Mediator Design Pattern Tutorial
Welcome to my Mediator Design Pattern Tutorial! The Mediator design pattern is used to handle communication between related objects (Colleagues). All communication is handled by a Mediator Object and the Colleagues don’t need to know anything about each other to work together.
The Gang of Four description: Allows loose coupling by encapsulating the way disparate sets of objects interact and communicate with each other. Allows for the actions of each object set to vary independently of one another.
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Code from the Video
STOCKOFFER.JAVA
public class StockOffer{
private int stockShares = 0;
private String stockSymbol = "";
private int colleagueCode = 0;
public StockOffer(int numOfShares, String stock, int collCode){
stockShares = numOfShares;
stockSymbol = stock;
colleagueCode = collCode;
}
public int getstockShares() { return stockShares; }
public String getStockSymbol() { return stockSymbol; }
public int getCollCode() { return colleagueCode; }
}
COLLEAGUE.JAVA
public abstract class Colleague{
private Mediator mediator;
private int colleagueCode;
public Colleague(Mediator newMediator){
mediator = newMediator;
mediator.addColleague(this);
}
public void saleOffer(String stock, int shares){
mediator.saleOffer(stock, shares, this.colleagueCode);
}
public void buyOffer(String stock, int shares){
mediator.buyOffer(stock, shares, this.colleagueCode);
}
public void setCollCode(int collCode){ colleagueCode = collCode; }
}
GORMANSLACKS.JAVA
public class GormanSlacks extends Colleague{
public GormanSlacks(Mediator newMediator) {
super(newMediator);
System.out.println("Gorman Slacks signed up with the stockexchange\n");
}
}
JTPOORMAN.JAVA
public class JTPoorman extends Colleague{
public JTPoorman(Mediator newMediator) {
super(newMediator);
System.out.println("JT Poorman signed up with the stockexchange\n");
}
}
MEDIATOR.JAVA
public interface Mediator {
public void saleOffer(String stock, int shares, int collCode);
public void buyOffer(String stock, int shares, int collCode);
public void addColleague(Colleague colleague);
}
STOCKMEDIATOR.JAVA
import java.util.ArrayList;
public class StockMediator implements Mediator{
private ArrayList<Colleague> colleagues;
private ArrayList<StockOffer> stockBuyOffers;
private ArrayList<StockOffer> stockSaleOffers;
private int colleagueCodes = 0;
public StockMediator(){
colleagues = new ArrayList<Colleague>();
stockBuyOffers = new ArrayList<StockOffer>();
stockSaleOffers = new ArrayList<StockOffer>();
}
public void addColleague(Colleague newColleague){
colleagues.add(newColleague);
colleagueCodes++;
newColleague.setCollCode(colleagueCodes);
}
public void saleOffer(String stock, int shares, int collCode) {
boolean stockSold = false;
for(StockOffer offer: stockBuyOffers){
if((offer.getStockSymbol() == stock) && (offer.getstockShares() == shares)){
System.out.println(shares + " shares of " + stock +
" sold to colleague code " + offer.getCollCode());
stockBuyOffers.remove(offer);
stockSold = true;
}
if(stockSold){ break; }
}
if(!stockSold) {
System.out.println(shares + " shares of " + stock +
" added to inventory");
StockOffer newOffering = new StockOffer(shares, stock, collCode);
stockSaleOffers.add(newOffering);
}
}
public void buyOffer(String stock, int shares, int collCode) {
boolean stockBought = false;
for(StockOffer offer: stockSaleOffers){
if((offer.getStockSymbol() == stock) && (offer.getstockShares() == shares)){
System.out.println(shares + " shares of " + stock +
" bought by colleague code " + offer.getCollCode());
stockSaleOffers.remove(offer);
stockBought = true;
}
if(stockBought){ break; }
}
if(!stockBought) {
System.out.println(shares + " shares of " + stock +
" added to inventory");
StockOffer newOffering = new StockOffer(shares, stock, collCode);
stockBuyOffers.add(newOffering);
}
}
public void getstockOfferings(){
System.out.println("\nStocks for Sale");
for(StockOffer offer: stockSaleOffers){
System.out.println(offer.getstockShares() + " of " + offer.getStockSymbol());
}
System.out.println("\nStock Buy Offers");
for(StockOffer offer: stockBuyOffers){
System.out.println(offer.getstockShares() + " of " + offer.getStockSymbol());
}
}
}
TESTSTOCKMEDIATOR.JAVA
public class TestStockMediator{
public static void main(String[] args){
StockMediator nyse = new StockMediator();
GormanSlacks broker = new GormanSlacks(nyse);
JTPoorman broker2 = new JTPoorman(nyse);
broker.saleOffer("MSFT", 100);
broker.saleOffer("GOOG", 50);
broker2.buyOffer("MSFT", 100);
broker2.saleOffer("NRG", 10);
broker.buyOffer("NRG", 10);
nyse.getstockOfferings();
}
}
small correction in buyOffer() function.
System.out.println(shares + ” shares of ” + stock +
” bought by colleague code ” + collCode);
collCode instead of offer.getCollCode()
I think you can use both of them 😉
Yes Atul u r right .. because a buyer cannot buy the shares he is selling .. buy share offer operation is intiated by Colleage 2 i.e. JP Morgan!!
@Derek – Good practiccal example great tutorial!!
Thank you 🙂
Hi Derek!
I want to thank you very much for the effort you make preparing these tutorials. There are very few people on the web that are both willing to teach and along with that know what they’re doing. These videos are great supplement to the GOF’s book.
BTW, this is the first video that was really hard to grasp. The reason was the financial theme you’ve chosen to deal with. It took me 5 minutes to understand the pattern, but 20 minutes to get into broker-shares-sale-buy relationship 😀 I’m definitely dumb in finance..
Regards,
Mike
Hi Mike,
Sorry about the weird example. I have been doing my best to avoid weird tutorials like that in the future. I’m happy you were able to understand it though in the end 🙂