Example 2: The Publisher-Subscriber Protocol

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Example 2 The Publisher-Subscriber Protocol

• Have two collaborating participants

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Publisher

• collaboration PublisherSubscriberProtocol
• participant Publisher
• import void changeOp(Object args)
• protected Vector subscribers new
  Vector()
• export void attach(Subscriber subsc)
• subscribers.addElement(subsc)
• export void detach(Subscriber subsc)
• subscribers.removeElement(subsc)
• import-export void changeOp()
• import()
• for (int i 0 i lt subscribers.size()
  i)
• ((Subscriber)subscribers.elementAt(i)
  ).
• newUpdate(this)

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Subscriber

• participant Subscriber
• import void subUpdate(Publisher publ)
• protected Publisher publ
• export void newUpdate(Publisher aPubl)
• publ aPubl
• subUpdate(publ)

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Classes for deployment

• Class Point
• void set()
• class InterestedInPointChange
• void public notifyChange()
• System.out.println("CHANGE ...")

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Deployment 1

• adapter PubSubConn1
• Publisher is played by Point
• changeOp is played by set
• Subscriber is played by InterestedInPointChange
  
• void subUpdate(Publisher publ)
• notifyChange()
• System.out.println(on Point object "
  
• ((Point) publ).toString())

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Deployment 1
Red expected replaced
Blue from adapter
Point
Publisher
changeOp calls newUpdate attach(Subscriber) deta
ch(Subscriber)
set
InterestedInPointChange
Subscriber
subUpdate(Publisher) newUpdate(Publisher)
subUpdate(Publisher) notifyChange()
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Deployment 2

• adapter PubSubConn2
• Publisher is played by TicTacToe
• changeOp is played by startGame, newPlayer,
  putMark, endGame
• Subscriber is played by BoardDisplay,
  StatusDisplay
• void subUpdate(Publisher publ)
• setGame((Game) publ)
• repaint()