为什么会收到NoSuchElementException？

Question

I recently started learning about FileIO and created a simple program that has the user input their name and age. The program compiles fine, but when I run the program, I get the following message:

Exception in thread "main" java.util.NoSuchElementException
        at java.util.Scanner.throwFor(Scanner.java:862)
        at java.util.Scanner.next(Scanner.java:1371)
        at FileIO.main(FileIO.java:18)

I am unsure what this compiler error means and I would appreciate if someone could explain it to me. Thanks!

import java.util.*;
import java.io.*;

public class FileIO
{
        public static void main( String args[] )
        {
                String sourceFile = "inputfile.txt";
                String destinationFile = "outputfile.txt";
                try{

                        File sfile = new File(sourceFile);
                        Scanner input = new Scanner(sfile);

                        while(input.hasNext())
                        {
                                String fname = input.next();
                                String lname = input.next();
                                int age = input.nextInt();
                                System.out.println(fname + ' ' + lname + ", your age is: " + age);

                        }
                        input.close();

                }catch(IOException ex){
                        System.err.println(ex);
                }

        }
}

Answer 1

I will assume one line of your input is something like this:

Joe C

In this case, your first call to next() will return Joe , and the second one will return C . When you now call nextInt() , there is nothing left here to read. Hence the NoSuchElementException .

Answer 2

You could change it like this:

import java.util.*;
import java.io.*;

public class FileIO
{
    public static void main( String args[] )
    {
            String sourceFile = "inputfile.txt";
            String destinationFile = "outputfile.txt";
            try{

                    File sfile = new File(sourceFile);
                    Scanner input = new Scanner(sfile);

                    while(input.hasNext())
                    {
                            String fname = input.next();
                            String lname = "";
                            if (input.hasNext())
                                lname = input.next();
                            int age = -1;
                            if (input.hasNext())
                                age = input.nextInt();
                            System.out.println(fname + ' ' + lname + ", your age is: " + age);

                    }
                    input.close();

            }catch(IOException ex){
                    System.err.println(ex);
            }

    }
}

Answer 3

Your program works fine !

Make sure the inputfile.txt is like:

String
String
int

and exists in the working directory. to find the working directory you can add this to your code:

System.out.println("Working Directory = " +  System.getProperty("user.dir"));