创建一个计算器，使用scanner从单独的类调用方法

import java.util.Scanner;

public class Calculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        
        System.out.print("请输入第一个数字: ");
        double num1 = scanner.nextDouble();
        
        System.out.print("请输入操作符 (+, -, *, /): ");
        String operator = scanner.next();
        
        System.out.print("请输入第二个数字: ");
        double num2 = scanner.nextDouble();
        
        double result = 0;
        
        switch (operator) {
            case "+":
                result = add(num1, num2);
                break;
            case "-":
                result = subtract(num1, num2);
                break;
            case "*":
                result = multiply(num1, num2);
                break;
            case "/":
                result = divide(num1, num2);
                break;
            default:
                System.out.println("无效的操作符");
                return;
        }
        
        System.out.println("计算结果: " + result);
    }
    
    public static double add(double num1, double num2) {
        return num1 + num2;
    }
    
    public static double subtract(double num1, double num2) {
        return num1 - num2;
    }
    
    public static double multiply(double num1, double num2) {
        return num1 * num2;
    }
    
    public static double divide(double num1, double num2) {
        return num1 / num2;
    }
}