中缀简单计算器

package 数据结构;

import java.util.Stack;

public class StackDemo {
    public static void main(String[] args) {
        Calculator calculator = new Calculator();
        System.out.println(calculator.calculate("700+2*6-4"));
    }
}

class Calculator{
    Stack numStack = new Stack<>();
    Stack operaStack = new Stack<>();

    int calculateByTwo(int num1, int num2, char opera){
        int res = 0;
        if (opera == '+') res =  num1 + num2;
        if (opera == '-') res = num2 - num1;
        if (opera == '*') res = num1 * num2;
        if (opera == '/') res = num2 / num1;
        return res;
    }
    int calculate(String str){
        int res = 0;
        int num1, num2;
        char opera;
        int index = 0;
        String keepNum = "";
        do {
            char ch = str.charAt(index);
            if (Character.isDigit(ch)) {
                keepNum = keepNum + ch;
                if (index+1 == str.length()){
                    numStack.push(Integer.parseInt(keepNum));
                }else if (isOpera(str.charAt(index+1))){
                    numStack.push(Integer.parseInt(keepNum));
                    keepNum = "";
                }

            }
            if (isOpera(ch)) {
                if (operaStack.isEmpty()) {
                    operaStack.push(ch);
                } else {
                    if (priority(ch) <= priority(operaStack.peek())) {
                        num1 = numStack.pop();
                        num2 = numStack.pop();
                        opera = operaStack.pop();
                        numStack.push(calculateByTwo(num1, num2, opera));
                        operaStack.push(ch);
                    } else {
                        operaStack.push(ch);
                    }
                }
            }
            index++;
        } while (index < str.length());
        while (!operaStack.isEmpty()) {
            //如果符号栈为空，代表数栈只剩一个数，即计算结果
            num1 = numStack.pop();
            num2 = numStack.pop();
            opera = operaStack.pop();
            numStack.push(calculateByTwo(num1, num2, opera));
        }
        res = numStack.pop();
        return res;
    }

    //判断是否操作符
    boolean isOpera(char c){
        return c == '+' || c == '-' || c == '*' || c == '/';
    }


    //判断优先级
    int priority(char c){
        return switch (c) {
            case '+', '-' -> 1;
            case '*', '/' -> 2;
            default -> -1;
        };
    }
}