JDialog popup too small

Question

Every time I run this piece of code, the output is a dialog box that appears at the top left hand corner of the screen and the title does not show.

Is there any way that I can change this so that the dialog appears at the middle and of acceptable size?

Code:

public class Test {

public static void main(String[] args) {

    JFrame f = new JFrame();

    final JDialog dialog = new JDialog(f, "Hello world", true);
    Timer timer = new Timer(10000, new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            dialog.setVisible(false);
            dialog.dispose();
        }
    });
    timer.setRepeats(false);
    timer.start();

    dialog.setVisible(true); 
    System.out.println("Dialog closed");

}
}

Answer 1

Absolutely. By default, a JDialog (or a JFrame) will appear like that. You need to set bounds on it:

dialog.setBounds(xPosition, yPosition, width, height);

However, if you just set some magic numbers for it, this will not scale well to other systems. Instead, get the screen dimension, and set off of that:

//static and final because no reason not to be. Insert this at the class definition
static final Dimension SCREEN_DIMENSION = Toolkit.getDefaultToolkit().getScreenSize();
...
//I'd also make this static and final and insert them at the class definition
int dialogWidth = SCREEN_DIMENSION.width / 4; //example; a quarter of the screen size
int dialogHeight = SCREEN_DIMENSION.height / 4; //example
...
int dialogX = SCREEN_DIMENSION.width / 2 - dialogWidth / 2; //position right in the middle of the screen
int dialogY = SCREEN_DIMESNION.height / 2 - dialogHeight / 2;

dialog.setBounds(dialogX, dialogY, dialogWidth, dialogHeight);

Alternatively, if you add components to the JDialog, then call

dialog.pack();

the dialog will now be the minimum size to accommodate the components. If you are using components that should be packed tight, use this method; then you don't have to painstakingly construct the right width and height by hand.

Answer 2

"Is there any way that I can change this so that the dialog appears at the middle and of acceptable size?"

If you just add components to it, pack it, and set it location relative to null, it should work fine

It is preferred to .pack() instead of setting a size. For pack to work, you need to actually add components. the .pack() will do exactly as it's name suggest - pack the frame with respecting all the added components' preferred sizes.

Also with setLocationRelativeTo() you set the dialog loation relative to a component. If you use null, it will be centered on the screen always. But if you set the location relative to its parent, the frame, it will appear centered over the frame.

I have absolutely no idea what you're trying to achieve with the timer, so I just prefer to no-comment

See example

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.Timer;

public class Test {

    public static void main(String[] args) {

        JFrame f = new JFrame();
        final MyDialog dialog = new MyDialog(f, "Title", true);
        Timer timer = new Timer(10000, new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                dialog.setVisible(false);
                dialog.dispose();
            }
        });
        timer.setRepeats(false);
        timer.start();

        dialog.setVisible(true);
        System.out.println("Dialog closed");

    }

    private static class MyDialog extends JDialog {

        public MyDialog(JFrame frame, String title, boolean modal) {
            super(frame, title, modal);

            setLayout(new BorderLayout());
            add(new JButton("NORTH"), BorderLayout.NORTH);
            add(new JButton("SOUTH"), BorderLayout.SOUTH);
            add(new JButton("EAST"), BorderLayout.EAST);
            add(new JButton("WEST"), BorderLayout.WEST);
            add(new JButton("CENTER"), BorderLayout.CENTER);

            pack();
            setLocationRelativeTo(null);

        }
    }
}

---

As a side note, you should be running Swing apps from the Event Dispatch Thread (EDT) like this

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable(){
        public void run() {
           //  the code from your main method here
        }
    });
}

Answer 3

Add these lines of code between timer.start(); and dialog.setVisible(true); statements -

   timer.start();

   dialog.setPreferredSize(new Dimension(50, 150));//set your desired size
   dialog.pack();
   Toolkit toolkit = Toolkit.getDefaultToolkit();
   Dimension screenSize = toolkit.getScreenSize();
   int iWidth = (screenSize.width - dialog.getWidth()) / 2;
   int iHeight = (screenSize.height - dialog.getHeight()) / 2;
   dialog.setLocation(iWidth, iHeight);

   dialog.setVisible(true);

This code will set the dialog to center of your screen.

Answer 4

Add this line

dialog.setBounds(0, 0, 1000, 500);