I've found two ways to do something like you want; centering the buttons turns out to be something that Swing does not make as easy as it might, but then centering components is probably not as common as other alignments.
You can center components in a FlowLayout; the disadvantage in a FlowLayout is that, if the user shrinks the window to the point the components no longer fit, the layout wraps the components. This is very useful for some things, but not for your football players. I've wrapped my example in a scrollpane so this won't happen.
The other way to center components is with GroupLayout, but GroupLayout is not good for the overall layout you are trying to achieve. GroupLayout is intended for use where you have overall rows and columns in which to line things up, and your four lines of football players are not lined up that way vertically, only horizontally. But you can use the centering characteristic of GroupLayout to do the horizontal centering, and make a separate GroupLayout for each line.
My example uses FlowLayout for the first line, and GroupLayout for the second, just to show how it could be done. I did not address the problem of the gap that appears between the players' lines when the window is made large enough. Especially for examples, I do not use the style of tacking method invocations onto other method invocations and constructors; I think the deeply nested parentheses and non-straightforward logic of this style makes it more difficult to figure out (or keep track of) what's going on.
You can use GridBagLayout to center things, also, but I don't use it at all if anything else will do what I need.
I hope this answers your question.
package grouplayout;
import java.awt.FlowLayout;
import javax.swing.BoxLayout;
import javax.swing.GroupLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
public class Main2 extends JFrame
{
public static void main(String ... arguments)
{
Main2 main2 = new Main2();
main2.createUI();
main2.setVisible(true);
}
public void createUI()
{
JPanel wingPanel = new JPanel();
FlowLayout flowLayout = new FlowLayout();
flowLayout.setHgap(35);
wingPanel.setLayout(flowLayout);
JButton btnone = new JButton("Lwing");
JButton btntwo = new JButton("center");
JButton btnthr = new JButton("Rwing");
wingPanel.add(btnone);
wingPanel.add(btntwo);
wingPanel.add(btnthr);
// -------------------------------------------
JButton mid1 = new JButton("mid1");
JButton mid2 = new JButton("mid2");
JButton mid3 = new JButton("mid3");
JButton mid4 = new JButton("mid4");
JPanel midfieldPanel = new JPanel();
GroupLayout groupLayout = new GroupLayout(midfieldPanel);
GroupLayout.SequentialGroup horizontalGroup = groupLayout.createSequentialGroup();
groupLayout.setHorizontalGroup(horizontalGroup);
horizontalGroup.addComponent(mid1);
horizontalGroup.addComponent(mid2);
horizontalGroup.addComponent(mid3);
horizontalGroup.addComponent(mid4);
GroupLayout.SequentialGroup verticalGroup = groupLayout.createSequentialGroup();
groupLayout.setVerticalGroup(verticalGroup);
GroupLayout.ParallelGroup midButtonGroup = groupLayout.createParallelGroup(GroupLayout.Alignment.CENTER);
midButtonGroup.addComponent(mid1);
midButtonGroup.addComponent(mid2);
midButtonGroup.addComponent(mid3);
midButtonGroup.addComponent(mid4);
verticalGroup.addGroup(midButtonGroup);
JPanel teamPanel = new JPanel();
BoxLayout boxLayout = new BoxLayout(teamPanel, BoxLayout.PAGE_AXIS);
teamPanel.setLayout(boxLayout);
teamPanel.add(wingPanel);
teamPanel.add(midfieldPanel);
JScrollPane scrollPane = new JScrollPane(teamPanel);
getContentPane().add(scrollPane);
pack();
}
}
EDIT: as requested, the below does the same thing with only GroupLayout.
There is no interaction between the two groups, because GroupLayout aligns things in columns, and your players are not in columns.
And yes, I suppose it is difficult -- GroupLayout, as I understand it, was really intended for use by GUI builder tools, not really for building UIs by hand. I personally have a supporter class or two that allows GroupLayout UIs to be built with slightly simpler logic. But in any event, I think you need to understand the building blocks:
GroupLayout allows - and requires - that you place each component in both horizontal and vertical row/column position independently; this is useful since so many UIs require rows and columns of mixed components and variable extra components.
