How to show access modifiers for classes in IntelliJ IDEA?

UPDATE

Since 2019.2 version you can enable it in the Project view options, toggle the Show Visibility Icons:

Show Visibility Icons


For older versions:

This option was disabled intentionally, see this comment for the explanation:

This information was intentionally removed, as we believe that it brings more clutter than actual value.

To enable it back add -Dide.projectView.show.visibility=true in Help | Edit Custom VM Options.


Since 2019.2 there is actually an easy to use option as described in comment:

you can find this setting in options menu of Project Tool Window. It's called "Show Visibility Icons"