How to change JFrame to JDialog?

Question

Java

There is a main window from it I launch child.
It was required to make child modal.
I changed JFrame to JDialog, it became modal, but stopped drawing its components, that is, it became an empty window.
What should be done to make the window modal and show its components?

Answer 1

I removed the panel from the dialog, and everything worked.
Can't a JDialog contain a JPanel?