Help me to Edit this program

Question

Hi All,
Can anyone kind enought to help me to add the START and STOP button for this "bouncing ball" program that i got from the internet ? Below is the java coding.
import java.awt.*;
import java.applet.*;
class Obstacle
     public Rectangle r;
     Graphics g;
     public Obstacle(int x,int y,int w,int h)
          r=new Rectangle(x,y,w,h);
     public void paint(Graphics gr)
          g=gr;
          g.setColor(Color.lightGray);
          g.draw3DRect(r.x,r.y,r.width,r.height,true);
class CollideBall
     int width, height;
     public static final int diameter=20;
     //coordinates and value of increment
     double x, y, xinc, yinc, coll_x, coll_y;
     boolean collide;
     Color color;
     Graphics g;
     Rectangle r;
     //the constructor
     public CollideBall(int w, int h, int x, int y, double xinc, double yinc, Color c)
          width=w;
          height=h;
          this.x=x;
          this.y=y;
          this.xinc=xinc;
          this.yinc=yinc;          
          color=c;          
          r=new Rectangle(150,80,130,90);
     public double getCenterX() {return x+diameter/2;}
     public double getCenterY() {return y+diameter/2;}
     public void alterRect(int x, int y, int w, int h)
          r.move(x,y);
          r.resize(w,h);
     public void move()
          if (collide)
               double xvect=coll_x-getCenterX();
               double yvect=coll_y-getCenterY();
               if((xinc>0 && xvect>0) || (xinc<0 && xvect<0))
                    xinc=-xinc;
               if((yinc>0 && yvect>0) || (yinc<0 && yvect<0))
                    yinc=-yinc;
               collide=false;
          x+=xinc;
     y+=yinc;
          //when the ball bumps against a boundary, it bounces off
     if(x<6 || x>width-diameter)
          xinc=-xinc;
               x+=xinc;
          if(y<6 || y>height-diameter)
          yinc=-yinc;
               y+=yinc;
          //cast ball coordinates to integers
          int x=(int)this.x;
          int y=(int)this.y;
          //bounce off the obstacle
          //left border
          if(x>r.x-diameter&&x<r.x-diameter+7&&xinc>0&&y>r.y-diameter&&y<r.y+r.height)
          xinc=-xinc;
               x+=xinc;
          //right border
          if(x<r.x+r.width&&x>r.x+r.width-7&&xinc<0&&y>r.y-diameter&&y<r.y+r.height)
          xinc=-xinc;
               x+=xinc;
          //upper border
          if(y>r.y-diameter&&y<r.y-diameter+7&&yinc>0&&x>r.x-diameter&&x<r.x+r.width)
               yinc=-yinc;
               y+=yinc;
          //bottom border
          if(y<r.y+r.height&&y>r.y+r.height-7&&yinc<0&&x>r.x-diameter&&x<r.x+r.width)
               yinc=-yinc;
               y+=yinc;
     public void hit(CollideBall b)
          if(!collide)
               coll_x=b.getCenterX();
               coll_y=b.getCenterY();
               collide=true;
     public void paint(Graphics gr)
          g=gr;
          g.setColor(color);
          //the coordinates in fillOval have to be int, so we cast
          //explicitly from double to int
          g.fillOval((int)x,(int)y,diameter,diameter);
          g.setColor(Color.white);
          g.drawArc((int)x,(int)y,diameter,diameter,45,180);
          g.setColor(Color.darkGray);
          g.drawArc((int)x,(int)y,diameter,diameter,225,180);
public class BouncingBalls extends Applet implements Runnable
     Thread runner;     
     Image Buffer;
Graphics gBuffer;          
CollideBall ball[];
     Obstacle o;
//how many balls?
