Why is the scanner not finding a line after the first iteration? - java.util.scanner

Question

I'm writing a program that basically acts as an email client as a part of a homework assignment for a class in java. I don't normally resort to the internet to answer my questions, but this is something that goes beyond what the professor is trying to get us to learn/practice, and I need to find a way to fix it.
The Problem: If I run the program, and input the second command (ri), it will prompt me for the number, and then finish by displaying the message, but immediately after, when it goes back into the second iteration of the .run() method the console returns:
Exception in thread "main" java.util.NoSuchElementException: No Line Found
at java.util.scanner.nextLine(Unknown Source)
Here's the code (I'm only including the important stuff...or at least what I think is important).
public class CmdLoop {
private MailClient _client;
Scanner kbd;
private Hashtable<String, ICommand> _commands = new Hashtable<String, ICommand>();
public CmdLoop(MailClient client) {
_client = client;
_commands.put("h", new client.cmd.Help());
_commands.put("ri", new client.cmd.ReadInbox());
kbd = new Scanner(System.in);
}
public void run2() {
System.out.print("\nMail: ");
String command = kbd.nextLine();
ICommand call = _commands.get(command);
if (command.equals("q"))
return;
else if (call == null)
System.out.println(command + " not understood, type h for help");
else if (call.equals(""))
System.out.println(command + " not understood, type h for help");
else call.run(_client);
this.run2();
}
and the ri class:
public class ReadInbox implements ICommand {
#Override
public void run(MailClient client) {
Scanner sc = new Scanner(System.in);
MailBox in = client.getInbox();
if(in.count() < 1)
System.out.println("Inbox empty");
else {
System.out.print("Enter the number of the message you would like to read: ");
int n = Integer.parseInt(sc.nextLine());
if(n > in.count())
System.out.println("Message number " + n + " can't be found");
else
in.getMessage(n - 1).show();
}
sc.close();
}
}
Basically it gets to the end of the ReadInbox.run() call, then it calls this.run2(), returns to the top, outputs "Mail: " and then returns the error. This is what the console looks like in my test:
Mail: ri
Enter the number of the message you would like to read: 1
Date: 2015/04/29 20:24:17
From: Charles Barkley (Charlie) <Charles#gmail.com>
Subj: testerino
this is another test
Mail: Exception in thread "main" java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Unknown Source)
at client.CmdLoop.run2(CmdLoop.java:28)
at client.CmdLoop.run2(CmdLoop.java:37)
at Main.main(Main.java:29)
If I'm correct, getting it so they both operate off the same scanner would solve my problem, and I feel like I should know how to do that, but I'm drawing a blank. Is there another way as well?

Answer 1

According to the documentation a Scanner will throw that exception "if no line was found". You can prevent that by first calling kbd.hasNextLine() which will tell you if there is something to get. That will wait for a line to be entered as long as the scanner is not closed.
Try this in your run2 method:
String command = null;
if (kbd.hasNextLine())
command = kbd.nextLine();
ICommand call = _commands.get(command);

Answer 2

I found the answer. I got rid of sc.close(); in the ReadInbox class. I have 0 clue why this works, but it does. If anyone has an explanation to offer, much appreciated, otherwise, whatever, at least it works.