How to show tooltip description in Android Studio?

For Android Studio 3.6.3 IDE installed on macOS, enable tool tips by:

Preferences > Editor > General > Code Completion > Show the documentation popup in 0 ms

You can use Ctrl + Q to show the quick javadoc of current caret location.

If you want it on hover go to

File > Settings > Editor

and tick the checkbox "Show quick doc on mouse move". You can also set the time delay after hover to make sure just moving cursor in editor doesn't show the javadocs.

EDIT :

As per comments

Alt + Enter can be used for Quick Fixes in Android Studio, It will give you drop down for possible fixes same like in Eclipse.

The strange thing about Android Studio and tool tips is that Android doesn't call them tool tips. Instead "quick documentation on mouse move." Oh my.

Anyways, for Android Studio 2.1.2 IDE installed on Mac OS X, enable tool tips by:
-"Android Studio" menu
-"Preferences..." menu item
-open "Editor" twirl
-Click on the "General" twirl, not to be confused with twirling open the "General" twirl (this kind of stuff is bad UX design).
-"Other" section
-third field down in the section which is a checkbox labeled "Show quick documentation on mouse move."

Oh BTW, this setting is disabled by default which is very strange.