我正在尝试使用java中的画线和画椭圆

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

public class LineExample extends JPanel {
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawLine(50, 50, 200, 200);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Line Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new LineExample());
        frame.setSize(300, 300);
        frame.setVisible(true);
    }
}

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

public class OvalExample extends JPanel {
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawOval(50, 50, 200, 100);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Oval Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new OvalExample());
        frame.setSize(300, 300);
        frame.setVisible(true);
    }
}