Hi jade, and welcome to JavaRanch!
It would be really helpful if you could give us an idea of what you've tried so far and where you're stuck.
My advice for now would be to forget about the input business.
Just write a program that uses a hard-coded set of numbers and write the logic to determine the highest and lowest value.
You could tie that logic to dynamic input at a later stage.
Edit: Ugh, too slow (again)
Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life.