How can I use internal frames with buttons to call others internal frames?

Question

Hello.
I'm building a MDI-application using JFrames and several JInternalFrames, but I have problems.
A JFrame has JMenuBar with JMenu and JMenuItem. One of these, call the first JInternal that has its interface. In this interface has a button that call other type (a class extension of JInternalFrame) JInternalFrame.
When I clicked button happen a exception (java.lang.NullPointer).
What happening?
Help me, please.

Answer 1

What i usually do is to give my desktop to my internal frames. So within the internalframe, you can use your desktop and add other internal frames to it.
The code should look something like the following.
desktop = your JDesktopPane
MyInternalFrame = an InternalFrame
AnotherMyInternalFrame = another InternalFrame
public class MyInternalFrame extends JInternalFrame implements ActionListener
  private JButton jb = new JButton("Launch");
  private JLayeredPane desktop = null;
  public MyInternalFrame(JLayeredPane desktop)
    this.desktop = desktop;
    getContentPane().add(jb);
    jb.addActionListener(this);
  public void actionPerformed(ActionEvent ae)
    if (ae.getSource() == jb)
      desktop.add(new AnotherMyInternalFrame(desktop),JLayeredPane.DEFAULT_LAYER);
}