如何在JFrame中居中和扩展JPanel？

Question

I am making a copy of the apple calendar application, and I am having trouble aligning the month name and year name with the center of my screen, while aligning the left and right buttons with the left and right sides of the screen. Here is my code:

final JPanel months = new JPanel();
months.setLayout(new BoxLayout(months,BoxLayout.X_AXIS));
months.add(back, BorderLayout.WEST); //back is a JButton
JLabel monthName = new JLabel(this.monthNames[this.month]+" ", SwingConstants.CENTER); 
JLabel year = new JLabel("" + this.year, SwingConstants.CENTER);
monthName.setFont(new Font("Helvetica", 0, 24));
year.setFont(new Font("Helvetica", 0, 24));
monthName.setHorizontalAlignment(JLabel.CENTER);
months.add(monthName, BorderLayout.CENTER);
months.add(year, BorderLayout.CENTER);
months.add(front, BorderLayout.EAST);
add(months);

Yet it shows up like this:

Answer 1

months.setLayout(new BoxLayout(months,BoxLayout.X_AXIS));

You are using a BoxLayout . A BoxLayout just adds the components horizontally to the panel. The WEST, CENTER, EAST constrains are only used by a BorderLayout so they are ignored by the BoxLayout.

months.add(monthName, BorderLayout.CENTER);
months.add(year, BorderLayout.CENTER);

When using a BorderLayout you can only add a single component to a region of the layout. So if you want to add two components to the CENTER you need to first create a panel and add the components to the panel.

So your basic code might be something like:

JPanel centerPanel = new JPanel();
centerPanel.add(month);
centerPanel.add(year);

JPanel mainPanel = new JPanel( new BorderLayout() );
mainPanel.add(westButton, BorderLayout.WEST);
mainPanel.add(centerPanel, BorderLayout.CENTER);
mainPanel.add(eastButton, BorderLayout.EAST);