1  import java.util.ArrayList;

  2  

  3  /**

  4     A system of voice mail boxes.

  5  */

  6  public class MailSystem

  7  {

  8     /**

  9        Constructs a mail system with a given number of mailboxes

 10        @param mailboxCount the number of mailboxes

 11     */

 12     public MailSystem(int mailboxCount)

 13     {

 14        mailboxes = new ArrayList<>();

 15  

 16        // Initialize mail boxes.

 17  

 18        for (int i = 0; i < mailboxCount; i++)

 19        {

 20           String passcode = "" + (i + 1);

 21           String greeting = "You have reached mailbox " + (i + 1)

 22                 + ". \nPlease leave a message now.";

 23           mailboxes.add(new Mailbox(passcode, greeting));

 24        }

 25     }

 26  

 27     /**

 28        Locate a mailbox.

 29        @param ext the extension number

 30        @return the mailbox or null if not found

 31     */

 32     public Mailbox findMailbox(String ext)

 33     {

 34        int i = Integer.parseInt(ext);

 35        if (1 <= i && i <= mailboxes.size())

 36           return  mailboxes.get(i - 1);

 37        else return null;

 38     }

 39  

 40     private ArrayList<Mailbox> mailboxes;

 41  }