Full restart restarts the iOS, Android, or web app.
This takes longer because it also recompiles the
Java / Kotlin / ObjC / Swift code. On the web,
it also restarts the Dart Development Compiler.
There is no specific keyboard shortcut for this;
you need to stop and start the run configuration.

Flutter web currently supports hot restart but not
  hot reload.

Controls for run, run debug, hot reload, and hot restart in Android Studio

A code change has a visible effect only if the modified
Dart code is run again after the change. Specifically,
a hot reload causes all the existing widgets to rebuild.
Only code involved in the rebuilding of the widgets
is automatically re-executed. The main() and initState()
functions, for example, are not run again.

Special cases