Exception : adding a window to a container. How to solve it?

Question

I have a JDialog class named Preferences. This class creates a constructor like:

class Preferences extends javax.swing.JDialog {
          Preferences(java.awt.Frame parent,modal)  {
                      super(parent,modal);
                      //......
          }
}

In my program I want this preferences dialog to open up as I click a button from a JFrame form. After I registered the action listener on the button, I wrote the code inside as:

Frame fr = new Frame();
Preferences p = new Preferences(fr,false);
fr.add(p);
fr.setVisible(true);

When I run this code I get the following exception (as I click the button):

Exception in thread "AWT-EventQueue-0" 
    java.lang.IllegalArgumentException: adding a window to a container

What does this mean and how can I solve it?

Answer 1

What does this mean..

One top level container (dialog) cannot be added to another (frame).

..and how can i solve this ?

Just call setVisible(true) on the Preferences dialog, rather than adding it.