When i run this code the paintComponent method is not being called It may be very simple error but i dont know why this, plz.

package test;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.image.BufferedImage;
import javax.swing.BorderFactory;
import javax.swing.JPanel;

 class   Userboard extends JPanel 
{
    static BufferedImage image;
    String shape;
    Point start;
    Point end;
    Point mp;
    String selected;
    int ex,ey;//eraser
    int w,h;
    public Userboard() 
    {        

        setOpaque(false);
        System.out.println("paper");
        setBackground(Color.white);

        setBorder(BorderFactory.createLineBorder(Color.black));         
    }
    public  void paintComponent(Graphics g) 
    {
           System.out.println("userboard-paint");
        try
        {

            //g.drawImage(image, 0, 0, this);
            Graphics2D g2 = (Graphics2D)g;
            g2.setPaint(Color.black);
            if(start!=null && end!=null)
            {
                if(selected==("elipse"))
                {
                    System.out.println("userboard-elipse");
                    g2.drawOval(start.x, start.y,(end.x-start.x),(end.y-start.y));
                    System.out.println("userboard-elipse drawn");
                }
                else if(selected==("rect"))
                    g2.drawRect(start.x, start.y, (end.x-start.x),(end.y-start.y));
                else if(selected==("line"))
                    g2.drawLine(start.x,start.y,end.x,end.y);
            }           
        }
            catch(Exception e)
            {}
    }
    //Function to draw the shape on image
    public  void draw()
    {
        System.out.println("Userboard-draw");
        System.out.println(selected);
        System.out.println(start);
        System.out.println(end);
        Graphics2D g2 = image.createGraphics();
        g2.setPaint(Color.black);
        if(start!=null && end!=null)
        {
            if(selected=="line")
                    g2.drawLine(start.x, start.y, end.x, end.y);
            else if(selected=="elipse")
            {
                System.out.println("userboard-elipse");
                g2.drawOval(start.x, start.y, (end.x-start.x),(end.y-start.y));
                System.out.println("userboard-elipse drawn");
            }
            else if(selected=="rect")
                    g2.drawRect(start.x, start.y, (end.x-start.x),(end.y-start.y));
        }
        start=null;
        repaint();
        g2.dispose();
    } 
    //To add the point to the board which is broadcasted by the server  
    public   void addPoint(Point ps,String varname,String shape,String event) 
    {       
        try
        {
            if(end==null)
                end = new Point();
            if(start==null)
                start = new Point();

            if(shape.equals("elipse"))
                this.selected="elipse";
            else if(shape.equals("line"))
                this.selected="line";
            else if(shape.equals("rect"))
                this.selected="rect";
            else if(shape.equals("erase"))
                erase();

            if(end!=null && start!=null)
            {           
                if(varname.equals("end"))
                        end=ps;
                else if(varname.equals("mp"))
                        mp=ps;          
                else if(varname.equals("start"))
                        start=ps;

                if(event.equals("drag"))
                       repaint();
                else if(event.equals("release"))
                        draw();     
            }
              repaint();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
} 
    //Function which provides the erase functionality
    public  void erase() 
    {
        Graphics2D pic=(Graphics2D) image.getGraphics();
        pic.setPaint(Color.white);
        if(start!=null)
        pic.fillRect(start.x, start.y, 10, 10);
    }

    //To set the size of the image

    public void setWidth(int x,int y)
    {
        System.out.println("("+x+","+y+")");
        w=x;
        h=y;
        image = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
    }
    //Function to add buttons into the panel, calling this function returns a panel  

}