Рисование jframe & jpanel

package paintingandstroking;
import java.awt.*;
import java.awt.geom.*;
import java.awt.Polygon;
import java.awt.Dimension;
import javax.swing.JLabel;
//import java.awt.Toolkit;
import javax.swing.JFrame;
public class PaintingAndStroking
    extends  JFrame{
  public static void main(String[] args) {
    PaintingAndStroking f = new PaintingAndStroking();
    f.setTitle("PaintingAndStroking v1.0");
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    int height = screenSize.height;
    int width = screenSize.width;
    f.setSize(600, 300);
    f.setLocation(width/2 - 300, height/2 - 150);
    f.setDefaultCloseOperation(EXIT_ON_CLOSE);
    f.setResizable(false); 
    f.setVisible(true);
    
    
    
  }
  
  @Override
  public void paint(Graphics g) {
    Graphics2D g2 = (Graphics2D)g;
    int[] X = {0, 5, 100, 0};
    int[] Y = {0, 150, 100, 0};
    Polygon mypoly = new Polygon(X, Y, 4);
    
    g2.setStroke(new BasicStroke(5));
    g2.draw(mypoly);
    g2.fill(mypoly);
}
}

public static void main(String[] args) {
          javax.swing.SwingUtilities.invokeLater(new Runnable() {
               public void run() {
                    JFrame.setDefaultLookAndFeelDecorated(true);
                    createGUI();
               }
          });
     }