public void paint(Graphics2D pen) {
        for (Spring s : mySprings) {
            s.paint(pen);
        }
        for (ArrayList<Mass> masses: myAssembly) {
        	for (Mass m : masses) {
                m.paint(pen);
            }
        }
        if (myMouseSpring != null) {
        	myMouseSpring.paint(pen);
        }
        if (myMouseMass != null) {
        	myMouseMass.paint(pen);
        }
    }