I am thinking that you want to call a jinternal frame from the jframe main window. try this code
public void actionPerformed (ActionEvent ae)
{
Object obj = ae.getSource();
if (obj == newBook || obj == book || obj == btnNewBook) {
boolean b = openChildWindow ("Add New Book");
if (b == false) {
AddBook adBook = new AddBook (con);
desktop.add (adBook);//Adding Child Window to DesktopPane.
adBook.show (); //Showing the Child Window.
}
}