Centering Java Windows & Dialogs

Centering Windows:
Thought I would share a quick little trick for those who haven't already found this out. Many times when you display an Application window or Dialog box you want it to appear centered either onscreen or centered within another window or component. Instead of figuring out the absolute position of the window or dialog on screen there is a much easier solution.

JFrame mainFrame = new JFrame("Test Center On Screen");
//must have this in order to porperly exit application when window closes
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

//size must be set prior to setting location.
mainFrame.setSize(600, 400);

//this is on way to center the frame
mainFrame.setLocationRelativeTo(null);

//show the window.
mainFrame.setVisible(true);

Alternatives to setting the size with absolute values is using the pack(); function which will use the preffered size and layout managers to determine the window size.

Another way to center the frame is by calling the same setLocationRelativeTo(); function as follows.

//same as above
mainFrame.setLocationRelativeTo(mainFrame);

There is no advantage to using either method, as far as I know, so it's whichever you believe makes the most sense to read.

Centering Dialogs:
Similarily you can center Dialogs or even Windows on any component. This is useful for modal dialogs that need to be closed before the user can continue working in the main application.

   //create a new modal dialog
   JDialog dlg = new JDialog(mainFrame, true);
   
   //simply dispose of the dialog
   dlg.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
   
   //set the size prior to setting location
   dlg.setSize(300, 200);
   
   //center the dialog in the application window
   dlg.setLocationRelativeTo(mainFrame);
   
   //display the modal dialog
   dlg.setVisible(true);

So as you can see it's quite simple to center windows and dialogs in Java. You can also center a Dialog or Window to any Component using the same setLocationRelativeTo function thus when setVisible(true); is called the Window will appear centered over that component on screen.

It's Been a while!

It's been a while since I have had time to post, and pretty much a general lack of interesting things to post. But I just thought I would post something and try to get back into the blogsphere, even though I was never really in it from the beginning.

I am still working hard on Java Game Programming. My most recent project is a Game Editor Tool for the purpose of creating games without needing to be a programmer. Hopefully I can get some screens out soon.

I also have many ideas for new posts here, they may be a bit longer than pervious ones and contain more complex code. I've wanted to handle a couple topics that are needed for creating games for a long time now. Some upcoming posts will include:

• Abstract Collision Detection: Using Visitor Pattern
• Particle Systems: Using the Flyweight Pattern

Eventually I hope to make a post on how to bring all the snippets I have posted together to make games. Any feedback as to your specific needs will help tremendously!

Thanks for reading!