How can I make it so that when a file type is selected in the JFileChooser window, an extension is added to the file name?

Question

Java

Hello. I would like to make it so that when the file type changes, its name changes: the extension is added to the name.

Threat As a last resort, you can make it so that after selecting a file, an extension is added to its name, depending on the selected file type, but so far I have not figured out how to get the extension using the selected filter.