java - 如果用户输入不正确，如何让问题循环

Question

每当用户输入不正确的数据时，程序都会发出一条消息，告诉用户重试，但随后它会返回主菜单，而不是让用户尝试输入不同的值。我怎样才能做到这一点？

public void createStudentRecord(Scanner in)
{
    inputStudentID = null;
    inputMark = 0;

    System.out.println("Enter Student ID: ");
    in.nextLine();
    inputStudentID = in.nextLine();
    if (!(inputStudentID.length()==6))
    {
        System.out.println("Enter a student ID that is 6 characters");
    }
    else
    {
        System.out.println("Enter Module Mark: ");
        inputMark = in.nextInt();
        if (inputMark <0 || inputMark >100)
        {
            System.out.println("PLease enter a module mark between 0-100");
        }
        else
        {
            addStudent(inputStudentID, inputMark);
            System.out.println();
            System.out.println("New student record has been " + 
                        "successfully created");
            System.out.println();
            countRecords();
        }
    }
}

Answer 1

一种方法是循环，直到看到正确/所需的输入。这种方法的一个问题是，如果用户没有输入预期值(如果这是您正在寻找的值)，它永远不会终止，

代码片段:

public void createStudentRecord(Scanner in) {
    String inputStudentID = null;
    int inputMark = 0;

    while (true) {
        System.out.println("Enter Student ID: ");
        inputStudentID = in.nextLine();
        if (!(inputStudentID.length() == 6)) {
            System.out.println("Enter a student ID that is 6 characters");
        } else {
            break;
        }
    }

    while (true) {
        System.out.println("Enter Module Mark: ");
        inputMark = Integer.parseInt(in.nextLine());
        if (inputMark < 0 || inputMark > 100) {
            System.out.println("PLease enter a module mark between 0-100");
        } else {
            break;
        }
    }

    addStudent(inputStudentID, inputMark);
    System.out.println("\nNew student record has been successfully created.\n");
    countRecords();
}