I'm trying to write a recursive function that evaluates a Queue as a mathematical expression. The queue can have any of the following characters: { '(', ')', ' ', '*'} or any single-digit number. I want to evaluate this expression and return the result. I can not use any loops or any data structures besides the q passed in as a parameter. This is what I have but I'm not quite sure why it's not working and I can't figure out how to add recursion.

public static int evaluate(Queue<Character> q) {
    if (q.peek().equals("(") || q.peek().equals(")")) {
        q.remove();
    }
    if (!(q.peek().equals(" ") || q.peek().equals("*"))) {
        int i = q.poll();
        if (q.poll().equals(" ")) {
            int x = q.poll();
            char d = (char)(i x);
            q.add(d);
        }
        int x;
    }
    return 1;
}

CodePudding user response：