How do I center a JDialog on screen?

Question

How do I go about positioning a JDialog at the center of the screen?

johnstok · Accepted Answer · 2008-10-17T18:35:36.730

167

In Java 1.4+ you can do:

final JDialog d = new JDialog();
d.setSize(200,200);
d.setLocationRelativeTo(null);
d.setVisible(true);

Or perhaps (pre 1.4):

final JDialog d = new JDialog();
d.setSize(200, 200);
final Toolkit toolkit = Toolkit.getDefaultToolkit();
final Dimension screenSize = toolkit.getScreenSize();
final int x = (screenSize.width - d.getWidth()) / 2;
final int y = (screenSize.height - d.getHeight()) / 2;
d.setLocation(x, y);
d.setVisible(true);

edited Oct 17 '08 at 18:35

answered Oct 17 '08 at 18:27

johnstok

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7

what exactly is happening when you setlocation relative to null? – Mark Norgren Aug 19 '09 at 13:30
6

Wanted to add that you do need to use setSize() or else the setLocationRelativeTo() will not work. I had to use both setSize() AND setPreferredSize() in order to get everything to look right. – Richard Jun 16 '11 at 13:35
2

In answer to the question by @marked: If the component is not currently showing, or c is null, the window is placed at the center of the screen. (from the java.awt.Window javadocs) – Jeremy Brooks Feb 21 '12 at 21:14
2

Note that both of these methods will center the dialog *on the primary monitor* (at least on Windows). Better to pass an argument to `setLocationRelativeTo` so the dialog appears on the appropriate monitor for multi-monitor users. – Brad Mace Aug 28 '14 at 13:04
5

I had to call `pack()` before `setLocationRelativeTo(null)` to properly center the dialog. – Matthias Braun Nov 30 '15 at 10:35
1

This solution still works with Java 8! To actually position it in the center, the order has to be: 1. `pack()`, 2. `setLocationRelativeTo(this)`, 3. `setVisible(true)`. Any other order and the dialog won't be centered but in the top left corner! – Neph Sep 12 '19 at 09:55
This helps for putting a `JDialog` that contains an instance of `JOptionPane` in the center. – Tech Expert Wizard Nov 19 '20 at 15:25
When you call dialog.setLocationRelativeTo(null) statement before dialog.setSize(...) , dialog doesn't appear at the center of the screen. – Pekmezli Dürüm Feb 19 '23 at 14:56

score 11 · Answer 2 · edited Apr 10 '13 at 13:25

11

Use this line after the pack() method:

setLocation((Toolkit.getDefaultToolkit().getScreenSize().width)/2 - getWidth()/2, (Toolkit.getDefaultToolkit().getScreenSize().height)/2 - getHeight()/2);

edited Apr 10 '13 at 13:25

Corey Adler

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answered Apr 10 '13 at 13:06

Kunax

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This is too complicated. It requires manual positioning of the dialog to the center according to the dialog's size and the screen size. – Tech Expert Wizard Nov 19 '20 at 15:27

score 8 · Answer 3 · answered Mar 06 '12 at 04:30

Two helpers for centering within the screen or within the parent.

// Center on screen ( absolute true/false (exact center or 25% upper left) )
public void centerOnScreen(final Component c, final boolean absolute) {
    final int width = c.getWidth();
    final int height = c.getHeight();
    final Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    int x = (screenSize.width / 2) - (width / 2);
    int y = (screenSize.height / 2) - (height / 2);
    if (!absolute) {
        x /= 2;
        y /= 2;
    }
    c.setLocation(x, y);
}

// Center on parent ( absolute true/false (exact center or 25% upper left) )
public void centerOnParent(final Window child, final boolean absolute) {
    child.pack();
    boolean useChildsOwner = child.getOwner() != null ? ((child.getOwner() instanceof JFrame) || (child.getOwner() instanceof JDialog)) : false;
    final Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    final Dimension parentSize = useChildsOwner ? child.getOwner().getSize() : screenSize ;
    final Point parentLocationOnScreen = useChildsOwner ? child.getOwner().getLocationOnScreen() : new Point(0,0) ;
    final Dimension childSize = child.getSize();
    childSize.width = Math.min(childSize.width, screenSize.width);
    childSize.height = Math.min(childSize.height, screenSize.height);
    child.setSize(childSize);        
    int x;
    int y;
    if ((child.getOwner() != null) && child.getOwner().isShowing()) {
        x = (parentSize.width - childSize.width) / 2;
        y = (parentSize.height - childSize.height) / 2;
        x += parentLocationOnScreen.x;
        y += parentLocationOnScreen.y;
    } else {
        x = (screenSize.width - childSize.width) / 2;
        y = (screenSize.height - childSize.height) / 2;
    }
    if (!absolute) {
        x /= 2;
        y /= 2;
    }
    child.setLocation(x, y);
}

score 5 · Answer 4 · 2009-02-25T23:09:57.163

here's my solution to retrieve screen dimension with multiple monitors.

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

/**
 * Méthodes statiques pour récupérer les informations d'un écran.
 *
 * @author Jean-Claude Stritt
 * @version 1.0 / 24.2.2009
 */
public class ScreenInfo {

  /**
   * Permet de récupérer le numéro de l'écran par rapport à la fenêtre affichée.
   * @return le numéro 1, 2, ... (ID) de l'écran
   */
  public static int getScreenID( JFrame jf ) {
    int scrID = 1;
    GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
    GraphicsDevice[] gd = ge.getScreenDevices();
    for (int i = 0; i < gd.length; i++) {
      GraphicsConfiguration gc = gd[i].getDefaultConfiguration();
      Rectangle r = gc.getBounds();
      if (r.contains(jf.getLocation())) {
        scrID = i+1;
      }
    }
    return scrID;
  }

  /**
   * Permet de récupérer la dimension (largeur, hauteur) en px d'un écran spécifié.
   * @param scrID --> le n° d'écran
   * @return la dimension (largeur, hauteur) en pixels de l'écran spécifié
   */
  public static Dimension getScreenDimension( int scrID ) {
    Dimension d = new Dimension(0, 0);
    if (scrID > 0) {
      GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
      DisplayMode mode = ge.getScreenDevices()[scrID - 1].getDisplayMode();
      d.setSize(mode.getWidth(), mode.getHeight());
    }
    return d;
  }

  /**
   * Permet de récupérer la largeur en pixels d'un écran spécifié.
   * @param scrID --> le n° d'écran
   * @return la largeur en px de l'écran spécifié
   */
  public static int getScreenWidth( int scrID ) {
    Dimension d = getScreenDimension(scrID);
    return d.width;
  }

  /**
   * Permet de récupérer la hauteur en pixels d'un écran spécifié.
   * @param scrID --> le n° d'écran
   * @return la hauteur en px de l'écran spécifié
   */
  public static int getScreenHeight( int scrID ) {
    Dimension d = getScreenDimension(scrID);
    return d.height;
  }

}

score 3 · Answer 5 · answered Oct 18 '08 at 22:02

3

AFAIK you can pass a GraphicEnvironment to each JDialog/JFrame/JWindow constructor. This object describes the monitor to use.

answered Oct 18 '08 at 22:02

ZeissS

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How do I center a JDialog on screen?

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