Microsoft Interview for Intern

FbGoo

Design a stock market system

爸爸回来了

Can make use of Observer Design Pattern. 5 a3 U. d4 t8 u% B7 @' p
Here is a simple implementation of the Publisher/Subscriber model for StockMarket. As and when interviewer pose with some more questions, we can add on to it.
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Publisher Interface:

public interface Publisher {
  public void setStockValue(int value);
  public void registerObserver(Observer observer);
( B2 {4 ?. }9 M% e% l) S1 r9 A  public void unRegisterObserver(Observer observer);
  public void notifyAllObservers();
}

Subscriber(Observer) Interface:

public interface Observer {
   public void update(int newValue);
* T3 H/ R! G  k' j% K4 c   public void display();
9 t: K! |+ d# g7 Q8 ~   public void unSubscribe();
}

StockMarket Class which implements the Publisher interface:

public class StockMarket : Publisher {
  Set<Observer> observers;
  int newValue;
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. P. A+ k6 f0 E, b' K1 V  public StockMarket() {
	observers = new HashSet<Observer>();
) {; ]! m5 R" V: V4 e	newValue = 0;
" }; L5 v: u* H# |  }  
% h# f, `7 @7 c2 q* t4 x/ d  
  public void setStockValue(int value){
" _1 i- q0 `6 ?$ K    newValue = value;
  }
  
! Y9 d0 m& L, w0 w  public void registerObserver(Observer observer){
$ n% w9 i7 w- }7 g. K* P- W4 O    observers.add(observer);
  }

; ~3 f, d. H; u$ z0 ^3 Q  public void unRegisterObserver(Observer observer){
2 U4 N( g+ k* x1 k0 @! L    if(observer != null && observer instanceof Observer){
0 n+ _, p! N* o& ~" X6 }	    observers.remove(observer);
	}
  }

  public void notifyAllObservers(){
	Iterator<Observer> observerIterator = observers.iterator();
' x& ~  H, `! @, J+ C	while(observerIterator.hasNext()){
		Observer observer = observerIterator.next();
- `2 Y( U# G( M! u: Y		observer.update(this, null);
	}
4 {! x0 Q7 ^" P: ~. M% R( q( E  }
5 Z7 k( b! W, V4 m}

As a sample i will implement the PayPalStock which implements the Observer Interface. This inturn maintains a reference to the Publisher.

public class PayPalStock : Observer {
   Publisher stockMarket;
& u( X# p1 Y$ o3 `) ?5 [   int latestValue;
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! I6 E# z: H( D9 {0 S: Z" W   public PayPalStock (Publisher subject){
   	latestValue = 0;
* \- v- R4 c, m7 Y3 k/ F    stockMarket = subject;
    stockMarket.registerObserver(this); // Self-Registering to the Publisher
   }

   public void update(int newValue){
    latestValue = newValue;
    display();
& U- J8 E9 r( ?! D- J$ D   }
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6 `1 P/ r" e1 a4 F* Q! s$ S+ X- z2 N6 Z2 M   public void display(){
     System.out.println("Latest Stock Price = " + latestValue);
   }
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' j! A3 y; j+ n% M/ p   public void unSubscribe(){
     stockMarket.unRegisterObserver(this);
   }
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A more detailed design can be looked up at: http://read.pudn.com/downloads152/doc/663610/Software%20Design.pdf

妖精的尾巴

A market is a place where buy and sell happens real-time or in a batch. depending on the service... The code above won't cut....