Evaluate.java

import java.util.Scanner;

public class Evaluate{
    public static void main(String[] args){
        String[] samples = new String[]{
            " 5 + 6 * 7 /2",
            "5/2",
            "500/(3+2)",
            "5^2/4"
        };

        Evaluate e = new Evaluate();

        for(String s: samples){
            e.run(s);
        }
    }

    public float run(String input){
        System.out.println("--- " + input + " -> " + normalize(input) + " ---");
        Scanner s = new Scanner(normalize(input));

        while(s.hasNext()){
            System.out.println(s.next());
        }

        return 0.0f;
    }

    private String normalize(String input){
        return input.replaceAll("\\s*([()+\\*/^-])\\s*", " $1 ");
    }
}