DrawShapes.java

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;

public class DrawStuff {
    private JFrame frame;

    public DrawStuff() {
        frame = new JFrame("Sierpinski Triangle");
        frame.setSize(1024, 768);
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setPreferredSize(frame.getSize());
        frame.add(new DrawShapes(frame.getSize()));
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String... argv) {
        new DrawStuff();
    }

    public static class DrawShapes extends JPanel {
        int startX = 100;
        int startY = 400;
        int startSide = 300;
        public DrawShapes(Dimension dimension) {
            setSize(dimension);
            setPreferredSize(dimension);
        }

        @Override
        public void paintComponent(Graphics g) {
            Graphics2D g2 = (Graphics2D)g;
            Dimension d = getSize();


            drawTriangle(g2, startX, startY, startSide);
        }

        private void drawTriangle(Graphics2D g, int x, int y, int side) {
            g.drawLine(x, y, x + (side/2), y - side);
            g.drawLine(x + (side/2), y - side, x + side, y);
            g.drawLine(x, y, x + side, y);
            
            

        }
    }

}