[Java] Class Hierarchy Design - Serious Help Needed!

Its a basic parsing problem. What you need is a tokenizer to break the string into "tokens", a parser to parse the string for correct syntax and objects creation. The class hierachy should be something like this:

basic
class Char
class Int
class Float

expressions
class Add
class Divide
class Bracket

As you can see, Add and Divide take in 2 arguments, Bracket takes 1, etc. The rest you should learn for yourself.