Reverse Polish Notation Stack Driver Demo V2

// A.C. Silvestri
// 10/16/17
// CSC-220 Data Structures
// Reverse Polish Notation Stack Driver Demo V2
// Supports negative numbers

package chapter10.Stacks;

import java.util.Scanner;

public class RPN {
    public static void main(String[] args) {

        StackOfIntegers0 stack = new StackOfIntegers0();
        Scanner input = new Scanner(System.in);
        while (input.hasNextLine()) {
            String line = input.nextLine();
            String tokens[] = line.split("\\s+");
            for (int i = 0; i < tokens.length; i++) {
                char ch = tokens[i].charAt(0);
                if (Character.isDigit(ch)) {
                    stack.push(Integer.parseInt(tokens[i]));
                }
                else if (ch == '+')
                    if (tokens[i].length() == 1) {
                        int a = stack.pop();
                        int b = stack.pop();
                        stack.push(b + a);
                    }
                    else {
                        stack.push(Integer.parseInt(tokens[i]));
                    }
                else if (ch == '-')
                    if (tokens[i].length() == 1) {
                        int a = stack.pop();
                        int b = stack.pop();
                        stack.push(b - a);
                    }
                    else {
                        stack.push(Integer.parseInt(tokens[i]));
                    }
                else if (ch == '*') {
                    int a = stack.pop();
                    int b = stack.pop();
                    stack.push(b * a);
                }
                else if (ch == '/') {
                    int a = stack.pop();
                    int b = stack.pop();
                    stack.push(b / a);
                }
            }

            System.out.println("Answer = " + stack.pop());
        }
        input.close();
    }
}