java 实现一个简易计算器

import java.util.Scanner;
public class Test {    public static void main(String[] args) {

        count();
    }

public static void count() {
        Scanner input1 = new Scanner(System.in);
        System.out.println("输入一个数");
double a = input1.nextDouble();
while (true) {
            Scanner input3 = new Scanner(System.in);
            System.out.println("提示：请输入您的操作");
            System.out.println("+");
            System.out.println("-");
            System.out.println("*");
            System.out.println("/");
            System.out.println("F:退出");
            String str = input3.nextLine();
char chr = str.toCharArray()[0];
switch (chr) {
case '+':
                a = add(a);
            System.out.println("当前结果为："+a);
break;
case '-':
                a = subtrace(a);
                System.out.println("当前结果为："+a);
break;
case '*':
                a = ride(a);
                System.out.println("当前结果为："+a);
break;
case '/':
                a = except(a);
                System.out.println("当前结果为："+a);
break;
case 'F':
                System.out.println("结果:" + a);
                System.exit(-1);

default:
                System.out.println("操作错误！");
break;
            }
        }
    }

public static double add(double a) {
        Scanner input2 = new Scanner(System.in);
        System.out.println("输入一个数");
double b = input2.nextDouble();
return (a + b);
    }

public static double subtrace(double a) {
        Scanner input2 = new Scanner(System.in);
        System.out.println("输入一个数");
double b = input2.nextDouble();
return (a - b);

    }

public static double ride(double a) {
        Scanner input2 = new Scanner(System.in);
        System.out.println("输入一个数");
double b = input2.nextDouble();
return a * b;

    }

public static double except(double a) {
        Scanner input2 = new Scanner(System.in);
        System.out.println("输入一个数");
double b = input2.nextDouble();
return a / b;

    }
}