I tried to place the components (ex: button) in a container using GridBagConstraints. But I found an empty area between the elements. I tried to modify the various parameters but I cannot find the solution.
I want to remove this blank area (for example, button 8 should be next to the right of buttons 4, 6, 7).
Thank you
import java.awt.*;
import javax.swing.JButton;
import javax.swing.JFrame;
public class GridBagLayout8Button {
public static void addComponentsToPane(Container pane) {
pane.setLayout(new GridBagLayout());
GridBagConstraints gbc1 = new GridBagConstraints();
GridBagConstraints gbc2 = new GridBagConstraints();
GridBagConstraints gbc3 = new GridBagConstraints();
GridBagConstraints gbc4 = new GridBagConstraints();
GridBagConstraints gbc5 = new GridBagConstraints();
GridBagConstraints gbc6 = new GridBagConstraints();
GridBagConstraints gbc7 = new GridBagConstraints();
GridBagConstraints gbc8 = new GridBagConstraints();
JButton button1 = new JButton("1");
gbc1.anchor = GridBagConstraints.NORTHWEST;
gbc1.gridx = 0;
gbc1.gridy = 0;
gbc1.gridwidth = 1;
gbc1.gridheight = 2;
button1.setPreferredSize(new Dimension(46, 82));
pane.add(button1, gbc1);
JButton button2 = new JButton("2");
gbc2.anchor = GridBagConstraints.NORTHWEST;
gbc2.gridx = 1;
gbc2.gridy = 0;
gbc2.gridwidth=1;
gbc2.gridheight=1;
button2.setPreferredSize(new Dimension(118, 41));
pane.add(button2, gbc2);
JButton button3 = new JButton("3");
gbc3.anchor = GridBagConstraints.NORTHWEST;
gbc3.gridx = 1;
gbc3.gridy = 1;
gbc3.gridwidth=1;
gbc3.gridheight=1;
button3.setPreferredSize(new Dimension(118, 41));
pane.add(button3, gbc3);
JButton button4 = new JButton("4");
gbc4.anchor = GridBagConstraints.NORTHWEST;
gbc4.gridx = 2;
gbc4.gridy = 0;
gbc4.gridwidth = 2;
gbc4.gridheight = 2;
button4.setPreferredSize(new Dimension(164, 82));
pane.add(button4, gbc4);
JButton button5 = new JButton("5");
gbc5.anchor = GridBagConstraints.NORTHWEST;
gbc5.gridx = 0;
gbc5.gridy = 2;
gbc5.gridwidth=3;
gbc5.gridheight=2;
button5.setPreferredSize(new Dimension(246, 82));
pane.add(button5, gbc5);
JButton button6 = new JButton("6");
gbc6.anchor = GridBagConstraints.NORTHWEST;
gbc6.gridx = 3;
gbc6.gridy = 2;
gbc6.gridwidth=1;
gbc6.gridheight=1;
button6.setPreferredSize(new Dimension(82, 41));
pane.add(button6, gbc6);
JButton button7 = new JButton("7");
gbc7.anchor = GridBagConstraints.NORTHWEST;
gbc7.gridx = 3;
gbc7.gridy = 3;
gbc7.gridwidth=1;
gbc7.gridheight=1;
button7.setPreferredSize(new Dimension(82, 41));
pane.add(button7, gbc7);
JButton button8 = new JButton("8");
gbc8.anchor = GridBagConstraints.NORTHWEST;
gbc8.gridx = 4;
gbc8.gridy = 0;
gbc8.gridwidth=1;
gbc8.gridheight=4;
button8.setPreferredSize(new Dimension (41, 164));
pane.add(button8, gbc8);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
JFrame frame = new JFrame("GridBagLayout Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addComponentsToPane(frame.getContentPane());
frame.pack();
frame.setVisible(true);
}
});
}
}
The issue is that the GridBagLayout doesn't know how to allocate a width to a column unless at least one component is added to the column with a "gridwidth = 1".
In this case the issue is between buttons 4 and 5:
Run you code removing button 4 from the layout:
//pane.add(button4, gbc4);
The layout is compressed.
Now look at button 5 with a width of 246.
This indicates the width of the first 3 columns should be at least 246.
Buttons 1 and 2 only have widths of 46 and 118 for a total of 164, which implies that column 2 should have a width of 82 (246 - 164).
However, the GridBagLayout is using 0, for the width of the column. This somehow is then adding the extra 82 pixels of space after button 4 leaving the gap between it and button 8.
The solution is to give column2 a minimum width. So even if no component with a gridwidth =1 is added to the column, a non-zero default width can be used in the calculations.
This is done with the following code:
//pane.setLayout(new GridBagLayout());
GridBagLayout gbl = new GridBagLayout();
pane.setLayout(gbl);
// Set up a layout with 5 columns.
// minimimum width of a column 2 is 82 pixels
int[] columns = new int[5];
columns[2] = 82;
gbl.columnWidths = columns;
This is not really a solution because it is to manual to attempt to calculate the minimum width.
It is only an attempt at an explanation of what is happening. The concept of applying minimum values to columns can be useful in other situations. See: Creating a board game layout using JLayeredPane for a working example of this concept.
Note, when you use the "fill" constraint as suggested by VGR then buttons 4, 6, 7 will be increased in size by an extra 82 pixels. So this addresses the visual gap by increasing the preferred widths of the buttons affected.
Without knowing the actual requirement and why such weird preferred sizes are being used we can't really give a better solution.
Edit:
the size of the buttons (height, width) is used to represent somes values, so it's important to maintain as they are
Then you may need so use nested panel with different layout managers to achieve you desired layout.
For example you might have a parent panel with a BorderLayout. Then you use create a panel with buttons 1-7 using your existing code and add this panel to the BorderLayout.CENTER. Then you add button 8 to the BorderLayout.LINE_END.