仅适用于习题类型的表达式，对于 x*y*z+m、x+(y-z)*m + n这类型的表达式题并不适合

package StackTest;

import java.util.ArrayList;

import java.util.Deque;

import java.util.LinkedList;

import java.util.List;

import java.util.Queue;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

import static tools.LogUtils.log;

public class rulesCalcInStack {

public static void main(String[] args) {

String exp = "1 + 2 * (9 - 5)";

        SuffixExpression se = compile(exp);

        int result = se.execute();

        log.info(exp + " = " + result + " " + (result == 1 + 2 * (9 - 5) ? "✓" : "✗"));

    }

static SuffixExpression compile(String exp) {

        Deque<String> num=new LinkedList<>();

        Deque<String> opr=new LinkedList<>();

        String[] list =null;

        String regEx="[^0-9]";  

        String regExOpr="[^+-/%/*]";

        //从exp提取数字并入栈

        Pattern p = Pattern.compile(regEx);  

        Matcher m = p.matcher(exp);  

        if (m.find()) {

           list=m.replaceAll(",").trim().toString().replaceAll(",+", ",").split(",");

           //log.info(list[1]);

        }

        for(String str:list) {

        num.push(str);

        }

        //从exp提取运算符号并入栈

        p= Pattern.compile(regExOpr);

        m = p.matcher(exp);

        list =null;

        if (m.find()) {

            String str=trimChar(m.replaceAll(",").trim().toString().replaceAll(",+", ","),',');

            log.info(str);

            list=str.split(",");

         }

        for(String operator:list) {

        opr.push(operator);

        }

        return new SuffixExpression(num,opr);  

}

//去除字符串首尾指定的字符

public static String trimChar(String str,char ch) {

if(str.charAt(0)==ch) {

str=str.substring(1);

};

if(str.charAt(str.length()-1)==ch) {

str=str.substring(0, str.length()-1);

}

//log.info(str);

return str;

}

}

class SuffixExpression {

private Deque<String> num=new LinkedList<>();

    private Deque<String> opr=new LinkedList<>();

    public SuffixExpression(Deque<String> num,Deque<String> opr) {

    this.num=num;

    this.opr=opr;

    }

    //计算

    int execute() {

        int result=0;

        do {

String operator=this.opr.pop();

String num1=this.num.pop();

String num2=this.num.pop();

switch (operator) {

case "-":

result=Integer.parseInt(num2)-Integer.parseInt(num1);

break;

case "+":

result=Integer.parseInt(num2)+Integer.parseInt(num1);

break;

case "/":

result=Integer.parseInt(num2)/Integer.parseInt(num1);

break;

case "*":

result=Integer.parseInt(num2)*Integer.parseInt(num1);

break;

case "%":

result=Integer.parseInt(num2)*Integer.parseInt(num1);

break;

default:

throw new IllegalArgumentException("Unexpected operator: " + operator);

}

this.num.push(String.valueOf(result));

      } while (this.num.size()>1);

      log.info(this.num.peek());

        return Integer.valueOf(this.num.peek());

    }

}