Reverse Polish Notation用堆栈实现逆波兰表达式

import java.io.IOException;
import java.util.*;
public class Class1
{
    public static void main(String[] args) throws IOException{
        String[] tokens = new String[]{"2","1","+","3","*"};
        System.out.println(evalRPN(tokens));
    }
    public static int evalRPN(String[] tokens){
        String operators="+-*/";
        Stack<String> stack=new Stack<String>();
        for(String t:tokens){
            if(!operators.contains(t)){
                stack.push(t);
            }else{
                int a=Integer.valueOf(stack.pop());
                int b=Integer.valueOf(stack.pop());
                switch(t){
                case "+":
                    stack.push(String.valueOf(a+b));
                    break;
                case "-":
                    stack.push(String.valueOf(b-a));
                    break;
                case "*":
                    stack.push(String.valueOf(a*b));
                    break;
                case "/":
                    stack.push(String.valueOf(b/a));
                    break;
                }
            }
        }
        return Integer.valueOf(stack.pop());
    }
}