Using paint() for a JPanel in a ScrollBar

Question

i have a class that extends JPanel and paints some graphics in it using the function paint(). like g.drawString.. i had to add an instantition of that class in the container of my main class within a scrollbar. It initially painted well but when i scroll, it gets distorted. its something like this
public class PaintedPane extends JPanel
public PaintedPane()
paint()
other codes here..
public class MainClass extends JFrame
public PaintedPane pane;
public JScrollbar scroll;
public MainClass()
pane = new PaintedPane();
scroll = new JScrollBar(pane);
it seems that the pane wont update the part of the pane not initially exposed because of the scrollBar. how can i fix it? thanks!

Answer 1

sorry for the wrong section.
here is the code:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class MainClass extends JFrame
     public TextDraw td;
     public JScrollPane pane;
     public Container c;
     public MainClass()
          c = getContentPane();
          c.setLayout(new FlowLayout());
          td = new TextDraw();
          td.setPreferredSize(new Dimension(300, 300));
          pane = new JScrollPane(td);
          pane.setPreferredSize(new Dimension(300, 200));
          c.add(pane);
          setSize(400, 400);
          show();
     public static void main(String args[])
          MainClass m = new MainClass();
          m.addWindowListener(
               new WindowAdapter()
                    public void windClosing(WindowEvent e)
                         System.exit(0);
}and another java file for the TextDraw
import javax.swing.*;
import java.awt.*;
public class TextDraw extends JPanel
   public TextDraw()
         setBackground(Color.WHITE);           
            setSize(500,  500);
            show();
   public void paint(Graphics g)
          for(int x = 0; x < 20; x++)
               g.drawString("Hello world!", 20, (x)*20);
               g.fillRect(5, (x)*20, 10, 10);
}i dont realy know what to do to fix this. And if i chang the values of the "setSize(400, 400)" of the MainClass to "setSize(300, 300)" it works fine. why is it like that? sorry im not very familiar with all the paint, paintComponent and graphics things. thanks!