算法第四版 用java实现由中序表达式转换为后续表达式

遇到数字时压入datastack栈，遇到操作符压入optrstack栈，遇到右括号时取出datastack的两个数，与操作符组成一个字符串继续压入datastack

import java.util.Stack;public class InfixToPostfix {    private String infixToPostfix(String str)    {        Stack<String> dataStack = new Stack<>();        Stack<String> optrStack = new Stack<>();        for (int i = 0; i < str.length(); i++)        {            if(isDigital(str.charAt(i)))//处理数字                dataStack.push(String.valueOf(str.charAt(i)));            else if(isOperator(str.charAt(i)))//处理操作符                optrStack.push(String.valueOf(str.charAt(i)));            else if(str.charAt(i) == ')')//处理右括号的情况            {                String d1 = dataStack.pop();                String d2 = dataStack.pop();                String opt = optrStack.pop();                String ext = d2 + d1 + opt;                dataStack.push(ext);            }            else if(str.charAt(i) == '(')                continue;        }        while(optrStack.size() > 0)        {            String d1 = dataStack.pop();            String d2 = dataStack.pop();            String opt = optrStack.pop();            String ext = d2 + d1 + opt;            dataStack.push(ext);        }        return dataStack.pop();    }    private boolean isOperator(char ch)    {        return ch == '+' || ch == '-' || ch == '*' || ch == '/';    }    private boolean isDigital(char ch)    {        return ch <= '9' && ch >= '0';    }    public static void main(String[] args)    {        String str = "(1+2)*(3*(4+5))";        InfixToPostfix ip = new InfixToPostfix();        String res = ip.infixToPostfix(str);        System.out.println(res);    }}