为什么会收到NoSuchElementException？

Question

I'm getting this in my Eclipse console when I run my program:

Type a number then press enter.
1. Add a customer
2. Add an order
3. Remove an order
4. Ship an order
5. Print pending orders with customer information
6. Restock parts
7. Exit
1
Loading driver...
Driver loaded!
Connecting database...
Database connected!
Enter 5 letters or less to identify the customer as.
Exception in thread "main" java.util.NoSuchElementException: No line found
    at java.util.Scanner.nextLine(Scanner.java:1540)

I've tried using just one Scanner and not closing it, but that didn't work. Can someone please help me figure out why I'm getting this message on the line that reads, tempCustID = keyboard1.nextLine(); ? What's weird is that no error occurs during the previous line that reads, int seed = keyboard.nextInt(); .

Here's the code for my Menu.java class:

import java.sql.Connection;
import java.sql.SQLException;

public class Menu {

    public static void main(String[] args) throws SQLException {
        // TODO Auto-generated method stub

        DatabaseModifier session = new DatabaseModifier();
        int seed = session.options();
        Connection mycon = session.connectDB();

        while(seed != 7) {
            if(seed == 1) {
                session.addCust(mycon);
            }else if(seed == 2) {
                //session.addOrder(mycon);
            }else if(seed == 3) {

            }else if(seed == 4) {

            }else if(seed == 5) {

            }else if(seed == 6) {

            }else {
                System.out.println("Invalid option.");
            }
            seed = session.options();
        }
        System.out.println("Good-bye.");
    }
}

And here's the code for my DatabaseModifier.java class:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Scanner;

public class DatabaseModifier {

    public int options() {      
        System.out.println("Type a number then press enter.");
        System.out.println("1. Add a customer");
        System.out.println("2. Add an order");
        System.out.println("3. Remove an order");
        System.out.println("4. Ship an order");
        System.out.println("5. Print pending orders with customer information");
        System.out.println("6. Restock parts");
        System.out.println("7. Exit");

        Scanner keyboard = new Scanner(System.in);
        int seed = keyboard.nextInt();
        keyboard.close();

        return seed;
    }

    public Connection connectDB() {
        String url = "jdbc:mysql://localhost:3306/northwind?useSSL=false&serverTimezone=EST";
        String username = "root";
        String password = "password";

        System.out.println("Loading driver...");

        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            System.out.println("Driver loaded!");
        }catch (ClassNotFoundException e) {
            throw new IllegalStateException("Cannot find the driver in the classpath!", e);
        }

        System.out.println("Connecting database...");

        try {
            Connection mycon = DriverManager.getConnection(url, username, password);
            System.out.println("Database connected!");
            return mycon;
        } catch (SQLException e) {
            throw new IllegalStateException("Cannot connect the database!", e);
        }
    }

    public void addCust(Connection mycon) throws SQLException {
        String tempCustID, custID, comp, contName, contTitle, addr, city, reg, postCode, country, phone, fax;

        Scanner keyboard1 = new Scanner(System.in);

        int correctInput = 0;
        do {
            PreparedStatement stat = mycon.prepareStatement("SELECT CustomerID FROM customers");
            ResultSet cust = stat.executeQuery();
            System.out.println("Enter 5 letters or less to identify the customer as.");
            tempCustID = keyboard1.nextLine();
            custID = tempCustID.toUpperCase();
            while (cust.next()) {
                String customerID = cust.getString("CustomerID");
                if (custID.equals(customerID) || "".equals(custID) || "NULL".equals(custID) || "null".equals(custID) || custID.length() > 5) {
                    System.out.println(
                            "Customer ID already exists or you entered incorrect input. Please enter a different sequence of 5 letters or less to identify the customer as.");
                }else
                    correctInput = 1;
            }
        }while(correctInput == 0);

        correctInput = 0;
        do {
            PreparedStatement stat1 = mycon.prepareStatement("SELECT CompanyName FROM customers");
            ResultSet comp1 = stat1.executeQuery();
            System.out.println("Enter 40 letters or less to identify the company name.");
            comp = keyboard1.nextLine();
            while (comp1.next()) {
                String compName = comp1.getString("CompanyName");
                if (compName.equals(comp) || "".equals(comp) || "NULL".equals(comp) || "null".equals(comp) || comp.length() > 40) {
                    System.out.println(
                            "Company name already exists or you entered incorrect input. Please enter a different sequence of 40 letters or less to identify the company as.");
                }else
                    correctInput = 1;
            }
        }while(correctInput == 0);

        correctInput = 0;
        do {
            System.out.println("Enter 30 letters or less to identify the contact's first and last name.");
            contName = keyboard1.nextLine();
            if ("".equals(contName) || "NULL".equals(contName) || "null".equals(contName) || contName.length() > 30) {
                System.out.println("Incorrect input.");
            }else
                correctInput = 1;
        }while(correctInput == 0);


