/**
     A mailbox contains messages that can be listed, kept or discarded.
  */
public class Mailbox
{
    /**
       Creates Mailbox object.
       @param aPasscode passcode number
       @param aGreeting greeting string
    */
  public Mailbox(String aPasscode, String aGreeting)
    {
      passcode = aPasscode;
      greeting = aGreeting;
      newMessages = new MessageQueue();
      keptMessages = new MessageQueue();
    }
 
    /**
       Check if the passcode is correct.
       @param aPasscode a passcode to check
       @return true if the supplied passcode matches the mailbox passcode
    */
  public boolean checkPasscode(String aPasscode)
    {
      return aPasscode.equals(passcode);
    }
 
    /**
       Add a message to the mailbox.
       @param aMessage the message to be added
    */
  public void addMessage(Message aMessage)
    {
      newMessages.add(aMessage);
    }
 
    /**
       Get the current message.
       @return the current message
    */
  public Message getCurrentMessage()
    {
      if (newMessages.size() > 0)
        return newMessages.getFirst();
      else if (keptMessages.size() > 0)
        return keptMessages.getFirst();
      else
        return null;
    }
 
    /**
       Remove the current message from the mailbox.
       @return the message that has just been removed
    */
  public Message removeCurrentMessage()
    {
      if (newMessages.size() > 0)
        return newMessages.removeFirst();
      else if (keptMessages.size() > 0)
        return keptMessages.removeFirst();
      else
        return null;
    }
 
    /**
       Save the current message
    */
  public void saveCurrentMessage()
    {
      Message m = removeCurrentMessage();
      if (m != null)
        keptMessages.add(m);
    }
 
    /**
       Change mailbox's greeting.
       @param newGreeting the new greeting string
    */
  public void setGreeting(String newGreeting)
    {
      greeting = newGreeting;
    }
 
    /**
       Change mailbox's passcode.
       @param newPasscode the new passcode
    */
  public void setPasscode(String newPasscode)
    {
      passcode = newPasscode;
    }
 
    /**
       Get the mailbox's greeting.
       @return the greeting
    */
  public String getGreeting()
    {
      return greeting;
    }
 
  private MessageQueue newMessages;
  private MessageQueue keptMessages;
  private String greeting;
  private String passcode;
}