A sequential group of components in dimension X is arranged sequentially in dimension X; a parallel group in dimension X is also arranged sequentially, but perpendicular to dimension X.
The layout maintains preferred sizes of components; row width and column height are set at the maximum preferred size of the constituent components.
The overall GroupLayout object has one vertical and one horizontal grouping; within that, sequential and parallel groups are created to create the overall layout desired.
I know the examples in the tutorial(s) I've read do not create separate variables to hold the internal sequential and parallel groups, preferring to use forms like new X().addComponent().addGroup() etc. But I think that makes it harder to understand what the code is actually doing, not easier; and the nested parentheses become their own maintenance problem. So I think this is a better way to do things, especially for those just getting started with this layout.
package grouplayout;
import java.awt.FlowLayout;
import javax.swing.BoxLayout;
import javax.swing.GroupLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
public class Main3 extends JFrame
{
public static void main(String ... arguments)
{
Main3 main2 = new Main3();
main2.createUI();
main2.setVisible(true);
}
public void createUI()
{
JButton btnone = new JButton("Lwing");
JButton btntwo = new JButton("center");
JButton btnthr = new JButton("Rwing");
JPanel wingPanel = new JPanel();
GroupLayout wingGroupLayout = new GroupLayout(wingPanel);
GroupLayout.SequentialGroup wingHorizontalGroup = wingGroupLayout.createSequentialGroup();
wingGroupLayout.setHorizontalGroup(wingHorizontalGroup);
wingHorizontalGroup.addComponent(btnone);
wingHorizontalGroup.addComponent(btntwo);
wingHorizontalGroup.addComponent(btnthr);
GroupLayout.SequentialGroup wingVerticalGroup = wingGroupLayout.createSequentialGroup();
wingGroupLayout.setVerticalGroup(wingVerticalGroup);
GroupLayout.ParallelGroup wingButtonGroup = wingGroupLayout.createParallelGroup();
wingButtonGroup.addComponent(btnone);
wingButtonGroup.addComponent(btntwo);
wingButtonGroup.addComponent(btnthr);
wingVerticalGroup.addGroup(wingButtonGroup);
// -------------------------------------------
JButton mid1 = new JButton("mid1");
JButton mid2 = new JButton("mid2");
JButton mid3 = new JButton("mid3");
JButton mid4 = new JButton("mid4");
JPanel midfieldPanel = new JPanel();
GroupLayout groupLayout = new GroupLayout(midfieldPanel);
GroupLayout.SequentialGroup horizontalGroup = groupLayout.createSequentialGroup();
groupLayout.setHorizontalGroup(horizontalGroup);
horizontalGroup.addComponent(mid1);
horizontalGroup.addComponent(mid2);
horizontalGroup.addComponent(mid3);
horizontalGroup.addComponent(mid4);
GroupLayout.SequentialGroup verticalGroup = groupLayout.createSequentialGroup();
groupLayout.setVerticalGroup(verticalGroup);
GroupLayout.ParallelGroup midButtonGroup = groupLayout.createParallelGroup(GroupLayout.Alignment.CENTER);
midButtonGroup.addComponent(mid1);
midButtonGroup.addComponent(mid2);
midButtonGroup.addComponent(mid3);
midButtonGroup.addComponent(mid4);
verticalGroup.addGroup(midButtonGroup);
JPanel teamPanel = new JPanel();
BoxLayout boxLayout = new BoxLayout(teamPanel, BoxLayout.PAGE_AXIS);
teamPanel.setLayout(boxLayout);
teamPanel.add(wingPanel);
teamPanel.add(midfieldPanel);
JScrollPane scrollPane = new JScrollPane(teamPanel);
getContentPane().add(scrollPane);
pack();
}
}
