import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.event.*;


public class Main extends JPanel  implements  MouseListener {
    int ax,ay,sx,sy,bx,by;
    int X,Y; //Koordinaten des Mausklicks
    int wieoftGeklickt = 0; //geht bis 3

   public Main(){
				addMouseListener (this);
	}  
    public void mouseEntered(MouseEvent e) {} //nicht verwendete Events
    public void mouseExited(MouseEvent e) {}
    public void mouseReleased(MouseEvent e) {}    
    public void mouseClicked(MouseEvent e){}    

    public void mousePressed(MouseEvent e){    
        wieoftGeklickt++;
        if (wieoftGeklickt == 4) wieoftGeklickt = 1;
        X = e.getX();
        Y = e.getY();
        repaint();
    }
 
    public void paint(Graphics g) {
        g.drawOval(X, Y, 3, 3);
        if (wieoftGeklickt == 1){ //Punkt A
            g.drawString("A", X+5, Y);
            ax=X;ay=Y;
        }
        if (wieoftGeklickt == 2){ //Punkt S
            g.drawString("S", X+5, Y);
            sx=X;sy=Y;
        }
        if (wieoftGeklickt == 3){ //Punkt B, Winkel oder Dreieck fertigstellen
            g.drawString("B", X+5, Y);
            bx=X;by=Y;
            g.drawLine(ax, ay, sx, sy);
            g.drawLine(sx, sy, bx, by);
            //g.drawLine(bx, by, ax, ay); //eventuell übrige Strecke
        }

   }
  
    
    public static void main(String[] args) {
        JFrame frame = new JFrame("Meine Grafik");
      
        frame.getContentPane().add(new Main());
        frame.setSize(600, 450);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
    }
}