import java.awt.Dimension;
import java.awt.GraphicsEnvironment;
import java.awt.Point;
import javax.swing.JFrame;
public class Main extends JFrame {
public Main() {
setSize(250, 200);
centerFrame();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
private void centerFrame() {
Dimension windowSize = getSize();
GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
Point centerPoint = ge.getCenterPoint();
int dx = centerPoint.x - windowSize.width / 2;
int dy = centerPoint.y - windowSize.height / 2;
setLocation(dx, dy);
}
public static void main(String[] args) {
Main ex = new Main();
ex.setVisible(true);
}
}