 
                            t = new Thread(this); 
                            t.start(); 
                        } 
                       else if((ae.getSource()==btnStop)&&(t != null)) 
                        { 
                            t.stop(); 
                            t=null; 
                        } 
                      else if((ae.getSource()==btnPause)&&(t != null)) 
                        { 
                           t.suspend(); 
                        } 
                     else if((ae.getSource()==btnResume)&&(t != null)) 
                        { 
                             t.resume(); 
                         } 
                  } 
                      public void run() 
                        { 
                            m=((int)(Math.random()*1000))%700; 
                            for(j=500;;j--) 
                                { 
                                   if(j<-1000) 
                                     { 
                                        m=((int)(Math.random()*1000))%700; 
                                         j=500; 
                                     } 
                                   repaint(); 
                                   try 
                                     { 
                                         Thread.sleep(Integer.parseInt(txtSpeed.getText())); 
                                     } 
                                         catch(Exception e){} 
                                 } 
                          } 
              public void paint(Graphics g) 
           { 
                 for(int k=0,i=d;i>0;i--,k++) 
                       { 
                            g.setColor(new Color(100+k,100,100+k)); 
                            g.drawOval((m+200)%700+k/2,k/2+j,i,i); 
                        } 
                           for(int k=0,i=d;i>0;i--,k++) 
                              { 
                                    g.setColor(new Color(100+k,200,80+k)); 
                                    g.drawOval(k/2+(m%700),k/2+j,i,i); 
                               } 
                          for(int k=0,i=d;i>0;i--,k++) 
                             { 
                                    g.setColor(new Color(10+k,40,90+k)); 
                                    g.drawOval(k/2+(m+500)%700,k/2+j,i,i); 
                             } 
              } 
 }