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public static void main(String[] args) {

//键盘录入

    Scanner sc =new Scanner(System.in);

    double number1;

    double number2;

    //选项

    int choose =0;

    System.out.println("欢迎使用计算器 1:加法 2减法");

    choose = sc.nextInt();

    System.out.println("请输入Number1:");

    number1 = sc.nextDouble();

    System.out.println("请输入Number2:");

    number2 = sc.nextDouble();

  double result=Sum(number1, number2, choose);

    System.out.println("结果为:"+result);

}

//方法

private static double Sum(double n1,double n2,int choose){

if (choose==2){

return n1-n2;

    }

return n1+n2;

}