How to stop the flickering of the background image of the applet?

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Java

applet

So I added a background Image to an applet and now whenever I try to run
the Applet the background image starts to flicker, I have added more
images and button on top of the background is that causing the flickers
or is there something wrong with my code?

import java.applet.Applet;
    import java.awt.event.*;
    import java.awt.*;
    import java.awt.Color;

    //<applet code="game" width="500" height="500">

    public class game extends Applet implements Runnable {  //interface for thread

    	int x = 350, y = 10,z=10,n=0;
    	Image bal,a,bg;
    	Boolean flag=true,arr=false;
    	Button b;
    	String str="SCORE : ";
    	Label l;
    	public void start() {
        try 
        { 
            MediaTracker tracker = new MediaTracker (this);
            bg= getImage(getDocumentBase(),"bg.jpg"); //setting background
            tracker.addImage(bg, 0);
        } catch (Exception e) {}
        bg= getImage(getDocumentBase(),"bg.jpg");   //get background
        bal=getImage(getDocumentBase(),"balloon.png");  //get balloon
        a=getImage(getDocumentBase(),"arrow.png"); //get arrow
        new Thread(this).start();
        b=new Button("SHOOT");
        add(b);
        b.addActionListener(new ActionListener(){ //perform this when clicked
        public void actionPerformed(ActionEvent e)
        {
	    arr=true;
        }});
        setSize(500, 500);
        setBackground(Color.white);   
        }
        public void run() {
        while (true) {
           if(arr)
          {
           updates();
          }
           update();
           try {
                Thread.sleep(25);           //making thread sleep
            } catch (InterruptedException ex) {}
            if(z>300)
           {
           	arr=false;
            z=10;
            }
            if(z+70>=x && (y>=200 && y<=300))
                 {
                 	n=n+10;
                    showStatus("HIT!");
      	public void updates(){           //increments the arrow
      	z+=25;
      	repaint();
      	}
      	public void update() {          //increments the balloon
        if(flag)
       		{ y += 6; }
        else
       		{ y -= 6; }                  //decrements the balloon
        if(y>450) flag=false;
        if(y<10) flag=true;
        repaint();
      	}

      	public void paint(Graphics g) {
        	g.drawImage(bg,0,0,500,500,this);
        	g.drawImage(bal,x, y, 75, 75,this);
        	g.drawImage(a,z+10,250,70,50,this);
        	g.drawString(str+n,220,480);
      	}}

What I have tried:

I have no idea what is causing this..