NoSuchElement Exception

Question

Can someone please help explain why this is throwing a NoSuchElement exception? It seems to happen at the last line scan.nextInt();

I am trying to read in names from a file and sort them into an array and then read in an option from the user after printing.

import java.util.ArrayList;
import java.util.Collections;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.NoSuchElementException;
import java.util.Scanner;

public class DeletingNames {

    public static void main(String[] args)throws Exception {
        int addDelete = 0;
        int index = 0;
        String addName;
        String deleteName;

        File namesFile = new File("names.txt");

        ArrayList<String> names = new ArrayList<String>();

        try {
            Scanner scan = new Scanner(namesFile);

            while(scan.hasNext()){
                names.add(scan.next());
                index++;
            }

            Collections.sort(names);

            System.out.println(names);
            System.out.println();

            System.out.print("Add/delete data?\n1. Add\n2. Delete");

            addDelete = scan.nextInt();

            scan.close();
        }

        catch (FileNotFoundException e){
            System.err.println("File not found");
        }
    }
}

Answer 1

Your Scanner is still referencing the file not System.in:

scan.close();
scan = new Scanner(System.in);
addDelete = scan.nextInt();

You already went through the whole file so there are no more elements. That is why you are getting NoSuchElement exception...

Answer 2

From the Javadoc:

A NoSuchElementException is Thrown by the nextElement method of an Enumeration to indicate that there are no more elements in the enumeration.

The execution flow won't leave this loop

while(scan.hasNext()){
    names.add(scan.next());
    index++;
}

....
// 'scan' here is invalid, create a new System.in scanner
System.out.print("Add/delete data?\n1. Add\n2. Delete");
addDelete = scan.nextInt(); // Invalid call

code block until there are no more elements to read from the text file. So calling scan.nextInt() would throw a NoSuchElementException. You need a new Scanner to read the user's input.

Answer 3

Your while loop goes through everything in the scanner (scan.hasNext();), so there's nothing left when you come to "addDelete = scan.nextInt();"

If you want to take input from the user, you need to create a new scanner.