The simplest way would be to use the
Collections#shuffle(List<?> list) method which delivers decent performance and output.
If you have an assignment to create such a shuffling algorithm, then look at the source code of the Collections class for hints.
The romantic image of an über-programmer is someone who fires up Emacs, types like a machine gun, and delivers a flawless final product from scratch. A more accurate image would be someone who stares quietly into space for a few minutes and then says “Hmm. I think I’ve seen something like this before.” - John D