        correctInput = 0;
        do {
            System.out.println("Enter 30 letters or less to identify the contact's job title.");
            contTitle = keyboard1.nextLine();
            if ("".equals(contTitle) || "NULL".equals(contTitle) || "null".equals(contTitle) || contTitle.length() > 30) {
                System.out.println("Incorrect input.");
            }else
                correctInput = 1;
        }while(correctInput == 0);


        correctInput = 0;
        do {
            System.out.println("Enter 60 letters or less to identify the company's address.");
            addr = keyboard1.nextLine();
            if ("".equals(addr) || "NULL".equals(addr) || "null".equals(addr) || addr.length() > 60) {
                System.out.println("Incorrect input.");
            }else
                correctInput = 1;
        }while(correctInput == 0);

        correctInput = 0;
        do {
            System.out.println("Enter 15 letters or less to identify the company's city.");
            city = keyboard1.nextLine();
            if ("".equals(city) || "NULL".equals(city) || "null".equals(city) || city.length() > 15) {
                System.out.println("Incorrect input.");
            }else
                correctInput = 1;
        }while(correctInput == 0);

        correctInput = 0;
        do {
            System.out.println("Enter 15 letters or less to identify the company's region.");
            reg = keyboard1.nextLine();
            if ("".equals(reg) || "NULL".equals(reg) || "null".equals(reg) || reg.length() > 15) {
                System.out.println("Incorrect input.");
            }else
                correctInput = 1;
        }while(correctInput == 0);

        correctInput = 0;
        do {
            System.out.println("Enter 10 letters or less to identify the company's postal code.");
            postCode = keyboard1.nextLine();
            if ("".equals(postCode) || "NULL".equals(postCode) || "null".equals(postCode) || postCode.length() > 10) {
                System.out.println("Incorrect input.");
            }else
                correctInput = 1;
        }while(correctInput == 0);

        correctInput = 0;
        do {
            System.out.println("Enter 15 letters or less to identify the company's country.");
            country = keyboard1.nextLine();
            if ("".equals(country) || "NULL".equals(country) || "null".equals(country) || country.length() > 15) {
                System.out.println("Incorrect input.");
            }else
                correctInput = 1;
        }while(correctInput == 0);

        correctInput = 0;
        do {
            System.out.println("Enter 24 letters or less to identify the company's phone number.");
            phone = keyboard1.nextLine();
            if ("".equals(phone) || "NULL".equals(phone) || "null".equals(phone) || phone.length() > 24) {
                System.out.println("Incorrect input.");
            }else
                correctInput = 1;
        }while(correctInput == 0);

        correctInput = 0;
        do {
            System.out.println("Enter 24 letters or less to identify the company's fax.");
            fax = keyboard1.nextLine();
            if ("".equals(fax) || "NULL".equals(fax) || "null".equals(fax) || fax.length() > 24) {
                System.out.println("Incorrect input.");
            }else
                correctInput = 1;
        }while(correctInput == 0);

        keyboard1.close();

        PreparedStatement newCust = mycon.prepareStatement(
                "INSERT INTO customers" + "(CustomerID, CompanyName, ContactName, ContactTitle, Address, "
                        + "City, Region, PostalCode, Country, Phone, Fax)" + "VALUES(?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)");
        newCust.setString(1, custID);
        newCust.setString(2, comp);
        newCust.setString(3, contName);
        newCust.setString(4, contTitle);
        newCust.setString(5, addr);
        newCust.setString(6, city);
        newCust.setString(7, reg);
        newCust.setString(8, postCode);
        newCust.setString(9, country);
        newCust.setString(10, phone);
        newCust.setString(11, fax);
        newCust.executeUpdate();
    }

Answer 1

Expanding upon and clarifying user3170251's comment, closing a Scanner also closes the underlying data source if that source is in fact Closeable :

If this scanner has not yet been closed then if its underlying readable also implements the Closeable interface then the readable's close method will be invoked. If this scanner is already closed then invoking this method will have no effect.

( Scanner.close() javadocs )

As an InputStream , your input source, System.in , is indeed Closeable . And once it is closed, it is closed -- nothing further can be read from it, even if you wrap it in a new Scanner . This is why your second and subsequent invocations of DataBaseModifier.options() throw.

The solution is to avoid closing System.in . Moreover, it would be safest to reuse a single Scanner instead of creating a new one, as it is possible for data to be buffered inside the Scanner and lost when you close it. There are several ways to approach that problem, but a pretty simple one would be to make your Scanner an instance variable instead of a local variable. Initialize it when you instantiate the class, and leave it open forever.