后缀表达式计算器

Question

我被指示有一个计算后缀表达式的方法。我得到一个输出，但我得到的输出是错误的数字。

static final char addition = '+', subtraction ='-', multiply = '*', divide = '/';
    @SuppressWarnings({ "rawtypes", "unchecked" })
    public static boolean evaluatePostfix(String lines, boolean check){
        if (check = false) {
            return false;
        }

        Stack expression = new Stack();

        String token;
        StringTokenizer tokenizer = new StringTokenizer(lines, " ");

        int operator1 = 0, operator2 = 0, result = 0;

        while (tokenizer.hasMoreTokens()) {
            token = tokenizer.nextToken(" ");

            if(token == " ") {
                System.out.print("");
            } else if (isOperator(token)) {
                operator2 = ((Integer) expression.pop()).intValue();
                operator1 = ((Integer) expression.pop()).intValue();
                result = evaluateOperator(token.charAt(0), operator1, operator2);
                expression.push(new Integer(result));
            } else {
                expression.push((Integer.parseInt(token)));
            }
        }

        System.out.println("The result of the expression is: " + result);
        return check = true;
    }

    //Checks expression from parameters passed through and evaluates
    private static int evaluateOperator(char charAt, int operator1, int operator2) {
        int result = 0;

        switch(charAt) {
        case addition:
            result = operator1 + operator2;
            System.out.println(result);
        case subtraction:
            result = operator1 - operator2;
            System.out.println(result);
        case multiply:
            result = operator1 * operator2;
            System.out.println(result);
        //case divide:
            //result = operator1 / operator2;           
        }
        return result;
    }

    //Checks whether operator is *,/,+,-. Returns true or false.
    public static boolean isOperator(char token) {
        switch(token) {
        case "-": case "/": case "+": case "*":
            return true;
        default:
            return false;
        }
    }

-

这是我得到的输出。正如您所看到的，计算开始正确，但随后进入纳尼亚。我无法弄清楚为什么。