Например, вот так:
final JFrame Hauptfenster = new JFrame();
Hauptfenster.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Hauptfenster.setSize(new Dimension(500, 500));


Hauptfenster.getToolkit().setDynamicLayout(true);
Hauptfenster.setResizable(true);

Container contentPane = Hauptfenster.getContentPane();
contentPane.setLayout(null);


final JPanel panel = new JPanel();
final JPanel panel0 = new JPanel();
Hauptfenster.addComponentListener(new ComponentAdapter(){
@Override
public void componentResized(java.awt.event.ComponentEvent e){
panel.setSize(Hauptfenster.getSize().width / 2, Hauptfenster.getSize().height / 2);
panel0.setSize(Hauptfenster.getSize().width / 2, Hauptfenster.getSize().height / 2);
Hauptfenster.validate();
}
});

panel.add(new JButton("Hi"));

panel.setBackground(Color.blue);
contentPane.add(panel);
panel.setBounds(200, 200,200,200);

panel0.setBorder(new LineBorder(Color.green));
panel0.setBackground(Color.green);
contentPane.add(panel0);
panel0.setBounds(10, 10,200,200);

Hauptfenster.setVisible(true);