第二次运行方法时出现“没有这样的元素”错误[重复]

Question

对不起，如果这是一个愚蠢的问题，我有点编程菜鸟，并且在使用以下代码时遇到了问题。

public static void main(String[] args) throws IOException {
    addName();
    addName();      //Line "10" in error
}

public static void addName() throws IOException {
    //Initializing Variables and Scanner
    Scanner keyboard = new Scanner(System.in);
    FileWriter fwriter = new FileWriter("Data.txt", true);
    PrintWriter outputFile = new PrintWriter(fwriter);
    int numFriends;
    String firstName;
    String lastName;
    String email;

    //Get number of entries to add
    System.out.print("How many people do you wish to add? ");
    numFriends = Integer.parseInt(keyboard.nextLine());        //Line "25" in error

    //Prompt for info and add it to the file
    for(int i = 1; i <= numFriends; i++){
        System.out.printf("Enter the first name of person %d: ",i);
        firstName = keyboard.nextLine();
        System.out.printf("Enter the last name of person %d: ",i);
        lastName = keyboard.nextLine();
        System.out.printf("Enter the email of person %d: ",i);
        email = keyboard.nextLine();

        outputFile.println(firstName + " " + lastName + " " + email);
    }

    //Wrap things up and give a confirmation
    outputFile.close();
    keyboard.close();
    System.out.println("Data written to the file.");;
}

addName 方法运行一次时有效，但第二次运行时出现跟随错误。

How many people do you wish to add? 1
Enter the first name of person 1: s
Enter the last name of person 1: d
Enter the email of person 1: g
Data written to the file.
How many people do you wish to add? Exception in thread "main" 
java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Unknown Source)
at Problem1.addName(Problem1.java:25)
at Problem1.main(Problem1.java:10)

我最初认为这是来自没有在某处使用的换行符，但我似乎无法弄清楚。为什么我会收到此错误？我该如何解决？谢谢！

Answer 1

您不应该在方法结束时关闭Scanner，理想情况下，您应该在整个执行过程中重复使用相同的Scanner。

通过关闭Scanner，您也关闭了它的输入源，在本例中为System.in。因此，用户无法再输入任何内容。

以下是修正后的 sn-p：

public static void main(String[] args) throws IOException {
    Scanner keyboard = new Scanner(System.in);
    addName(keyboard);
    addName(keyboard);
}

public static void addName(Scanner keyboard) throws IOException {
    FileWriter fwriter = new FileWriter("Data.txt", true);
    PrintWriter outputFile = new PrintWriter(fwriter);
    int numFriends;
    String firstName;
    String lastName;
    String email;

    //Get number of entries to add
    System.out.print("How many people do you wish to add? ");
    numFriends = Integer.parseInt(keyboard.nextLine());        //Line "25" in error

    //Prompt for info and add it to the file
    for(int i = 1; i <= numFriends; i++){
        System.out.printf("Enter the first name of person %d: ",i);
        firstName = keyboard.nextLine();
        System.out.printf("Enter the last name of person %d: ",i);
        lastName = keyboard.nextLine();
        System.out.printf("Enter the email of person %d: ",i);
        email = keyboard.nextLine();

        outputFile.println(firstName + " " + lastName + " " + email);
    }

    //Wrap things up and give a confirmation
    outputFile.close();
    System.out.println("Data written to the file.");
}