import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;



public class FunnyThings {
    static JFrame f = new JFrame("irgendein cooler titel");
    static MyDrawPanel m1;
    //hier bestimmen was gezeichnet wird
    public boolean drawFigureOne = true;
    public boolean drawFigureTwo = true;

    public static void main(String[] args) {
	new FunnyThings().drawGui();

    }

    public void drawGui() {
	m1 = new MyDrawPanel();
	JButton drawBtn = new JButton("Zeichnen");
	drawBtn.addActionListener(new drawBtnListener());
	f.setContentPane(m1);
	f.getContentPane().add(drawBtn);
	f.setBounds(30, 30, 300, 300);
	f.setVisible(true);
	f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public class MyDrawPanel extends JPanel{
	public void paintComponent(Graphics g) {
	    Graphics2D g2 = (Graphics2D)g;


	    //so bestimmn was gezeichnet wird
	    if (drawFigureOne) {
		XQuadrat quad = new XQuadrat(g);
	    }

	   /* if (drawFigureTwo) {
		int r = (int) (Math.random() * 200);
		g.setColor(new Color(r, 0, 0));
		g.fillRect(100, 100, 20, 20);
	    } */

	}

    }

    public class drawBtnListener implements ActionListener {

	@Override
	public void actionPerformed(ActionEvent e) {
	    m1.repaint();

	}

    }
}

// ================================================
// deine figur klassen:
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;

public class XQuadrat {

    public XQuadrat(Graphics g) {
	int r = (int) (Math.random() * 200);
	g.setColor(new Color(r, 0, 0));
	g.fillRect(100, 100, 20, 20);
    }

}