Java扫描器类没有这样的元素异常错误[重复]

Question

我有一个带有静态方法的类Test来获取输入。

 class Test {
        public static Student readStudent() throws IOException {
            Scanner s = new Scanner(System.in);
            System.out.println("Enter first name of student");
            String fname = s.nextLine();
            System.out.println("Enter middle name of student");
            String mname = s.nextLine();
            System.out.println("Enter last name of student");
            String lname = s.nextLine();
            System.out.println("Enter name format(1 for ',' and 2 for ';') ");
            int num = s.nextInt();
            System.out.println("Enter age of student");
            int age = s.nextInt();

            s.close();

            return new Student(new Name(String.join((num == 1) ? "," : ";", fname,
                    mname, lname)), age);

        }
    }

我可以接受一个学生的输入，但一旦我将其放入for循环，我就会得到一个java.util.NoSuchElementException:没有找到行错误。

这是我的循环

for (int i = 0; i < 10; i++) {
            Student s = Test.readStudent();
        }

为什么我会收到此错误？谢谢。

Answer 1

s.close（）;关闭当前 Scanner 对象，但也关闭所有基础流，在这种情况下 System.in。标准输入流关闭后，您将无法再打开它。

总而言之，最好在确定不再需要扫描程序后关闭它，并像这样重组代码：

Scanner sc = new Scanner(System.in);
for (int i = 0; i < 10; i++) {
    Student s = Test.readStudent(sc);
    // do something with your student object here
}
sc.close();

并将您的方法更改为

public static Student readStudent(Scanner s) throws IOException {
    Scanner s = new Scanner(System.in);
    System.out.println("Enter first name of student");
    String fname = s.nextLine();
    System.out.println("Enter middle name of student");
    String mname = s.nextLine();
    System.out.println("Enter last name of student");
    String lname = s.nextLine();
    System.out.println("Enter name format(1 for ',' and 2 for ';') ");
    int num = s.nextInt();
    s.nextLine(); // Need to consume new line
    System.out.println("Enter age of student");
    int age = s.nextInt();
    s.nextLine(); // Need to consume new line

    // no closing here

    return new Student(new Name(String.join((num == 1) ? "," : ";", fname,
                mname, lname)), age);
}