import java.awt.*;

public class BullsEye {
    public static void main(String[] args) {
        DrawingPanel panel = new DrawingPanel(500, 500);
        panel.setBackground(Color.WHITE);
        Graphics g = panel.getGraphics();
        
        g.setColor(Color.BLACK);
        g.drawOval(230, 240, 20, 20);
        g.drawOval(220, 230, 40, 40);
        g.drawOval(210, 220, 60, 60);
        g.drawOval(200, 210, 80, 80);
        g.drawOval(190, 200, 100, 100);
        g.drawOval(180, 190, 120, 120);
        g.drawOval(170, 180, 140, 140);
        g.drawOval(160, 170, 160, 160);
        g.drawOval(150, 160, 180, 180);
        g.drawOval(140, 150, 200, 200);
    }
}

import java.awt.*;
import javax.swing.*;

public class BullsEye extends JPanel {
    public static void main(String args[]) {

          // Create our JFrame (main window) and make it 300 x 300
          JFrame frame = new JFrame("BullsEye");
          frame.setSize(300,300);
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    
          // Create an instance of our class and add it to the frame
          BullsEye eye = new BullsEye();
              frame.add(eye);
              frame.setVisible(true);
    }

    // This method fires to draw our circles when we go to paint it on the frame
    public void paintComponent(Graphics g) {
           super.paintComponent(g);
  
           g.setColor(Color.BLACK);

           // Here is your loop. I started with the smallest x value (20)
           // Your Y value of course is 10 greater than X for each iteration
           // Lastly we start the end point at 220 so first one drawn is 200 and decrements 20 each time
           // Since the endpoint x and y are the same, I just used one variable to represent both

           int endpoint = 220;
           for (int x = 20; x <= 110; x += 10) {
                endpoint = endpoint - 20;
                int y = x + 10;
                g.drawOval(x,y,endpoint,endpoint);
           }

    }
}