Question

Consider the following figure:

I need to develop a swing GUI the looks like this. I simply named them jLabel’s but there a few images and jLabels in it. The default awt background visible is a JPanel and each red background visible is a serperate JPanel. Now I need them to get stacked as shown above. I tried a number of LayoutManagers and still it doesn’t work.

The important point here is that the number of red colored divs are not constant. If there is only one red colored div then it must be displayed at the top, not at the center. As far as i know GridBagLayout should work, but it centers the single red colored jpanel available. All the layout managers are centering them but not stacking them from top to bottom.

Answer 1

Even with anchor set to NORTH then the panels will still be centered. You could work around it by adding a dummy panel to fill the remaining space. Personally I’d stay well away from GridBagLayout though.

JFrame frame = new JFrame();
JPanel content = new JPanel();
content.setBorder(BorderFactory.createLineBorder(Color.red));
frame.setContentPane(content);
frame.getContentPane().setLayout(new GridBagLayout());
frame.setSize(400, 300);

for (int i = 0; i < 3; i++) {
    JPanel panel = new JPanel();
    panel.add(new JLabel("label1"));
    panel.add(new JLabel("label2"));
    panel.add(new JLabel("label3"));
    panel.setBorder(BorderFactory.createLineBorder(Color.red));
    GridBagConstraints con = new GridBagConstraints();
    con.gridy = i;
    con.gridx = 0;
    con.anchor = GridBagConstraints.NORTHWEST;
    con.ipady = 10;
    frame.getContentPane().add(panel, con);
}

// dummy panel to use up the space (force others to top)
frame.getContentPane().add(
        new JPanel(),
        new GridBagConstraints(0, 3, 1, 1, 1, 1,
                GridBagConstraints.NORTHWEST,
                GridBagConstraints.VERTICAL, new Insets(0, 0, 0, 0), 0,
                0));

frame.setVisible(true);

GroupLayout example (my favourite layout manager).

JFrame frame = new JFrame();
JPanel content = new JPanel();
frame.setContentPane(content);
frame.getContentPane().setLayout(
        new BoxLayout(content, BoxLayout.Y_AXIS));
frame.setSize(400, 300);
GroupLayout gLayout = new GroupLayout(content);
content.setLayout(gLayout);
ParallelGroup hGroup = gLayout.createParallelGroup();
gLayout.setHorizontalGroup(hGroup);
SequentialGroup vGroup = gLayout.createSequentialGroup();
gLayout.setVerticalGroup(vGroup);
for (int i = 0; i < 3; i++) {
    JPanel panel = new JPanel();
    panel.add(new JLabel("label1"));
    panel.add(new JLabel("label2"));
    panel.add(new JLabel("label3"));
    panel.setBorder(BorderFactory.createLineBorder(Color.red));
    hGroup.addComponent(panel);
    vGroup.addComponent(panel, GroupLayout.PREFERRED_SIZE,
            GroupLayout.PREFERRED_SIZE, GroupLayout.PREFERRED_SIZE);
    vGroup.addGap(10);
}

frame.setVisible(true);