JFrame frame = new JFrame();
JFrame frame2 = new JFrame();

frame.setTitle("Title name");
frame.setSize(600, 600);
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.getContentPane().setBackground(Color.RED);
frame.setVisible(true);

frame2.setUndecorated(true);
frame2.setLocationRelativeTo(frame);
frame2.getContentPane().setBackground(Color.BLACK);
frame2.setVisible(true);