A couple of things...
I think you are starting off by making this too hard. For example:
"Assume the variables have been declared and fullName already initialized."
So why are you creating a scanner to read the full name in? The above directions to me mean you can simply do this:
you don't need to worry about HOW it got that way, so you can get it that way however you want.
So now you have fullName populated. How would you split it? Generally, people here would tell you to
StopCoding (<---that's a link. Click it). The main thing a programmer does is NOT write code, but instead THINKS about the problem. Solve it with paper and pencils. Literally write out the directions you would hand someone else if you wanted them to do it.
Writing a single line of code before you know what you are going to write is a BAD idea.