Dear People, In doing "Objects First with Java Chapter 4 page 90 an Auction program. Even though I have used the bidFor() method my showLots() method indicates "no bids"
below is the output I received, the TryAuction driver, Auction class, Bid class , Lot class, and Person class.
Thank you in advance Stan
// Here is the output that indicates my logic is lacking
//The first lot for sale: bicycle //The second lot for sale: lamp //The third lot for sale: trailer //Lot number: 3 (trailer) already has a bid of: 900460
//1: A bicycle in so so condition // (No bid) //2: A brand new lamp // (No bid) //3: A trailer built in 2001 // (No bid)
package stan_bluej_ch4p90; //Purpose of project: To demonstrate collections of objects //Version: 2001.05.31 //How to start this project: // Create an Auction object. // Enter a few lots via its enterLot method. Only String // descriptions of the lots are required. // Create one or more Person objects to represent bidders. // Show the lots and select one to bid for. // Get the required Lot onto the object bench. // Enter a bid for the lot, passing the Person who is // bidding to the bidFor method.
public class TryAuction { public static void main(String[] args) { //create the auction Auction cityAuction = new Auction();
//create the lots for sale Lot bicycle = new Lot(1,"bicycle"); Lot lamp = new Lot(2, "lamp"); Lot trailer = new Lot(3, "trailer");
//enter the lots into the city Auction cityAuction.enterLot("A bicycle in so so condition"); cityAuction.enterLot("A brand new lamp"); cityAuction.enterLot("A trailer built in 2001");
//show the lots System.out.println(); System.out.println("The first lot for sale: " + bicycle.getDescription()); System.out.println("The second lot for sale: " + lamp.getDescription()); System.out.println("The third lot for sale: " + trailer.getDescription());
//create the people who will bid for the lots Person Steve = new Person("Steve"); Person Maria = new Person("Maria");
//create the people's bids Bid mariaLampBid = new Bid(Maria, 460); Bid steveLampBid = new Bid(Steve, 510);
//create the people's bids Bid mariaBicycleBid = new Bid(Maria, 1460); Bid steveBicycleBid = new Bid(Steve, 1510);
//create the people's bids Bid mariaTrailerBid = new Bid(Maria, 900460); Bid steveTrailerBid = new Bid(Steve, 700510);
//give the bids lamp.bidFor(Maria,460); lamp.bidFor(Steve,510);
package stan_bluej_ch4p90; import java.util.*; /** * A simple model of an auction. * The auction maintains a list of lots of arbitrary length. * @author David J. Barnes and Michael Kolling. * @version 2001.06.08 */ public class Auction { // The list of Lots in this auction. private ArrayList 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(); nextLotNumber = 1; }
/** * Enter a new lot into the auction. * Lots can only by entered into the auction by an * Auction object. * @param description A description of the lot. */ public void enterLot(String description) { lots.add(new Lot(nextLotNumber, description)); nextLotNumber++; }
/** * Show the full list of lot numbers and lot descriptions in * this auction. Include any details of the highest bids. */ public void showLots() { Iterator it = lots.iterator(); while(it.hasNext()) { Lot lot = (Lot) it.next(); System.out.println(lot.getNumber() + ": " + lot.getDescription()); // Include any details of a highest bid. Bid highestBid = lot.getHighestBid(); if(highestBid != null) { System.out.println(" Bid: " + highestBid.getValue()); } else { System.out.println(" (No bid)"); } } }
/** * Return the lot with the given number. Return null * if a lot with this number does not exist. * @param number The number of the lot to return. */ public Lot getLot(int number) { if((number >= 1) && (number < nextLotNumber)) { // The number seems to be reasonable. Lot selectedLot = (Lot) lots.get(number-1); // Include a confidence check to be sure we have the // right lot. if(selectedLot.getNumber() != number) { System.out.println("Internal error: " + "Wrong lot returned. " + "Number: " + number); } return selectedLot; } else { System.out.println("Lot number: " + number + " does not exist."); return null; } } }
package stan_bluej_ch4p90; /** * A class to model an item (or set of items) in an * auction: a lot. * @author David J. Barnes and Michael Kolling. * @version 2001.06.08 */ public class Lot { // A unique identifying number. private final int number; // A description of the lot. private String description; // The current highest bid for this lot. private Bid highestBid;
/** * Construct a Lot, setting its number and description. * @param number The lot number. * @param description A description of this lot. */ public Lot(int number, String description) { this.number = number; this.description = description; }
/** * Attempt to bid for this lot. A successful bid * must have a value higher than any existing bid. * @param bidder Who is bidding. * @param value The value of the bid. */ public void bidFor(Person bidder, long value) { // We trust that lot is genuine. There is nothing to // prevent a spurious lot from being bid for, but it // would not appear in the auction list. if((highestBid == null) || (highestBid.getValue() < value)) { // This bid is the best so far. setHighestBid(new Bid(bidder, value)); } else { System.out.println("Lot number: " + getNumber() + " (" + getDescription() + ")" + " already has a bid of: " + highestBid.getValue()); } }
/** * @return The lot's number. */ public int getNumber() { return number; }
/** * @return The lot's description. */ public String getDescription() { return description; }
/** * @return The highest bid for this lot. This could be null if * there are no current bids. */ public Bid getHighestBid() { return highestBid; }
/** * @param highestBid The new highest bid. */ private void setHighestBid(Bid highestBid) { this.highestBid = highestBid; } }
package stan_bluej_ch4p90; /** * A class that models an auction bid. The bid contains a reference * to the Lot bid for and the user making the bid. * @author David J. Barnes and Michael Kolling. * @version 2001.05.31 */ public class Bid { // The user making the bid. private final Person bidder; // The value of the bid. This could be a large number so // the long type has been used. private final long value;
/** * Create a bid. * @param bidder Who is bidding for the lot. * @param value The value of the bid. */ public Bid(Person bidder, long value) { this.bidder = bidder; this.value = value; }
/** * @return The bidder. */ public Person getBidder() { return bidder; }
/** * @return The value of the bid. */ public long getValue() { return value; } }
package stan_bluej_ch4p90; /** * Maintain details of someone who participates in an auction. * @author David J. Barnes and Michael Kolling. * @version 2001.05.31 */ public class Person { // The name of this user. private final String name;
/** * Create a new user with the given name. * @param name The user's name. */ public Person(String name) { this.name = name; }
/** * @return The user's name. */ public String getName() { return name; } }
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