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import java.util.Stack;import java.util.StringTokenizer;/** *  Programming Project 3-3 *   *  @author:(your name here) * *  Evaluates a postfix expression that operates on integer operands *  using the arithmetic operators +, -, *, /, and %.  Inputs is *  assumed to be in valid postfix form.*/public class PostfixEvaluator {    /**     * Helper method that parses the string and returns the int value.     * if the string is invalid, return -1.    */    private static int getIntValue(String s)    {        int result = -1;        try        {            result = Integer.parseInt(s);        }        catch (NumberFormatException e)        {            // does nothing        }        return result;    }// end getIntValue        /**    *  Evaluates the postfix expression and returns the result    */    public static double evaluate(String expression)    {        Stack stack = new Stack();        double first = 0.0;        double second = 0.0;                StringTokenizer tokenizer;        tokenizer = new StringTokenizer (expression);        while (tokenizer.hasMoreTokens()) {            char word = tokenizer.nextToken().charAt(0);            if(word == '+' || word == '-' || word == '*' || word == '/') {                    first = Double.parseDouble(stack.pop().toString());                    second = Double.parseDouble(stack.pop().toString());                }                switch (word) {                    case '+': stack.push(new Double(first + second)); break;                    case '-': stack.push(new Double(second - first)); break;                    case '*': stack.push(new Double(first * second)); break;                    case '/': stack.push(new Double(second / first)); break;                    default: stack.push(new Double(word - '0')); break;                }                          }                 // finish this method                return Double.parseDouble(stack.pop().toString());// change the 0.0 to the answer off of the stack    }// end evaluate        /**    *  main method, used for testing the static     *  method PostfixEvaluator.evaluate().  Can be    *  removed when testing complete.    */    public static void main (String args[])     {        System.out.println("Postfix Evaluator");        System.out.println("------- ---------");                String expression = "10 2 /";        System.out.println(expression);        System.out.println(PostfixEvaluator.evaluate(expression));                expression = "5 2 + 8 5 - *";        System.out.println("\n"+expression);        System.out.println("Result : " + PostfixEvaluator.evaluate(expression));                expression = "2 4 - 5 2 * +";        System.out.println("\n" + expression);        System.out.println("Result : " + PostfixEvaluator.evaluate(expression));            expression = "9 3 / 6 / 4 * 10 -";        System.out.println("\n" + expression);        System.out.println("Result : " + PostfixEvaluator.evaluate(expression));            expression = "9 3 / 6 / 4 * 10 - 4 /";        System.out.println("\n" + expression);        System.out.println("Result : " + PostfixEvaluator.evaluate(expression));    }//end main    }//end PostfixEvaluator