First, be aware that some users on some platforms would rather that you didn’t do this, as they have existing “placement” schemes. However, at least on MS-Windows, this technique is useful.
Subtract the width and height of the window from the width and height of the screen, divide by two, and go there.
The code for this is pretty simple. The part that might take a while
to figure out is the Dimension
of the screen.
There is a method getScreenSize( )
in the Toolkit
class, and a static method getDefaultToolkit( )
.
(The Toolkit
class relates to the underlying windowing toolkit; there are several
subclasses of it, one for X Windows on Unix, another for Macintosh,
etc.) Put these together and you have the
Dimension
you need.
Centering a Window
is such a common need that I
have packaged it in its own little class
UtilGUI
,
just as I did for the WindowCloser
class in Recipe 13.6. Here is the complete source for
UtilGUI
, which I’ll use without comment from
now on:
package com.darwinsys.util; import java.awt.*; /** Utilities for GUI work. */ public class UtilGUI { /** Centre a Window, Frame, JFrame, Dialog, etc. */ public static void centre(Window w) { // After packing a Frame or Dialog, centre it on the screen. Dimension us = w.getSize( ), them = Toolkit.getDefaultToolkit().getScreenSize( ); int newX = (them.width - us.width) / 2; int newY = (them.height- us.height)/ 2; w.setLocation(newX, newY); } /** Center a Window, Frame, JFrame, Dialog, etc., * but do it the American Spelling Way :-) */ public static void center(Window w) { UtilGUI.centre(w); } }
To use it after the relevant import, you can simply say, for example:
myFrame.pack( ); UtilGUI.centre(myFrame); myFrame.setVisible(true);
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