A component takes up only one column in a GridBagLayout

Question

I am trying to make quite a simple layout, which would be really easy in some other layout manager. However, I need to get it working for GridBagLayout. After a snippet of code:

GridBagConstraints c = new GridBagConstraints();

JPanel smallLogoPanel = new JPanel();
smallLogoPanel.setBorder(new LineBorder(Color.red, 1));//for visualizing components' display are
smallLogoPanel.setSize(50, 50);
c.gridx = 0;
c.gridy = 0;
c.gridwidth = 1;
c.gridheight = 2;
c.weightx = 0.01;
c.weighty = 0.1;
c.fill = GridBagConstraints.BOTH;

JLabel smallLogoLabel = new JLabel(some code to get ImageIcon);
smallLogoPanel.add(smallLogoLabel);
this.infoPanel.add(smallLogoPanel, c);

JLabel label1 = new JLabel("Label 1");
label1.setFont(new Font("Verdana", Font.BOLD, 30));
label1.setBorder(new LineBorder(Color.red, 1));
c.gridx = 1;
c.gridy = 0;
c.gridwidth = 9;
c.gridheight = 1;
c.weightx = 0.99;//for some reason smallLogoLabel takes much more space if this weightx is any smaller
c.weighty = 0.075;
this.infoPanel.add(label1, c);

JLabel label2 = new JLabel("Label 2");
label2.setFont(new Font("Verdana", Font.BOLD, 10));
label2.setBorder(new LineBorder(Color.red, 1));
c.gridx = 1;
c.gridy = 1;
c.gridwidth = 9;
c.gridheight = 1;
c.weightx = 0.99;
c.weighty = 0.025;
this.infoPanel.add(label2, c);

... I get such a result:

... which is absolutely fine. The problem is when I add two more labels below it:

JLabel label3 = new JLabel("Label 3");
label3.setFont(new Font("Verdana", Font.BOLD, 20));
label3.setBorder(new LineBorder(Color.red, 1));
c.gridx = 0;
c.gridy = 2;
c.gridwidth = 5;
c.gridheight = 1;
c.weightx = 0.5;
c.weighty = 0.05;
c.anchor = GridBagConstraints.CENTER;
this.infoPanel.add(label3, c);

JLabel label4 = new JLabel("Label 4");
label4.setFont(new Font("Verdana", Font.BOLD, 20));
label4.setBorder(new LineBorder(Color.red, 1));
c.gridx = 5;
c.gridy = 2;
c.gridwidth = 5;
c.gridheight = 1;
c.weightx = 0.5;
c.weighty = 0.05;
c.insets.left = 0;
this.infoPanel.add(label4, c);

...the result looks like:

Widths of top row become different, particularly panel with icon becomes wider. Another issue - bottom row. I expected both labels to be of an equal width. However, it seems the left one takes up only 1 column which is of the same width as the panel with icon.

I would be really glad I anyone could help me with this one as I am totally stuck now.

Answer 1

All components in a single column of a GridBagLayout have exactly the same weightx: The maximum weightx of any GridBagConstraints belonging to any component in that column.

Initially, the weightx of column 0 was 0.01. But then you added something else in column 0, on a different row, with a weightx of 0.5, so now all components in column 0 are treated by GridBagLayout as if they have a weightx of 0.5.

The same rules apply to rows and weighty values.

By the way, it is a common misconception that gridwidth = 9 can make a cell nine times wider than it would be if its constraints were just gridwidth = 1. That is not what actually happens. A gridwidth of 9 will not be any wider, unless another row actually contains non-empty cells in the those columns. This is because GridBagLayout cell sizes are flexible, and their width is zero unless they contain components. Only weights determine relative size of cells. gridwidth and gridheight do not.