2020.4.28

public static void main(String[] args) {
        mainMenu();
    }

    public static void mainMenu() {
        Scanner input = new Scanner(System.in);
        System.out.println("1.登录");
        System.out.println("2.注册");
        System.out.println("3.幸运抽奖,输入四位会员卡号,如果百位等于系统随机数,就是星运会员.否则不是.");
        System.out.println("4.看小故事,");
        System.out.println("5.退出系统");
        System.out.println("请选择");
        int i = input.nextInt();
        switch (i) {
            case 1:
                login();
                break;
            case 2:
                zhuce();
                break;
            case 3:
                choujiang();
                break;
            case 4:
                sgs();
                break;
            case 5:
                break;

        }
    }



    private static void sgs() {
        System.out.println("一个小故事");
        returnMain();
    }

    private static void choujiang() {
        Random r=new Random();
        int i1 = r.nextInt(10);
        System.out.println("请输入四位会员卡号");
        Scanner input = new Scanner(System.in);
        int i = input.nextInt();
        if (i1==i%1000/100){
            System.out.println("恭喜你中奖了");
        }else {
            System.out.println("很遗憾你没有中奖");
        }
        returnMain();

    }

    private static void login() {
        // TODO Auto-generated method stub
        Scanner input = new Scanner(System.in);
        System.out.println("输入用户名");
        String uname = input.next();
        System.out.println("输入密码");
        String upwd = input.next();
        if (uname.equals("zs") && upwd.equals("123")) {
            System.out.println("登录成功");
        } else {
            System.out.println("登录失败");
        }
        returnMain();

    }
    public static void returnMain(){
        System.out.println("是否返回主菜单?Y/N");
        Scanner input = new Scanner(System.in);
        if (input.next().equalsIgnoreCase("Y")) {
            mainMenu();
        }else{
            System.out.println("谢谢使用");
        }

    }
    public static void zhuce(){
        System.out.println("请输入用户名");
        Scanner input = new Scanner(System.in);
        String line = input.nextLine();
        System.out.println("请输入密码");
        int i = input.nextInt();
        login();

    }
}

　　

 public static void cj() {
        int sum=1;
        for(int i=1;i<=4;i++) {
            sum*=i;
        }
        System.out.println("4的阶乘="+sum);
    }
    public static void main(String[] args){
        // TODO 自动生成的方法存根
        cj();
    }
}

 public static void main(String[] args) {
        prn(2018);
    }
 
    public static void prn(int year) {
        if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
            System.out.println(year + "年是闰年");
        } else {
            System.out.println(year + "年不是闰年");
        }
 
    }