带有Java堆栈的计算后修复符号

Question

我正在尝试建立一种将后缀符号评估为答案的方法。例如（6 8 +）将为14。从堆栈中弹出元素后，我是否必须构建一个单独的方法来添加元素？

private static double computePostfix(String postfix) {
        Scanner scan = new Scanner(postfix);
        StackInterface<Double> stack = new ArrayStack<>();
        // Read all tokens in the string expression
        while(scan.hasNext()) {
            String token = scan.next();
            switch(token) { // Consider different values for token
            case "+":

                // Loops only through numbers for this addition operation
                while(!Double.isNaN(stack.peek())) {
                    // TODO: pop and add up 
                  Double sum =+ stack.pop();
                }
                stack.pop(); // Remove the NaN
                // TODO: Push the sum back on the stack
                stack.push(newEntry);
                break;
            case "*":
                // TODO: Similar to +
                break;
            case "-":
                // TODO: Hard, and has special cases
                break;
            case "/":
                // TODO: Hard, and has special cases
                break;
            case "(":
                // Indicates start of a new operation
                stack.push(Double.NaN);
                break;
            case ")":
                break;
            default: // Should be a number
                stack.push(Double.parseDouble(token));
            }
        }
        scan.close();
        double answer = stack.pop(); // Should only be one item: the answer
        if(!stack.isEmpty()) {
            // Crash program: this expression was invalid
            throw new IllegalArgumentException();
        }
        return answer;
    }

Answer 1

您的错误是Double sum =+ stack.pop();变量sum必须在while循环之前。并将拼写错误=+更改为+=