How do I resize these panels in my JFrame?

Question

I'm creating a chess game where the main panel is using BorderLayout, there is a panel at NORTH for buttons, a panel at CENTER for the board itself (set to GridLayout) and a sidebar at East.

I have made the JFrame unresizable and I'd like the chessboard to fit the panels in so that the East panel is a lot wider (maybe 200 pixels) and the board remains a square. I can't figure out how to change the sizes of these components individually.

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

public class GameWindow extends JFrame {

    private final JPanel playArea = new JPanel(new BorderLayout(3,3));
    private final JButton[][] boardSquares = new JButton[8][8];
    private final JPanel board;
    private final JPanel sidebar = new JPanel();
    private final JLabel message = new JLabel("Game by ...");

    public  GameWindow() {
        playArea.setBorder(new EmptyBorder(5, 5, 5, 5));

        JToolBar tools = new JToolBar();


        tools.setFloatable(false);
        playArea.add(tools, BorderLayout.PAGE_START);
        tools.add(new JButton("New Game"));
        tools.add(new JButton("Save"));
        tools.add(new JButton("Restore")); 
        tools.addSeparator();
        tools.add(new JButton("Resign"))
        tools.addSeparator();
        tools.add(message);

        board = new JPanel(new GridLayout(0, 8));
        board.setBorder(new LineBorder(Color.BLACK));
        playArea.add(board, BorderLayout.CENTER);
        playArea.add(sidebar, BorderLayout.EAST);

        Insets buttonMargin = new Insets(0,0,0,0);
        for (int i = 0; i < boardSquares.length; i++) {
           for (int j = 0; j < boardSquares[i].length; j++) {
                JButton square = new JButton();
                square.setMargin(buttonMargin);
                if ((i+j)%2 == 0) {
                    square.setBackground(Color.WHITE);
                } 
                else {
                    square.setBackground(Color.BLACK);
                }
                board.setSize(600, 600);
                board.add(boardSquares[j][i] = square);
            }
        }
    }

    public final JComponent getChessBoard() {
    return board;
    }

    public final JComponent getGui() {
        return playArea;
    }

    public static void main(String[] args) {

        GameWindow window = new GameWindow();

        JFrame frame = new JFrame("Checkers");
        frame.setResizable(false);
        frame.add(window.getGui());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationByPlatform(true);
        frame.setSize(800, 800);

        frame.setVisible(true);
    }
}

Answer 1

Firstly, since JDK 1.4, Java is encouraging the use of BorderLayout constants as BorderLayout.PAGE_START, BorderLayout.LINE_START, BorderLayout.CENTER, BorderLayout.LINE_END and BorderLayout.PAGE_END over the latter used by you.

Secondly you can simply override, the getPreferredSize() of the said JPanel, in order for it to give, some size that you feel like will work for your use case. Use of setPreferredSize() is restricted, since, not all LayoutManagers use to respect the Dimension specified by it.

Hence you could do something like:

private final JPanel sidebar = new JPanel() {
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(100, 100);
    }
};

You can try this modified code:

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

public class GameWindow extends JFrame {

    private final JPanel playArea = new CustomPanel(710, 710);  
    private final JButton[][] boardSquares = new JButton[8][8];
    private final JPanel board;
    private final JPanel sidebar = new CustomPanel(100, 100);
    private final JLabel message = new JLabel("Game by ...");

    public  GameWindow() {
        playArea.setLayout(new BorderLayout(3,3));
        playArea.setBorder(new EmptyBorder(5, 5, 5, 5));

        JToolBar tools = new JToolBar();


        tools.setFloatable(false);
        playArea.add(tools, BorderLayout.PAGE_START);
        tools.add(new JButton("New Game"));
        tools.add(new JButton("Save"));
        tools.add(new JButton("Restore")); 
        tools.addSeparator();
        tools.add(new JButton("Resign"));
        tools.addSeparator();
        tools.add(message);

        board = new CustomPanel(600, 600);
        board.setLayout(new GridLayout(0, 8));
        board.setBorder(new LineBorder(Color.BLACK));
        playArea.add(board, BorderLayout.CENTER);
        playArea.add(sidebar, BorderLayout.LINE_START);

        Insets buttonMargin = new Insets(0,0,0,0);
        for (int i = 0; i < boardSquares.length; i++) {
           for (int j = 0; j < boardSquares[i].length; j++) {
                JButton square = new JButton();
                square.setOpaque(true);
                square.setMargin(buttonMargin);
                if ((i+j)%2 == 0) {
                    square.setBackground(Color.WHITE);
                } 
                else {
                    square.setBackground(Color.BLACK);
                }
                board.add(boardSquares[j][i] = square);
            }
        }
    }

    private class CustomPanel extends JPanel {
        private int width;
        private int height;

        public CustomPanel(int width, int height) {
            this.width = width;
            this.height = height;
            setOpaque(true);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(width, height);
        }
    }

    public final JComponent getChessBoard() {
    return board;
    }

    public final JComponent getGui() {
        return playArea;
    }

    public static void main(String[] args) {

        GameWindow window = new GameWindow();

        JFrame frame = new JFrame("Checkers");
        frame.setResizable(false);
        frame.setContentPane(window.getGui());
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.setLocationByPlatform(true);
        frame.pack();

        frame.setVisible(true);
    }
}

Moreover, before setting the background of JButton, it would be wise to call button.setOpaque(true) property.