java make a popup

1import java.awt.Dimension;
2import javax.swing.JFrame;
3import javax.swing.SwingUtilities;
4
5public class JFrameSize
6{
7
8  public static void main(String[] args)
9  {
10    // schedule this for the event dispatch thread (edt)
11    SwingUtilities.invokeLater(new Runnable()
12    {
13      public void run()
14      {
15        displayJFrame();
16      }
17    });
18  }
19
20  static void displayJFrame()
21  {
22    // create our jframe as usual
23    JFrame jframe = new JFrame("JFrame Size Example");
24    jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
25
26    // set the jframe size and location, and make it visible
27    jframe.setPreferredSize(new Dimension(400, 300));
28    jframe.pack();
29    jframe.setLocationRelativeTo(null);
30    jframe.setVisible(true);
31  }
32
33}
34