Ajuda com exercício Deitel

import java.awt.Graphics;
import javax.swing.JPanel;

public class DrawPanel extends JPanel {

    public void paintCompanent(Graphics g) {
        super.paintComponent(g);
        
        int width = getWidth();
        int height = getHeight();
        g.drawLine(0, 0, width, height);
        g.drawLine(0, height, width, 0);
    }
}

import javax.swing.JFrame;

public class DrawPanelTest {

    public static void main(String[] args) {
        DrawPanel panel = new DrawPanel();
        JFrame application = new JFrame();
        application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        application.add (panel);
        application.setSize(250, 250);
        application.setVisible(true);
    }
}