Lines disappearing from the frame when minimizing the window

Question

I drew some lines on a frame but when I minimize the window , the lines disappear. I dont know why. Please help me. My code is as follows: (Sorry...I dont know how to tag the code to make it more readable)
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.geom.*;
public class Pos extends Container {
public static void main(String args[]) {
Pos p = new Pos();
     p.getPosition();
JButton bn = new JButton("Draw Line");
int posx=0;
int posy=0;
int i=0;
int x[] = new int[4];
int y[] = new int[4];
public void getPosition() {
final JFrame frame = new JFrame("Mouse Position");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel label = new JLabel();
label.setHorizontalAlignment(JLabel.CENTER);
          MouseListener mouseListener = new MouseListener(){
               public void mouseEntered(MouseEvent evnt){
               public void mouseExited(MouseEvent evnt){
               public void mousePressed(MouseEvent evnt){
               public void mouseReleased(MouseEvent evnt){
               public void mouseClicked(MouseEvent evnt) {
                    showMousePos(evnt);
               private void showMousePos(MouseEvent evnt) {
JLabel src = (JLabel)evnt.getComponent();
               posx = MouseInfo.getPointerInfo().getLocation().x;
               posy = MouseInfo.getPointerInfo().getLocation().y;
System.out.println("x-coordinate="+posx);
               System.out.println("y-coordinate="+posy);
               x=posx;
               y[i]=posy;
               i=i+1;
          ActionListener actionListener = new ActionListener(){
               public void actionPerformed(ActionEvent ae)
                    Object o = ae.getSource();
                    if (o==bn)
                         Graphics g= frame.getGraphics();
                         Graphics2D g2D = (Graphics2D)g;
                         g2D.setComposite(AlphaComposite.getInstance(AlphaComposite.CLEAR, 0.0f));
                         g2D.setColor(Color.red);
                         g2D.drawLine(x[0],y[0],x[1],y[1]);
                         i=0;
          label.addMouseListener(mouseListener);
          bn.addActionListener(actionListener);
frame.add(label, BorderLayout.CENTER);
          bn.setSize(10,10);
          frame.add(bn, BorderLayout.NORTH);
frame.setSize(300, 300);
frame.setVisible(true);

Answer 1

Graphics g= frame.getGraphics();
is your problem
which will appear like this
Graphics g= frame.getGraphics();if you highlight the code, then click the 'code' button, above the editor area
solution is to use a JPanel for your graphics, and override its paintComponent()
JPanel p = new JPanel(){
  public void paintComponent(Graphics g){
    super.paintComponent(g);
    //other graphics stuff here
};