模拟简单的计算机程序

package base.method;

import java.util.Scanner;

public class Demo6 {
    public static String equal;
    public static double rest;
    public static double a;
    public static double c;
    public static String  b;
    public static void main(String[] args) {
        Demo6 calculator = new Demo6(); //创建对象调用函数
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入第一个数字");
         a = scanner.nextDouble();
        System.out.println("请输入运算符");
         b = scanner.next();
        System.out.println("请输入第二个数字");
         c = scanner.nextDouble();
        //double rest = 0;//存储最后的计算结果
        //if判断计算
        /*

        if (b.equals("-")){
            rest= calculator.sub(a,c);
        }else if (b.equals("+")){
            rest= calculator.add(a,c);
        }else if (b.equals("*")){
            rest= calculator.multiply(a,c);
        }else if (b.equals("/")){
            rest= calculator.div(a,c);
        }
        System.out.println("结果为："+rest);
         */
        //do while判断 switch循环
        do {
            switch (b) {
                case "+":
                    rest = add(a, c);
                    System.out.println("输入=获取结果：");
                    equal = scanner.next();
                    coninue();
                    break;
                case "-":
                    rest = sub(a, c);
                    System.out.println("输入=获取结果：");
                    equal = scanner.next();
                    coninue();
                    break;
                case "*":
                    rest =multiply(a, c);
                    System.out.println("输入=获取结果：");
                    equal = scanner.next();
                    coninue();
                    break;
                case "/":
                    rest = div(a, c);
                    System.out.println("输入=获取结果：");
                    equal = scanner.next();
                    coninue();
                    break;
                default:
                    System.out.println("请输入正确的运算符！");
            }
        }while (b.equals("+")||b.equals("-")||b.equals("*")||b.equals("/"));
        scanner.close();
    }

    //加法方法
    public static   double  add(double a,double b){
       return a+b;
    }
    //减法方法
    public static double sub(double a,double b){
        return a-b;
    }
    //乘法方法
    public static double multiply(double a,double b){
        return a*b;
    }
    //除法方法
    public static double div(double a,double b){
        return a/b;
    }
    //获得结果 或 再次输入 或重新计算
    public static void coninue(){
        Scanner scanner = new Scanner(System.in);
        if (equal.equals("=")){
            System.out.println(a+b+c+"="+rest);
            System.out.println("输入运算符+,-,*,/继续输入c 重新开始计算 或 输入其他字符结束");
            b=scanner.next();
            if (b.equals("+")||b.equals("-")||b.equals("*")||b.equals("/")){
                System.out.println("输入数字：");
                c = scanner.nextDouble();
                a=rest;
            } else if (b.equals("c")) {
                System.out.println("请输入第一个数字");
                a = scanner.nextDouble();
                System.out.println("请输入运算符");
                b = scanner.next();
                System.out.println("请输入第二个数字");
                c = scanner.nextDouble();

            } else {
                scanner.close();
                System.out.println("结束运算！");
            }
        }else {
            System.out.println("输入错误！");
        }
    }
}