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

问题

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?

回答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.

回答2:

You don't add the JDialog to the JFrame, that makes no sense whatsoever since the add(...) method is for adding components to be displayed in the container, not by the container. You display the JDialog from the JFrame's JButton's ActionListener. You also shouldn't be mixing AWT (Frame) components and Swing components together for no good reason.

Your question suggests that you would benefit greatly by going through the Swing tutorials.