nsIWebBrowserPrint related

I have embedded mozilla in my Java application.Iam trying to us
printPreview to get number of pages.But getPrintPreviewNumPages() is
not working


Am I missing some step here.Please help.Iam stuck.

=============================
nsIInterfaceRequestor ir = (nsIInterfaceRequestor)
domwindow.queryInterface(nsIInterfaceRequestor.NS_IINTERFACEREQUESTOR_IID);

nsIWebBrowserPrint print = (nsIWebBrowserPrint)
ir.getInterface(nsIWebBrowserPrint.NS_IWEBBROWSERPRINT_IID);

 nsIPrintSettings settings=print.getGlobalPrintSettings();
 settings.setOrientation(nsIPrintSettings.kPortraitOrientation);
 settings.setPaperSize(nsIPrintSettings.kPaperSizeDefined);
 settings.setShrinkToFit(true);
 settings.setPrintReversed(false);
 settings.setPrintSilent(true);
 settings.setIsInitializedFromPrefs(true);

 print.printPreview(settings,null,null);

     	 try
	 {
		Thread.sleep(1000);
	 }catch(Exception e){}

  System.out.println("preview child dom window
"+print.getPrintPreviewNumPages());

regards,
Krith