逆波兰表达式

public static void main(String[] args) {
        //计算(3-1)*(2+5)的结果，结果为14，则我们是正确的
        String str= " 3 1 - 2 5 + *";
        String[] split = str.trim().split(" ");
        Stack<Integer> stack=new Stack<>();
        for(String s: split){
            if(s.trim().matches("^-?\d+$")){//判断是否是整数
                stack.push(Integer.valueOf(s));
            }else if(s.trim().equals("+")){
                Integer v1 = stack.pop();
                Integer v2 = stack.pop();
                stack.push(v2+v1);
            }else if(s.trim().equals("-")){
                Integer v1 = stack.pop();
                Integer v2 = stack.pop();
                stack.push(v2-v1);
            }else if(s.trim().equals("*")){
                Integer v1 = stack.pop();
                Integer v2 = stack.pop();
                stack.push(v2*v1);
            }else if(s.trim().equals("/")){
                Integer v1 = stack.pop();
                Integer v2 = stack.pop();
                stack.push(v2/v1);
            }else{
                System.out.println("非法字符");
            }
        }
        System.out.println("运算结果："+stack.pop());
    }