IntelliJ allows the user to toggle the case of text selection to upper/lowercase with a single action called Toggle Case.

Once you select text & apply this action via shortcut, it converts the selection to uppercase by default, if you press the shortcut it again, the selected text would be converted to lowercase.

Currently uppercase & lowercase are implemented as separate actions.

It would be good to have a Toggle case action so that user need to remember just one shortcut instead of two different shortcuts to toggle case

Reference:
#3776