Paint Method - Draw Oval In Random Coordination

So I created little program. So window is in full screen. Paint method.
 
package Test;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.*;
import java.util.Random;
public class Main extends JFrame {
Graphics g;

[Code] ....

So, paint method works perfectly. He paint rectangle. Good. But I dont know how using ,,paint2'' method. I need when you press z button, ,,paint2'' method draw Oval in random coordination. So instead ,,paint2'' method i using repaint() but i dont know nothing about paint methods and so on. So how using ,,paint2'' method? Now when i run program, i get a lot of error..