如果输入不正确，我需要重新输入，我该怎么做？

Question

如果输入不正确，我需要重新输入，我该怎么做？public static void main(String[] args) throws InterruptedException    {        String welcomeMessage = "Welcome to our system! Please enter your details to log in.\n";        System.out.println(welcomeMessage);        TimeUnit.SECONDS.sleep(3);        Scanner inputUserName = new Scanner(System.in);        String userName = "User Name: ";        System.out.println(userName);        String userNameInput = inputUserName.nextLine();        while (true)        {            if (userNameInput.contains("@"))            {                System.out.println("Shap");                break;            } else            {                System.out.println("\nPlease enter a valid user name!");                String enterAgain = userName;                System.out.println(enterAgain);            }        }    }

Answer 1

尝试在 while 条件中使用它

Scanner inputUserName = new Scanner(System.in); 

String userNameInput = inputUserName.nextLine();

while (!userNameInput.contains("@")) 

{

    System.out.println("\nPlease enter a valid user name!");

    userNameInput = inputUserName.nextLine(); 

}

System.out.println("Success");

Answer 2

您可以通过使用 while 循环来做到这一点 -

 Scanner inputUserName = new Scanner(System.in);

    String userName = "User Name: ";

        System.out.println(userName);

        String userNameInput = inputUserName.nextLine();

        while (!userNameInput.contains("@"))

        {

                System.out.println("\nPlease enter a valid user name!");

                System.out.println(userName);

                userNameInput = inputUserName.nextLine()

            }

        }

    System.out.println("Shap");