Hashmap and array list problems

Question

This is an assignment I have to do and I do NOT expect anyone to do the coding for me. I am just looking for some direction as I have no clue where to go from here. Any guidance would be very welcomed.
We were given code that used just an Array lisThis is an assignment I have to do and I do NOT expect anyone to do the coding for me. I am just looking for some direction as I have no clue where to go next. Any guidance would be very welcomed.
We were given code and told to "Modify the MailServer so that it uses a HashMap to store MailItems. The keys to the HashMap should be the names of the recipients, and each value should be an ArrayList containing all the MailItems stored for that recipient. " Originally it was just an ArrayList named messages. There is also a MailClient and MailItem class.
I think I can post the messages using the HashMap now, but can't test it. I get a compiler error saying else without if even though I have an if statement. Even if I can compile, I need to make sure I am on the right track with the getNextMailItem method. It is the one I am stuck on and if I can get it to work, I can probably modify the other methods.
I would really appreciate feedback on that one method.
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
public class MailServer
     // Storage for the arbitrary number of messages to be stored
     // on the server.
     private HashMap messages;
     private ArrayList list;
     private MailItem item;
      * Construct a mail server.
     public MailServer()
         messages = new HashMap();
         list = new ArrayList();
      * Return the next message for who. Return null if there
      * are none.
      * @param who The user requesting their next message.
     public MailItem getNextMailItem(String who)
          Iterator it = list.iterator();
          while(it.hasNext())
            MailItem item = (MailItem)it.next();
            if(messages.containsKey(who));
                return item;
           else
               return null;
      * Add the given message to the message list.
      * @param item The mail item to be stored on the server.
     public void post(String name, MailItem item)
         if(messages.containsKey(name))
                list = (ArrayList) messages.get(name);
                else {
                    list = new ArrayList();
                    list.add(item);
                    messages.put(name, list);
}[                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       

Answer 1

The way I understand this is that MailItems are stored in per user ArrayLists, and that the ArrayLists are stored in the HashMap, and use the username as a key,
HashMap messages = new HashMap();
//ArrayList userMailItems = new ArrayList(); this should not be declared here, only the messages mapso given a User name, you need to get the list of mail items for that user out of the hashMap, and then return the next MailItem from the list. So given that, you don't even need to Iterate over the list:
public MailItem getNextMailItem(String who)
ArrayList list = (ArrayList)messages.get(who);
if(list == null || list.size() == 0)
return null;
//now we get the next item from the list, we can call remove, since it returns the object we are removing.
MailItem item = (MailItem)list.remove(0);
return item;
}