Of course you know how to start!

You make a class called AlphabetMonster, and you give it main() method.

Then you ask the user for input, and read that input. If your Scanner is called 'monster', then you read it like this:

char food = monster.next().charAt(0);

And now you need to ***select*** a response based on what the user entered as 'food'. Is the food an upper case letter? A lower case letter? A digit? The Character class has methods to help you check that -- they are listed in the textbook in Chaper 4, and on the lecture slides...