o1.auctionhouse

The class AuctionHouse represents electronic auction houses. It provides methods for adding auctions and producing statistics about the items being sold, among other things.

This version of class AuctionHouse allows for various ways of selling items: any objects of type ItemForSale may be added to the auction house.

The class Bid represents bids made for items up for auction in an electronic auction house. Each Bid object stores the name of the bidder — that is, the customer who made the bid — as well as the maximum amount the bidder is willing to pay for the item.

A bid object may also be created that has no bidder at all. This is useful, because a Bid object with no bidder can now be used for representing the initial prices of auctions before any genuine bids have been made.

A bid object is immutable after creation.

Each instance of the class DutchAuction represents an item that has been put up for sale in an electronic auction house. More specifically, the item is being sold in a so-called Dutch auction.

Each Dutch auction has a starting price for the item being sold. However, unlike in a typical (“English-style”) auction where the price goes up from the starting price, the price in a Dutch auction goes down until someone decides to purchase the item. Every day, the price of the item is decreased by a certain amount from the previous day’s price, and the first person who decides to buy the item gets it immediately at the current price.

Upon creation, a starting price and a minimum price are set for the auction. Every day, the method advanceOneDay must be called to update the auction status and to decrease the current price if nobody has bought the item yet. The price of the item will never drop below the preset minimum price. After the minimum price is reached, the auction will remain open (at the minimum price) for a further three days. If nobody still buys the item, the auction expires.

To summarize, a Dutch auction is always in one of these four stages:

• Decreasing price: The auction is open and the current price of the auction keeps dropping daily until the minimum price is reached or until someone buys the item.

• Stagnant: The auction is still open but its price no longer decreases, and instead stays at the minimum price.

• Expired: After the price of the auction has been stagnant at the minimum price for over three days (that is, three additional full days after reaching the minimum price), and still nobody has bought the item, the auction expires and is no longer open.

• Bought: As soon as anyone chooses to buy the item, the auction ceases to be open.

Please note that the term “Dutch auction” has various meanings, one of which is used here. The kind of Dutch auctions that this class represents, are not identical to those featured on the trading web site eBay, for instance.

The class EnglishAuction represents “normal”, “English-style” auctions in an electronic auction house. Each auction object represents an auction for a single item that has been put up for sale.

Each English auction has a starting price for the item being sold. No bids lower than the starting price are accepted. The highest bidder wins the item at the end of the auction. If two bidders bid the same amount, the first bidder wins over the later one. Apart from this, the order in which bids are placed is not significant.

Upon creation, a duration (in days) is set for the auction. Every day, the method advanceOneDay must be called to update the auction status. Once the time limit is reached, the auction closes and the highest bid wins. If there were no bids made by this time, the auction closes anyway and is considered “expired”.

In a traditional non-electronic auction, all bidders are physically present and it is very common for the same person to make multiple slightly increased bids during the course of the auction, which only lasts a relatively short time. The bidding system in an electronic “English auction” is different. When bidding, bidders indicate the maximum price that they are willing to pay for the item. Storing the maximum bid amount in the electronic auction house is convenient, as it allows bidders to indicate how far they are willing to go, without having to come back to the auction house service repeatedly to increase their bids.

Even if a bidder later wins the auction, they do not necessarily have to pay the full maximum price indicated when placing the bid. They only need to pay enough to beat the second highest bidder. Consider an example. Say bidder A has bid a maximum of 100 for an item and bidder B has bid 150, and the auction then closes. B wins the item and has to pay a price of 101 for it, just enough to beat A’s 100.

The maximum bid amount of the leading bidder is not publicly displayed. The program is intended to display only the current price of the auction and the minimum amount that new bidders must bid in order to stand any chance of winning. For instance, say bidder A has placed a bid with a limit of 200 for an item, and bidder B has placed a bid with a limit of 300. The current price of the auction is now 201. The minimum amount that new bidders must bid is 202 (good enough to beat 201). B’s limit of 300 will not become apparent to other bidders unless someone bids over 300, thereby becoming the leading bidder. (Not displaying the leading bidder’s limit is a sensible policy. Otherwise, bidders or sellers could raise the price without any intention of actually winning the item.)

See Huuto.Net or eBay for descriptions of similar real-world systems.

This simple class does not support bid cancellations, reserve prices, item buyouts, etc., and does not store any seller information.

Each instance of the class FixedPriceSale represents an item that has been put up for sale in an (imaginary) electronic auction house. Each such item is being sold for a fixed price (as opposed to being auctioned).

Apart from a price, each sale has a duration measured in days. Every day, the method advanceOneDay must be called. If the set number of days is reached without anyone buying the item, the sale expires and the item can no longer be bought.

The class InstantPurchase represents items that have been put up for sale in an electronic auction house in such a way that they may be immediately purchased at any time while the item is open. As soon as anyone purchases the item, the sale is finalized and nobody else can buy the item.

The class ItemForSale represents items that have been put up for sale in an (imaginary) electronic auction house. Items can be sold in various ways (fixed price, auctions, etc.); the concrete subclasses of this class represent those different ways. This abstract class captures some of the common characteristics of all different sales.

This simple implementation does not store any seller information.