Class and Object

/**
 * A simple model of an auction.
 *
 * @author (your name)
 * @version (a version number or a date)
 */

import java.util.ArrayList;
import java.util.Iterator;
public class Auction
{
   // The List of Lots in this auction.
   private ArrayList<Lot> lots;
   // The number that will be given to the next lot entered
   // into this auction
   private int nextLotNumber;
   /**
    * Create a new auction
    */
   public Auction()
   {
     lots = new ArrayList<Lot>();
     nextLotNumber = 1;
   }
   /**
    * Enter a new lot into the auction.
    * @param description A description of the lot.
    */
   public void enterLot(String description)
   {
     lots.add(new Lot(nextLotNumber, description));
     nextLotNumber++;
   }
   /***
    * Show the full list of lots in this auction.
    */
   public void showLots()
   {
     for(Lot lot : lots){
       System.out.println(lot.toString());
     }
   }
   /**
    * Bid for a lot.
    * A message indicating whether the bid is succesful or not is printed.
    * @param number The lot number being bid for.
    * @param bidder The person bidding for the lot.
    * param value The value of the bid.
    */
   public void bidFor(int lotNumber, Person bidder, long value)
   {
     Lot selectedLot = getLot(lotNumber);
     if(selectedLot!=null){
       boolean successful = selectedLot.bidFor(new Bid(bidder,value));
       if (successful) {
         System.out.println("The bid for lot number " + lotNumber +
         " was successful.");
       }
       else {
         //Report which bid is higher.
         Bid highestBid = selectedLot.getHighestBid();
         System.out.println("Lot number: " + lotNumber +
         " already has a bid of: " + highestBid.getValue());
       }
     }
   }
   /**
    * Return a list of the unsold lots.
    */
   public void close()
   {
     System.out.println("The auction is closed.");
     for(Lot lot : lots) {
       System.out.println(lot.getNumber() + ": " +lot.getDescription());
       Bid bid = lot.getHighestBid();
       if (bid==null){
         System.out.println("(No Bids for this lot.)");
       }
       else {
         System.out.println( "sold to " +
         bid.getBidder().getName() + " for "
         + bid.getValue());
     }
   }
 }
   /**
    * Return the lot with the given number.
    * Return null if a lot with this number does not exist.
    * @param lotNumber The number of the lot to return.
    */
    public Lot getLot(int lotNumber)
    {
        if((lotNumber >= 1) && (lotNumber < nextLotNumber)) {
        // The number seems to be reasonable.
        Lot selectedLot = lots.get(lotNumber - 1);
        // Include a confidence check to be sure we have the right lot.
        if(selectedLot.getNumber() != lotNumber) {
          System.out.println("Internal error: lot number " +
          selectedLot.getNumber() + " was returned instead of " +
          lotNumber);
          // Don't return invalid lot.
          selectedLot = null;
         }
         return selectedLot;
        }
        else {
        System.out.println("lot number: " + lotNumber + " does not exist.");
        return null;
        }
     }
}