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");