GridBagLayout gridwidth doesn’t work as expected

I’m working with the java swing LayoutManager GridBagLayout, and ran into this problem. I want a layout like this

ACC
BB

But get a layout like this

ACC
B

A and B take up the same number of columns despite B having a gridwidth of 2 where A’s gridwidth is 1. I don’t think there can be a vanishingly small column between A,B and C because C starts in column 1. The problem does not occur if C’s gridwidth is 1 instead of 2. I’m baffled by the output.

Why is this happening / how can I fix this?

JFrame test = new JFrame();
test.setSize(800,800);
test.setLayout(new GridBagLayout());
test.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

GridBagConstraints c;

c = new GridBagConstraints();
c.gridx=0;
c.gridy=0;
c.fill = GridBagConstraints.BOTH;
c.weightx = 1;
c.weighty = 1;
test.add(new JButton("A"), c);

c = new GridBagConstraints();
c.gridx=0;
c.gridy=2;
c.gridwidth=2;
c.fill = GridBagConstraints.BOTH;
c.weightx = 1;
c.weighty = 1;
test.add(new JButton("B"), c);

c = new GridBagConstraints();
c.gridx=1;
c.gridy=0;
c.gridwidth=2;
c.gridheight=2;
c.fill = GridBagConstraints.BOTH;
c.weightx = 2;
c.weighty = 2;
test.add(new JButton("C"), c);

test.setVisible(true);

Answer

I know how you feel… It seems GridBagLayout reduces the width of columns to 0 when they are not filled by 1×1 component. I don’t know if the following is the most efficient solution, but it works (by adding two dummy JPanel to “inflate” columns 1 and 2):

JFrame test = new JFrame();
test.setSize(800,800);
test.setLayout(new GridBagLayout());
test.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

GridBagConstraints c;

c = new GridBagConstraints();
c.gridx=0;
c.gridy=0;
c.fill = GridBagConstraints.BOTH;
c.weightx = 1;
c.weighty = 1;
test.add(new JButton("A"), c);

c = new GridBagConstraints();
c.gridx=0;
c.gridy=1;
c.gridwidth=2;
c.fill = GridBagConstraints.BOTH;
c.weightx = 1;
c.weighty = 1;
test.add(new JButton("B"), c);

c = new GridBagConstraints();
c.gridx=1;
c.gridy=0;
c.gridwidth=2;
c.gridheight=1;
c.fill = GridBagConstraints.BOTH;
c.weightx = 2;
c.weighty = 2;
test.add(new JButton("C"), c);

c = new GridBagConstraints();
c.gridx=1;
c.gridy=2;
c.gridwidth=1;
c.gridheight=0;
c.fill = GridBagConstraints.HORIZONTAL;
c.weightx = 1;
c.weighty = 0;
test.add(new JPanel(), c);

c = new GridBagConstraints();
c.gridx=2;
c.gridy=3;
c.gridwidth=1;
c.gridheight=0;
c.fill = GridBagConstraints.HORIZONTAL;
c.weightx = 1;
c.weighty = 0;
test.add(new JPanel(), c);

test.setVisible(true);