A DESCRIPTION OF THE REQUEST :
In JDialog class, there is no method to enable or disable the close (X) button. Even SetDefaultCloseOperation method can provide the user to do nothing on close or dispose on close but this will not stop windowClosing event to stop executing.
There is a requirement where close button should be disaplayed or not and also require to change the enable or disable (grayed color).

JUSTIFICATION :
Most of the time JDialog also be used to display the status of the operation going on. If user clicks on close button then depending upon its defaultCloseOperation it will perform that operation. But the requirement may be after completion of the process the dialog box should be closed by pressing (X) button as this will not happen if we put default close operation is DO Nothing. So using this enhancement one can simply enable the close button once the process is completed and close button is disabled while process is running.
Even the JInternalFrame supports visibility of close button by the method call this feature but JDialog is most fisible to have this one.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
On JDialog box the close(x) can be enabled or disabled(grayed).
Should have chance to setVisbility or similar like isClosable() method of JInternalFrame.
ACTUAL -
No method to eanble or disable the Cross or Close button.
isClosable() method is not available which is already there in JInternalFrame.