How can I enter an equation using the keyboard?

Question

Java

There is a program that calculates the minimum of a function by enumeration. The function is defined statically in the program code. How can I make the user enter a function from the keyboard in the format, for example: x + 5? For every time I'm tired of editing the source code. So that after entering from the keyboard, this function is passed to the method and then processed.

private double function(double x){
    return x*Math.exp(x)+Math.pow(x,2);
    }

Answer 1

Google about Polish notation

Answer 2

Java? binshel !