为什么只有1个JButton显示？

Question

I don't understand why only "Log in to existing account" is the only button to show. All I want is 2 buttons to show and "Create account" isn't showing even though I set its visibility to true and moved it so it isn't overlapping with "Login to existing account".

public class HotelBookingSystem extends JFrame
{
Container con;
public HotelBookingSystem()
{
    super("Booking System");
    JFrame mainWindow = new JFrame("Booking");
    mainWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    mainWindow.setSize(350,400);
    mainWindow.setVisible(true);

    con = getContentPane();
    BorderLayout myLayout = new BorderLayout();
    con.setLayout(myLayout);

    JButton login = new JButton ("Login to existing account");
    JButton register = new JButton ("Create Account");
    JPanel loginPanel = new JPanel();
    JPanel registerPanel = new JPanel();

    loginPanel.add(login, BorderLayout.NORTH);
    registerPanel.add(register, BorderLayout.SOUTH);
    login.setSize(350, 100);
    register.setSize(350, 100);

    loginPanel.setVisible(true);
    registerPanel.setVisible(true);

    mainWindow.add(login);
    mainWindow.add(register);
    mainWindow.add(loginPanel);
    mainWindow.add(registerPanel);

    login.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
              mainWindow.setVisible(false);     
            }
        });

    register.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
              mainWindow.setVisible(false);     
            }
        });
}

public static void main(String[] args) 
{
    HotelBookingSystem dataBaseAccess = new HotelBookingSystem();
}

}

Answer 1

Have you tried using a different layout for the panels containing the JButtons?

Since you have two different panels, one button is on the very top of loginPanel, and the other button is on the very bottom of registerPanel.

Instead, try putting them in the same panel, were one is in the NORTH and the other is in the CENTER.

Answer 2

Many problems:

mainWindow.setVisible(true);

The frame should be made visible AFTER all the components are added to the frame, so this should be the last statement in the constructor.

con = getContentPane();
BorderLayout myLayout = new BorderLayout();
con.setLayout(myLayout);

The default layout manager for the content pane of a JFrame is a BorderLayout, so this code is unnecessary.

login.setSize(350, 100);
register.setSize(350, 100);

Don't try to set the size of a component. It is the job of the layout manager to set the size and location of each component.

JPanel loginPanel = new JPanel();
JPanel registerPanel = new JPanel();

loginPanel.add(login, BorderLayout.NORTH);
registerPanel.add(register, BorderLayout.SOUTH);

Why are you creating two panels? You can just add the buttons directly to the frame.

Also, the default layout manager for a JPanel is the FlowLayout. So you can't just a BorderLayout constraint and expect it to work.

loginPanel.setVisible(true);
registerPanel.setVisible(true);

All Swing component (except JFrame, JDialog etc) are visible by default, so the above code is unnecessary.

mainWindow.add(login);
mainWindow.add(register);
mainWindow.add(loginPanel);
mainWindow.add(registerPanel);

As mentioned earlier the default layout for the frame is a BorderLayout. If you don't specify a constraint, then the component goes to the "CENTER". But only a single component can be displayed in the center at one time.

Fix all the other problems and then try something like:

mainWindow.add(login, BorderLayout.NORTH);
mainWindow.add(register, BorderLayout.SOUTH);
mainWindow.add(loginPanel, BorderLayout.WEST);
mainWindow.add(registerPanel, BorderLayout.EAST);

to see the difference. Adjust the constraints as required.

I suggest you read the section from the Swing tutorial on Layout Manager for working examples to give you the basics of using each of the layout managers.