java - 第二次运行方法时出现"No such element"错误

Question

这个问题已经有答案了:

Close a Scanner linked to System.in (5 个回答)

How to use java.util.Scanner to correctly read user input from System.in and act on it? (1 个回答)

已关闭 5 年前。

抱歉，如果这是一个愚蠢的问题，我是一个编程菜鸟，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 方法在运行一次时有效，但在第二次运行时出现以下错误。

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一个未在某处消耗的换行符，但我似乎无法弄清楚。为什么我会收到此错误？我该如何修复它？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用相同的 Scanner。

通过关闭Scanner，您还将关闭其输入源，在本例中为System.in。因此，用户不能再输入任何内容。

下面是更正后的代码片段:

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.");
}