java模拟计算器代码

以下是Java模拟计算器的代码，实现了加减乘除和百分比的运算：

import java.util.Scanner;

public class Calculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要计算的表达式：");
        String expression = scanner.nextLine();
        double result = calculate(expression);
        System.out.println("计算结果为：" + result);
    }

    public static double calculate(String expression) {
        double result = 0;
        double num1 = 0;        double num2 = 0;
        char operator = ' ';
        int index = 0;
        int len = expression.length();

        while (index < len) {
            char ch = expression.charAt(index);
            if (ch == '+' || ch == '-' || ch == '*' || ch == '/') {
                operator = ch;
                index++;
            } else if (ch == '%') {
                if (operator == ' ') {
                    result = Double.parseDouble(expression.substring(0, index)) / 100;
                } else {
                    num2 = Double.parseDouble(expression.substring(index + 1)) / 100;
                    result = calculate(num1, num2, operator);
                }
                break;
            } else {
                int start = index;
                while (index < len && (Character.isDigit(expression.charAt(index)) || expression.charAt(index) == '.')) {
                    index++;
                }
                double num = Double.parseDouble(expression.substring(start, index));
                if (operator == ' ') {
                    num1 = num;
                } else {
                    num2 = num;
                    result = calculate(num1, num2, operator);
                    num1 = result;
                }
            }
        }
        return result;
    }

    public static double calculate(double num1, double num2, char operator) {
        double result = 0;
        switch (operator) {
            case '+':
                result = num1 + num2;
                break;
            case '-':
                result = num1 - num2;
                break;
            case '*':
                result = num1 * num2;
                break;
            case '/':
                result = num1 / num2;
                break;
        }
        return result;
    }
}