四则运算Java实现

package cn.loosing.demo;
import java.util.*;
public class Test20210323_1 {
    // 运算符优先级map
    private static final Map OPT_PRIORITY_MAP = new HashMap() {
        private static final long serialVersionUID = 6968472606692771458L;

        {
            put('(', 0);
            put('+', 2);
            put('-', 2);
            put('*', 3);
            put('/', 3);
            put(')', 7);
        }
    };
    public static void main(String[] args) {
        String expr = "7*(2+3)*((((2+1))))";
        System.out.println(expr);
        Stack symbolStack = new Stack<>(); // 符号
        Stack optStack = new Stack<>(); // 运算
        List rpnList = new ArrayList<>(); //rpnList
        StringBuilder curNumBuilder = new StringBuilder(16); // 当前正在读取中的数值字符追加器
        
        expr.replaceAll(" ", "").chars().forEach(cht -> {
            char ch = (char) cht;
            if (!OPT_PRIORITY_MAP.containsKey(ch)) {
                curNumBuilder.append(ch);
                return;
            }
            if (curNumBuilder.length() != 0) {
                rpnList.add(curNumBuilder.toString());
                curNumBuilder.delete(0, curNumBuilder.length());
            }
            if (ch == '(')
                symbolStack.push(ch);
            else if (ch == ')')
                while ((ch = symbolStack.pop()) != '(') rpnList.add(String.valueOf(ch));
            else if (symbolStack.isEmpty() || OPT_PRIORITY_MAP.get(ch) > OPT_PRIORITY_MAP.get(symbolStack.lastElement()))
                symbolStack.push(ch);
            else {
                rpnList.add(String.valueOf(symbolStack.pop()));
                symbolStack.push(ch);
            }
        });
        if (curNumBuilder.length() != 0) rpnList.add(curNumBuilder.toString());
        while (!symbolStack.isEmpty()) rpnList.add(String.valueOf(symbolStack.pop()));

        System.out.println(rpnList);
        
        rpnList.forEach(str -> {
            if (!OPT_PRIORITY_MAP.containsKey(str.charAt(0))){
                optStack.push(str);
                return;
            }
            double d2 = Double.valueOf(optStack.pop());
            double d1 = Double.valueOf(optStack.pop());
            switch (str.charAt(0)) {
                case '+':
                    optStack.push(String.valueOf(d1 + d2));
                    break;
                case '-':
                    optStack.push(String.valueOf(d1 - d2));
                    break;
                case '*':
                    optStack.push(String.valueOf(d1 * d2));
                    break;
                case '/':
                    optStack.push(String.valueOf(d1 / d2));
            }
        });
        System.out.println(optStack);
    }
}