Recursion

class Recursion {

    static int sum(int a, int b) {
        if (b == 0) return a;
        return sum(++a, --b);
    }

    static void times(int i) {
        if (i == 0) return;
        System.out.println("i: " + i);
        times(--i);
    }

    public static void main(String[] args) {
        
        // Summing two numbers
        System.out.println(sum(6, 9));
        
        // Iteration without a loop
        times(10);
    
    }
}

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

public class Main {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            new TreeFrame();
        });
    }
}

class TreeFrame extends JFrame {

    public TreeFrame() {
        setSize(new Dimension(1024, 768));
        setVisible(true);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }

    public void paint(Graphics g) {
        super.paint(g);
        // Starting point
        int xFrom = 512;
        int yFrom = 768;
        // Length of a brunch
        int radius = 100;
        // Starting angle
        double angle = Math.PI;

        // Drawing
        draw(g, xFrom, yFrom, radius, angle);
    }

    private void draw(Graphics g, int xFrom, int yFrom, double radius, double angle) {

        double deltaAngle = 0.25;

        double leftEndX = xFrom + Math.sin(angle + deltaAngle)*radius;
        double leftEndY = yFrom + Math.cos(angle + deltaAngle)*radius;

        g.setColor(Color.BLACK);
        g.drawLine(xFrom, yFrom, (int)leftEndX, (int)leftEndY);
    }
}