Question

In the following GridBagLayout code, I’m expecting the specified minimum size of JButton btn2 to be respected when the JFrame is resized to be made smaller. But when I make the JFrame smaller, the btn2 gets smaller than its minimum size and then vanishes.

Can someone point me in the right direction of what I’m doing wrong? Maybe I have to set the minimum size of the JPanel that contains the buttons?

Any help is appreciated, thanks!

    JFrame frame = new JFrame();
    frame.setSize(400,300);
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JPanel panel = new JPanel();
    panel.setMinimumSize(new Dimension(400,300));
    panel.setBackground(Color.RED);

    panel.setLayout(new GridBagLayout());
    GridBagConstraints gbc = null;

    JButton btn1 = new JButton("btn1");
    btn1.setPreferredSize(new Dimension(150,50));
    btn1.setMinimumSize(new Dimension(150,50));
    gbc = new GridBagConstraints(0, 0, 1, 1, 0.0, 0.0, 
            GridBagConstraints.NORTHWEST, GridBagConstraints.NONE,
            new Insets(0,0,0,0), 0, 0);
    panel.add(btn1, gbc);

    JButton btn2 = new JButton("btn2");
    btn2.setPreferredSize(new Dimension(150,150));
    btn2.setMinimumSize(new Dimension(150,150));
    gbc = new GridBagConstraints(1, 0, 1, 1, 1.0, 1.0, 
            GridBagConstraints.NORTHWEST, GridBagConstraints.BOTH,
            new Insets(0,0,100,100), 0, 0);
    panel.add(btn2, gbc);

    frame.getContentPane().add(panel);
    frame.setVisible(true);

Answer 1

Maybe I have to set the minimum size of the JPanel that contains the buttons?

AFAIR GBL was notorious for ignoring sizing hints. No, a correction on that. To get sensible resizing of components within GBL, use the GridBagConstraints with appropriate values. Beware though, the behavior of the layout to not display any component that would be forced to less than its minimum size.

I would pack() the frame then set the minimum size on the frame. Here is how it might look, changing the last line to..

frame.pack();
frame.setVisible(true);
frame.setMinimumSize(frame.getSize());

Given the layout though, I would tend to put btn1 into the PAGE_START of the BorderLayout of a panel that is then added to the LINE_START of another BL. btn2 would go in the CENTER of the outer BL.