JavaApplication

package <package>;
 
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class MainFrame extends JFrame {
 
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
 
	public MainFrame() {
 
		// Beliebiger Inhalt
 
		addWindowListener(new WindowAdapter() {
			public void windowClosing(WindowEvent we) {
				System.exit(0);
			}
		});
	}
 
	public static void main(String[] args) {
		MainFrame frame = new MainFrame();
 
		// JFrame soll 400px * 300 px groß sein
		Dimension frameSize = new Dimension(400, 300);
 
		// Größe des Bildschirms ermitteln
		Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
 
		// Position des JFrames errechnen
		int top = (screenSize.height - frameSize.height) / 2;
		int left = (screenSize.width - frameSize.width) / 2;
 
		// Größe zuordnen
		frame.setSize(frameSize);
 
		// Position zuordnen
		frame.setLocation(left, top);
 
		// Anzeigen
		frame.setVisible(true);
	}
}