static final int MAX=10;
     boolean intro=true,drag,shiftW,shiftN,shiftE,shiftS;
     boolean shiftNW,shiftSW,shiftNE,shiftSE;
     int xtemp,ytemp,startx,starty;
     int west, north, east, south;
     public void init()
          Buffer=createImage(size().width,size().height);
          gBuffer=Buffer.getGraphics();                         
          ball=new CollideBall[MAX];
          int w=size().width-5;
          int h=size().height-5;          
          //our balls have different start coordinates, increment values
          //(speed, direction) and colors
          ball[0]=new CollideBall(w,h,50,20,1.5,2.0,Color.orange);
ball[1]=new CollideBall(w,h,60,210,2.0,-3.0,Color.red);
ball[2]=new CollideBall(w,h,15,70,-2.0,-2.5,Color.pink);
ball[3]=new CollideBall(w,h,150,30,-2.7,-2.0,Color.cyan);
ball[4]=new CollideBall(w,h,210,30,2.2,-3.5,Color.magenta);
          ball[5]=new CollideBall(w,h,360,170,2.2,-1.5,Color.yellow);
          ball[6]=new CollideBall(w,h,210,180,-1.2,-2.5,Color.blue);
          ball[7]=new CollideBall(w,h,330,30,-2.2,-1.8,Color.green);
          ball[8]=new CollideBall(w,h,180,220,-2.2,-1.8,Color.black);
          ball[9]=new CollideBall(w,h,330,130,-2.2,-1.8,Color.gray);
          o=new Obstacle(150,80,130,90);
          west=o.r.x;
          north=o.r.y;
          east=o.r.x+o.r.width;
          south=o.r.y+o.r.height;
     public void start()
          if (runner == null)
               runner = new Thread (this);
               runner.start();
public void stop()
          if (runner != null)
     runner.stop();
     runner = null;
     public void run()
          while(true)
               Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
               try {runner.sleep(15);}
     catch (Exception e) { }               
               //move our balls around
               for(int i=0;i<MAX;i++)
                    ball.move();
               handleCollision();
               repaint();     
     boolean collide(CollideBall b1, CollideBall b2)
          double wx=b1.getCenterX()-b2.getCenterX();
          double wy=b1.getCenterY()-b2.getCenterY();
          //we calculate the distance between the centers two
          //colliding balls (theorem of Pythagoras)
          double distance=Math.sqrt(wx*wx+wy*wy);
          if(distance<b1.diameter)                         
               return true;          
               return false;     
     void changeCursor(int x, int y)
          Rectangle r=new Rectangle(o.r.x+1,o.r.y+1,o.r.width-1,o.r.height-1);
          Frame BrowserFrame;
          Component ParentComponent;
          ParentComponent = getParent();
          while ( ParentComponent != null &&
          !(ParentComponent instanceof Frame))           
          ParentComponent = ParentComponent.getParent();          
          BrowserFrame = (Frame) ParentComponent;
          if(shiftNW||shiftSE)
               BrowserFrame.setCursor(Frame.SE_RESIZE_CURSOR);
          else if(shiftNE||shiftSW)
               BrowserFrame.setCursor(Frame.SW_RESIZE_CURSOR);
          else if(shiftW)
               BrowserFrame.setCursor(Frame.W_RESIZE_CURSOR);
          else if(shiftN)
               BrowserFrame.setCursor(Frame.N_RESIZE_CURSOR);
          else if(shiftE)
               BrowserFrame.setCursor(Frame.W_RESIZE_CURSOR);
          else if(shiftS)
               BrowserFrame.setCursor(Frame.N_RESIZE_CURSOR);
          else if(r.inside(x,y))
               BrowserFrame.setCursor(Frame.MOVE_CURSOR);
          else
               BrowserFrame.setCursor(Frame.DEFAULT_CURSOR);
     public boolean mouseMove(Event evt,int x,int y)
          //the corner areas of the obstacle
          Rectangle nw,sw,ne,se;
          nw=new Rectangle(o.r.x-2,o.r.y-2,4,4);
          if(nw.inside(x,y))
               shiftNW=true;
          else shiftNW=false;
          sw=new Rectangle(o.r.x-2,o.r.y+o.r.height-2,4,4);
          if(sw.inside(x,y))
               shiftSW=true;
          else shiftSW=false;
          ne=new Rectangle(o.r.x+o.r.width-2,o.r.y-2,4,4);
          if(ne.inside(x,y))
               shiftNE=true;
          else shiftNE=false;
          se=new Rectangle(o.r.x+o.r.width-2,o.r.y+o.r.height-2,4,4);
          if(se.inside(x,y))
               shiftSE=true;
          else shiftSE=false;          
          if(x>o.r.x-2&&x<o.r.x+2&&y>o.r.y&&y<o.r.y+o.r.height)
               shiftW=true;
          else shiftW=false;
          if(x>o.r.x+o.r.width-2&&x<o.r.x+o.r.width+2
               &&y>o.r.y&&y<o.r.y+o.r.height)
               shiftE=true;
          else shiftE=false;
          if(y<o.r.y+2&&y>o.r.y-2&&x>o.r.x&&x<o.r.x+o.r.width)
               shiftN=true;
          else shiftN=false;
