In java there's no straight forward property to get displayed your FORM on the center of the screen.
Here's a method to do so...
First you have to import two packages ....
Next go to the design view of your form & click on the form. In the properties of the form see what's the prefferedSize is.
say, prefferedSize = [426,473]
here 426 is the width of your form, & 473 is the length of the form.
Next initiate following variables,
Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();
//this will get screen dimensions
int X = (screen.width / 2) - (426 / 2); // Center horizontally.
int Y = (screen.height / 2) - (700/ 2); // Center vertically.
here 426 is the width of your form & 700 is a value which makes your form vertically centered.
But you can change this 700 according to the vertical position you want.
Next again go to the properties of your form & go to bounds.
There select Custom Code & enter the following line.
here 426 is the width & 473 is the length of your form.
Then press ok & check again whether the code line you entered is there.
Now run your form & see.