Confused about awt and swing in java

Question

I am working in java with SWING and AWT components. I am confused about layouts in it. I have add a panel and add buttons inside that panel using setBounds(), then add this panel to a frame which is using flow layout. But the panel is not been able to display itself.. Here is my code:

public class MainWindow implements ActionListener {
    private JFrame frame;
    private JPanel panel;
    private JButton play;
    private JButton exit;

    public MainWindow() {
        frame = new JFrame();
        panel = new JPanel();

        play = new JButton(new ImageIcon("button.png"));
        exit = new JButton(new ImageIcon("exit.png"));

        panel.setLayout(null);
        play.setBounds(200, 200, 90, 40);
        exit.setBounds(200, 300, 90, 40);
        panel.setBackground(new Color(45, 204, 112));
        play.addActionListener(this);
        exit.addActionListener(this);
        panel.add(play);
        panel.add(exit);

        Container cont = frame.getContentPane();
        cont.setLayout(new FlowLayout());
        cont.add(panel);

        frame.setSize(800, 700);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }