逆波兰式求解多项式

import java.util.Stack;
public class Solution {
    //逆波兰式求解多项式计算
    public int evalRPN(String[] tokens) {
        if(tokens==null)
            return 0;
        if(tokens.length==1&&tokens[0]!="+"
          &&tokens[0]!="-"&&tokens[0]!="*"&&tokens[0]!="/")
         return Integer.parseInt(tokens[0]);
        Stack<Integer>stack=new Stack<Integer>();
        stack.push(Integer.parseInt(tokens[0]));
        stack.push(Integer.parseInt(tokens[1]));
        int temp1=0;
        int temp2=0;
        for(int i=2;i!=tokens.length;i++)
        {
            if(tokens[i].equals("+"))
            {
               temp1=stack.pop();
               temp2=stack.pop();
               stack.push(temp1+temp2);
            }else if(tokens[i].equals("-"))
            {
               temp1=stack.pop();
               temp2=stack.pop();
               stack.push(temp2-temp1);

            }else if(tokens[i].equals("*"))
            {
               temp1=stack.pop();
               temp2=stack.pop();

               stack.push(temp1*temp2);
            }else if(tokens[i].equals("/"))
            {
               temp1=stack.pop();
               temp2=stack.pop();
               if(temp1==0||temp2==0)
               {
                   stack.push(0);
               }else{
                 stack.push(temp2/temp1);
               }

            }else{

               stack.push(Integer.parseInt(tokens[i]));
            }
        }
        return stack.pop();

    }

    //方法二:运用try-catch计算公式
    public int evalRPN2(String[] tokens) {
       if(tokens==null)
            return 0;
        if(tokens.length==1&&tokens[0]!="+"
          &&tokens[0]!="-"&&tokens[0]!="*"&&tokens[0]!="/")
         return Integer.parseInt(tokens[0]);

        Stack<Integer>stack=new Stack<Integer>();
        int a=0;
        int b=0;
        for(int i=0;i!=tokens.length;i++)
        {
          try{
            stack.add(Integer.parseInt(tokens[i]));

           }catch(Exception e){
            b=stack.pop();
            a=stack.pop();
            stack.push(compute(a,b,tokens[i]));
           }
        }
        return stack.pop();
    }

    public int compute(int a,int b,String operator)
    {
        switch (operator) 
        {
            case "+":
                return a+b;
            case "-":
                return a-b;
            case "*":
                return a*b;
            case "/":
                return a/b;
            default:
                return 0;

        }

    }

    public static void main(String[]args){
         //System.out.println("Hello");
        //String[]tokens={"2","1","+","3","*"};
        String[]tokens={"4","3","-"};
        Solution s=new Solution();
        System.out.println(s.evalRPN2(tokens));

    }
}