Java：JButton数组不会改变大小

Question

Hey I made 3 for loops to create 3 different arrays of JButtons. Which I then put into a Gridlayout. The left and the right side turn out fine but the center will just fill the panel.

Here is my code for the right side:

        rightPanel = new JPanel();
    rightPanel.setLayout(new GridLayout(12, 4, 5, 5));
    rightPanel.setBorder(new EmptyBorder(10 ,10 ,10 ,10));


    for (int a = 0; a < 12; a++) {
        for (int b = 0; b < 4; b++) {
            battons[b][a] = new feedbackKnop.RechterKnop();
            battons[b][a].setPreferredSize(new Dimension(50, 50));
            rightPanel.add(battons[b][a]);
            battons[b][a].setEnabled(false);
        }
    }

Here is my code for the center:

        btnPanel = new JPanel();
    btnPanel.setLayout(new GridLayout(12, 4, 5, 5));
    btnPanel.setBorder(new EmptyBorder(10 ,10 ,10 ,10));

    for (int i = 0; i < 12; i++) {
        for (int j = 0; j < 4; j++) {
            buttons[j][i] = new KleurenButton("");
            buttons[j][i].setPreferredSize(new Dimension (50, 50));
            btnPanel.add(buttons[j][i]);
            buttons[j][i].setEnabled(false);

        }

    }

I want it to have the size like the circles on the right side

Result:

Answer 1

The GridLayout causes all grids to be the same size, and the BorderLayout expands the center to fill the window. To fix this you need to either enforce the Window Size to be fixed (or at a certain aspect ratio), or pick a different layout that doesn't automatically expand it's components. GroupLayout is very popular.

Answer 2

As commenters have suggested, it is an issue with BorderLayout. BorderLayout has a "greedy" CENTER panel, meaning that by default it will stretch whatever JComponent is in there to the entire size. This is unlike the borders (NORTH, SOUTH, etc.) that will use a preferredSize. That's why your right and left panels are not streched.

A simple solution (without drastic changes to your layouts) might be to add a JPanel to the center, give it a FlowLayout, and then add your Center Grid Panel to that. It's not ideal, but might be a quick way to prototype your view.