How to duplicate a whole line in Vim?

Question

How do I duplicate a whole line in Vim in a similar way to Ctrl+D in IntelliJ IDEA/ Resharper or Ctrl+Alt+&

Answer 1

For those starting to learn vi, here is a good introduction to vi by listing side by side vi commands to typical Windows GUI Editor cursor movement and shortcut keys. It lists all the basic commands including yy (copy line) and p (paste after) or P(paste before).

vi (Vim) for Windows Users