Java 如果输入不正确，我需要重新输入，我该怎么做？

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);
            }
        }
    }

---

尝试在while条件下使用此选项

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");

---

您可以使用while循环来实现这一点-

 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");

---

使用do while循环你可能有一个例子吗？是的。这个不错。但是，通过使用do while，您只能有一行input@HariPrasad你能举个例子吗？@BenCollins试试这个扫描仪inputUserName=new ScannerSystem.in；字符串userNameInput=；执行{System.out.println\n请输入有效的用户名！；userNameInput=inputUserName.nextLine；}while！userNameInput.contains@；