1  import java.util.Scanner;

  2  import java.util.Stack;

  3  

  4  /**

  5     This calculator uses the reverse polish notation.

  6  */

  7  public class Calculator

  8  {

  9     public static void main(String[] args)

 10     {

 11        Scanner in = new Scanner(System.in);

 12        Stack<Integer> results = new Stack<Integer>();

 13        System.out.println("Enter one number or operator per line, Q to quit. ");

 14        boolean done = false;

 15        while (!done)

 16        {         

 17           String input = in.nextLine();

 18  

 19           // If the command is an operator, pop the arguments and push the result

 20  

 21           if (input.equals("+"))

 22           {

 23              results.push(results.pop() + results.pop());

 24           }

 25           else if (input.equals("-"))

 26           {

 27              Integer arg2 = results.pop();

 28              results.push(results.pop() - arg2);

 29           }

 30           else if (input.equals("*") || input.equals("x"))

 31           {

 32              results.push(results.pop() * results.pop());

 33           }

 34           else if (input.equals("/"))

 35           {

 36              Integer arg2 = results.pop();

 37              results.push(results.pop() / arg2);

 38           }

 39           else if (input.equals("Q") || input.equals("q"))

 40           {

 41              done = true;

 42           }

 43           else 

 44           {

 45              // Not an operator--push the input value

 46              

 47              results.push(Integer.parseInt(input));

 48           }

 49           System.out.println(results);

 50        }

 51     }

 52  }