Write a piece of code that prints out itself

Question

I'm new to this site, so I don't know whether this challenge already appeared:

Write a piece of source code, so that after running the code, it prints out exactly (i.e. not longer, not shorter) the source code itself.

The code can be in any programming language, but preferably in commonly used ones, such as the C family, Java, Python, Haskell, Ruby...