关于java中通过逆波兰式实现不带括号的四则运算，求教解决方法

import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.util.Stack;import java.util.regex.Matcher;import java.util.regex.Pattern;public class Expression{    public static void main(String args[]){                 //得到输入的算数表达式        String s=new String();        System.out.println("输入算数表达式：");        BufferedReader bf=new BufferedReader(new InputStreamReader(System.in));        try {            s=bf.readLine();        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }                //通过正则表达式判断输入的是否正确        Pattern p=Pattern.compile("([1-9][0-9]*[+\\-\\*/])+[1-9][0-9]*");        Matcher m=p.matcher(s);        if((m.matches()==true)){            Expression ex=new Expression();            ex.getExpression(s);                    }else{            System.out.println("表达式输入有误！");                    }    }        //把算数表达式转化为后缀式（逆波兰式）    private String getExpression(String expression){        //存放操作符的栈        Stack<Character> s1=new Stack<Character>();        Stack<Object> s2=new Stack<Object>();                int len=expression.length();        //System.out.println(len);        char c1;                for(int i=0;i<len;i++){            c1=expression.charAt(i);            //s1.push('#');            System.out.println(c1);                        if(isOperator(c1)==true){                //System.out.println(c1);                //操作数为操作符且优先级比s1栈顶操作符优先级高时，直接把操作符压入s1                if(s1.empty()){                    s1.push(c1);                    //System.out.println(c1);                }                else {                    if(priorityCompare(c1,s1.peek())==1){                        s1.push(c1);                        //System.out.println(s1.peek());                    }                                                        else{                        //弹出s1栈顶的操作符并压入s2，直到c1优先级小于s1栈顶的操作符优先级                        while(priorityCompare(c1,s1.peek())!=1){                             s2.push(s1.pop());                            System.out.println(s2.peek());                        }                        s1.push(c1);                        //System.out.println(s1.peek());                    }                }            }else{                //若操作数为数字，直接压入s2中                s2.push(c1);                //System.out.println(c1);            }        }        //把s1中剩余的元素压入s2中        while(!s1.isEmpty()){            s2.push(s1.pop());            //System.out.println(s1.peek());        }        return count_result(s2);     }    //根据后序的计算出结果    private String count_result(Stack<Object> ob) {        //存放后序的栈        Stack<Object> s3=new Stack<Object>();        //计算结果的栈        Stack<Double> s4=new Stack<Double>();                while(!ob.isEmpty()){            s3.push(ob.pop());        }                while(!s3.isEmpty()){            if(!isOperator(s3.peek())){                    s4.push((Double)(s3.pop()));                                }            else{                    s4.push(cout(s4.pop(),s4.pop(),(char)s3.pop()));                            }        }                return Double.toString(s4.peek());    }    private Double cout(double x, double y, char z) {        double result=0;        switch(z){        case '+':            result=x+y;            break;        case '-':            result=x-y;            break;        case '*':            result=x*y;            break;        case '/':            result=x/y;            break;                    }        //System.out.println(result);        return result;    }        //比较两个操作符的优先级    private int priorityCompare(char c1, char c2) {        switch(c1){        case '+':        case '-':            return(c2=='*'||c2=='/'?-1:0);        case '*':        case '/':            return(c2=='+'||c2=='-'?1:0);        }        return 1;        //return getPriority(c1) - getPriority(c2);            }    /*int getPriority(char c) {        if(c == '+' || c == '-')            return 1;        else             return 2;    }*/        //检测是否是操作符    private boolean isOperator(Object o){        //System.out.println("isO:"+o);        char c1=(char)o;        //System.out.println("isO:"+c1);            if(c1=='+'||c1=='-'||c1=='*'||c1=='/'){                //System.out.println("yes");                return true;            }            else{                //System.out.println("no");                return false;            }                    }}