Write a function that parses a string containing sum and multiplication operations and returns the result

Question

tersduz · Accepted Answer

public static void main(String[] args)
    {
        String exp = "2 + 4 + 1 + 6 + 7";
        Stack numbers = new Stack();
        Stack ops = new Stack();

        StringTokenizer t = new StringTokenizer(exp, " ");
        while (t.hasMoreTokens()) {
            String token = t.nextToken();
            boolean isNumber = false;
            int n = 0;
            try {
                n = Integer.parseInt(token);
                isNumber = true;
            } catch(NumberFormatException e) {
            }

            if (isNumber) {
                numbers.push(n);
                continue;
            }
            //it's an operator
            if (ops.isEmpty()) {
                ops.push(token);
                continue;
            }

            while (!ops.isEmpty() && token.equals("+")) {
                String op = ops.pop();
                numbers.push(apply(op, numbers.pop(), numbers.pop()));
            }

            ops.push(token);
        }

        while (!ops.isEmpty()) {
            String op = ops.pop();
            numbers.push(apply(op, numbers.pop(), numbers.pop()));
        }

        System.out.println(numbers.pop());
    }

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