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

public class Rec extends JPanel {
    private int test;

    /* change 'max' and try different values, compilate again after
       each change before running the app */
    private int max = 10;

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        test = 0;
        drawRuler(g, 0, 400, 8);
        g.drawString("A recursion example with graphics", 10, 130);
    }

    private void drawRuler(Graphics g, int left, int right, int level) {

        if (level < 1) return;

        if (test > max) return;

        test++;

        int mid = (left + right) / 2;

        g.drawLine (mid, 110, mid, 110 - level * 10);

        drawRuler (g, left, mid-1, level - 1);
        drawRuler (g, mid + 1, right, level - 1);
    }
    /* each line mentioning 'test' and 'max' may be removed after
       exploring how the recursion works, or else set 'max' to a
       high value */
}