Re: Simple BorderLayout problem

From:

Knute Johnson <nospam@rabbitbrush.frazmtn.com>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 15 Feb 2010 09:28:35 -0800

Message-ID:

<7vfen.90341$BV.50820@newsfe07.iad>

On 2/15/2010 8:50 AM, Fencer wrote:

Hello, I have a problem with BorderLayout, and I bet it's really simple.
I have JPanel with a TitledBorder (like a "group" widget) and this
JPanel contains a button.

Now I want to displays this JPanel centered horizontally and vertically
and I don't want it to occupy all the space of the client area of the
JFrame.

I tried this:
package main;

import java.awt.BorderLayout;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.TitledBorder;

public class CenteredGroup {

CenteredGroup() {
frame.setSize(1024, 768);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JPanel contentPane = (JPanel)frame.getContentPane();

BorderLayout borderLayout = new BorderLayout(50, 50);

frame.setLayout(borderLayout);

contentPane.setLayout(borderLayout);

There is no need to set both the JFrame layout and the ContentPane layout.

JPanel groupPanel = new JPanel();

groupPanel.setBorder(new TitledBorder("This is my group text."));

JButton button = new JButton("A button");

groupPanel.add(button);

contentPane.add(groupPanel, BorderLayout.CENTER);

frame.setVisible(true);
}

public static void main(String[] args) {
new CenteredGroup();
}

JFrame frame = new JFrame("Centered Group");
}

A little indentation would be nice.

However, the "group control" occupies the entire client area of the
frame. Why?

I can provide a screenshot of what it looks like and how I want it to
look like if you have trouble understanding my problem description.

- F

BorderLayout causes the components added to it to fill the available
area. Specifying the hgap and vgap just put extra space between
components not the outer edges. Use a layout that will not do that such
as GridBagLayout. GBL also has the ability to adjust the size and
positions of components.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class test8 extends JPanel {
     public test8() {
         setPreferredSize(new Dimension(40,30));
         setBackground(Color.BLUE);
     }

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 JFrame f = new JFrame();
                 f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                 f.setLayout(new GridBagLayout());
                 test8 t8 = new test8();
                 f.add(t8);
                 f.setSize(400,300);
                 f.setVisible(true);
             }
         });
     }
}

And this one is a button centered in a JPanel, centered in the JFrame.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class test9 extends JPanel {
     public test9() {
         super(new GridBagLayout());
         setPreferredSize(new Dimension(160,120));
         JButton b = new JButton("Press Me");
         add(b);
         setBorder(BorderFactory.createLineBorder(Color.BLUE,10));
     }

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 JFrame f = new JFrame();
                 f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                 f.setLayout(new GridBagLayout());
                 test9 t9 = new test9();
                 f.add(t9);
                 f.setSize(800,600);
                 f.setVisible(true);
             }
         });
     }
}

It is trivial with GBL to align the JPanel to the upper left corner of
the JFrame.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class test9 extends JPanel {
     public test9() {
         super(new GridBagLayout());
         setPreferredSize(new Dimension(160,120));
         JButton b = new JButton("Press Me");
         add(b);
         setBorder(BorderFactory.createLineBorder(Color.BLUE,10));
     }

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 JFrame f = new JFrame();
                 f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                 f.setLayout(new GridBagLayout());

                 GridBagConstraints c = new GridBagConstraints();
                 c.anchor = GridBagConstraints.NORTHWEST;
                 c.weightx = c.weighty = 1.0;

                 test9 t9 = new test9();
                 f.add(t9,c);
                 f.setSize(800,600);
                 f.setVisible(true);
             }
         });
     }
}

--

Knute Johnson
email s/nospam/knute2010/