Hey guys I want to add class object to JPanel where they could be drag'n'dropped . But when I add the object it doesnt shw. When I add it to JFrame without layout it shows normally. What should I do?

public class Interface extends JPanel {

private static final long serialVersionUID = -1383023567823358737L;
static JFrame f = new JFrame();
JButton btn1;

public static void main(String[] args) {
Interface frame = new Interface();
frame.setVisible(true);
}

public Interface() {
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(400,400);
JPanel panel_1 = new JPanel();
panel_1.setBorder(BorderFactory.createLineBorder(Color.black, 2));
f.add(panel_1);
Dragging bus = new Dragging();
panel_1.add(bus);
f.pack();
f.setVisible(true);

}