Modifier Modifier Plugin for IntelliJ IDEA is a plugin which provides hotkey bindings for inserting and removing Java modifiers like synchronized, final, and public/protected/default/private.
abstract for current method or classprivate/package-private/protected/public for current field, method, constructor, or class (only package-private and public are cycled for non-inner classes)final for current parameter, variable, field, method, or classstatic for current field, method, or inner classstrictfp for current method or classsynchronized for current methodtransient for current fieldvolatile for current fieldYou can download and install the plugin through the IDEA Plugins Settings.
You can download the source code.