import java.awt.Dimension;
import java.awt.Toolkit;
import javax.swing.JFrame;
public class Main {
public static void main(String[] argv) throws Exception {
Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
JFrame window = new JFrame();
window.setSize(300,300);
int w = window.getSize().width;
int h = window.getSize().height;
int x = (dim.width - w) / 2;
int y = (dim.height - h) / 2;
window.setLocation(x, y);
window.setVisible(true);
}
}