Beginners Java calculator
I'm learning Java too!

Looking at this the only thing I might suggest is that you only do the calculations that you need to. You could then remove all answer variables and print the result of the calculations directly, saving time and memory, albeit not much.

In terms of presentation, I personally would use lowerCamelCase for variable naming, e.g. firstNum, and I would also indent all of the cases as they are within the switch block. Finally, for input. nextDouble(); I'd make sure there was no space there.

Despite what I say for the presentation, that part of it is totally up to you, so do what you prefer, as long as it looks clear!