          if(y>o.r.y+o.r.height-2&&y<o.r.y+o.r.height+2
               &&x<o.r.x+o.r.width)
               shiftS=true;
          else shiftS=false;
          changeCursor(x,y);
          return true;
     public boolean mouseDown(Event evt,int x,int y)
          Rectangle r=new Rectangle(o.r.x+2,o.r.y+2,o.r.width-4,o.r.height-4);
          if(r.inside(x,y))
               drag=true;
               startx=x;
               starty=y;
               xtemp=o.r.x;
               ytemp=o.r.y;
          else drag=false;
          changeCursor(x,y);
          return true;
     public boolean mouseDrag(Event evt,int x,int y)
          intro=false;
          Rectangle bounds=new Rectangle(5,5,size().width-5,size().height-5);
          int endx, endy;          
          endx=x-startx;
          endy=y-starty;     
          //disable mouse actions past boundaries
          if(x<5)x=5;
          if(y<5)y=5;
          if(x>bounds.width)x=bounds.width;
          if(y>bounds.height)y=bounds.height;
          if(drag)
               //disallow to move past border
               int ox=endx+xtemp;
               int oy=endy+ytemp;
               if(ox<5)ox=5;
               if(oy<5)oy=5;
               if(ox>bounds.width-o.r.width)
                    ox=bounds.width-o.r.width;
               if(oy>bounds.height-o.r.height)
                    oy=bounds.height-o.r.height;     
               o.r.move(ox,oy);                    
               west=o.r.x;
               north=o.r.y;
               east=o.r.x+o.r.width;
               south=o.r.y+o.r.height;                              
          else
               if(shiftNW){west=x;north=y;}
               else if(shiftNE){east=x;north=y;}
               else if(shiftSW){west=x;south=y;}
               else if(shiftSE){east=x;south=y;}
               else if(shiftW)west=x;
               else if(shiftE)east=x;
               else if(shiftN)north=y;
               else if(shiftS)south=y;                                                       
               //disallow resizing below 40*40
               int MIN=40;
               if(east-west<MIN)
                    //shiftNW=shiftNE=shiftSW=shiftSE=shiftW=shiftE=false;
                    if(shiftW||shiftNW||shiftSW)
                         west=east-MIN;
                    if(shiftE||shiftNE||shiftSE)
                         east=west+MIN;
               if(south-north<MIN)
                    //shiftNW=shiftNE=shiftSW=shiftSE=shiftN=shiftS=false;
                    if(shiftN||shiftNW||shiftNE)
                         north=south-MIN;
                    if(shiftS||shiftSE||shiftSW)
                         south=north+MIN;
          //report altering of obstacle to ball objects and obstacle
          for(int i=0;i<MAX;i++)
               ball[i].alterRect(o.r.x,o.r.y,o.r.width,o.r.height);
          o.r.move(west,north);
          o.r.resize(east-west, south-north);
          changeCursor(x,y);
          return true;
     private void handleCollision()
          //we iterate through all the balls, checking for collision
          for(int i=0;i<MAX;i++)
               for(int j=0;j<MAX;j++)
                         if(i!=j)
                              if(collide(ball[i], ball[j]))
                                   ball[i].hit(ball[j]);
                                   ball[j].hit(ball[i]);
     public void update(Graphics g)
          paint(g);
     public void paint(Graphics g)
          gBuffer.setColor(Color.lightGray);
          gBuffer.fillRect(0,0,size().width,size().height);
          gBuffer.draw3DRect(5,5,size().width-10,size().height-10,false);               
          //paint the obstacle rectangle
          o.paint(gBuffer);
          //paint our balls
          for(int i=0;i<MAX;i++)
                    ball[i].paint(gBuffer);     
          if(intro)
               gBuffer.setColor(Color.red);
               gBuffer.setFont(new Font("Helvetica", Font.PLAIN, 12));               
               gBuffer.drawString("You can move and resize the rectangle!",20,30);
               gBuffer.setFont(new Font("Helvetica", Font.PLAIN, 10));
          g.drawImage (Buffer,0,0, this);                    

Answer 1

Hello, please use code tags next time you post code. You can do so by adding [code] [/code] round blocks of code. So
[code]
class Code {
private static final String codeHere = "code here";
[/code]
will be rendered as
class Code {
  private static final String codeHere = "code here";
We will not do your homework for you, we will however help when you are stuck and point you in the right direction. So what have you tried? What happened?
Don't know how to begin? What makes the ball move?