Question

I need to display chessboard. I have a BoardPanel class which extends JPanel and a GamePanel (also extending JPanel) class containing BoardPanel. GamePanel fills all the application frame.

I want BoardPanel to always be a square with size equal to the minimum of GamePanel’s width and height (if GamePanel’s width is greater than height there should be empty space on the left and right, if it’s smaller there should be empty space on top and bottom). It’s also important that BoardPanel should be displayed in the center of parent panel.

I wrote sth like this:

public GamePanel() {
    setLayout(new BorderLayout(0, 0));
    boardPanel = new BoardPanel(...);
    this.add(boardPanel, BorderLayout.CENTER);
    ...
}

and in BoardPanel:

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    int size = Math.min(this.getParent().getHeight(), this.getParent().getWidth());
    this.setSize(size, size);
    ...
}

It resizes well, but chessboard is always displayed in top left corner of GamePanel (all the empty space is displayed on bot or right) and I don’t know how to fix it.

Any help? Thanks in advance!

Answer 1

Center it using a GridBagLayout.

import java.awt.*;
import javax.swing.*;

public class CenteredPanel {

    public static void main(String[] args) {
        Runnable r = new Runnable() {
            @Override
            public void run() {
                JPanel gui = new JPanel(new GridBagLayout());
                JPanel square = new SquarePanel();
                square.setBackground(Color.RED);
                gui.add(square);

                JFrame f = new JFrame("SquareBoard");
                f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                f.setLocationByPlatform(true);
                f.add(gui);
                f.setMinimumSize(new Dimension(400,100));
                f.pack();
                f.setVisible(true);
            }
        };
        SwingUtilities.invokeLater(r);
    }
}

class SquarePanel extends JPanel {
    @Override
    public Dimension getPreferredSize() {
        Container c = this.getParent();
        int size = Math.min(c.getHeight(), c.getWidth());
        Dimension d = new Dimension(size,size);
        return d;
    }
}