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Observer.java
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Observer.java
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import java.util.ArrayList;
import java.util.List;
/**
* Observer Design Pattern Example
*
*/
public abstract class Observer {
protected Subject mysub;
public abstract void update();
}
class WebServer extends Observer {
public WebServer (Subject sub) {
this.mysub = sub;
this.mysub.addNewObserver(this);
}
@Override
public void update() {
System.out.println("The web server has been updated!");
}
}
class MailServer extends Observer {
public MailServer(Subject sub) {
this.mysub = sub;
this.mysub.addNewObserver(this);
}
@Override
public void update() {
System.out.println("The mail server has been updated!");
}
}
class DNS extends Observer {
public DNS(Subject sub) {
this.mysub = sub;
this.mysub.addNewObserver(this);
}
@Override
public void update() {
System.out.println("The domain name server has been updated!");
}
}
class Subject {
private List<Observer> obsList = new ArrayList<Observer>();
private int state;
public int getState() {
return this.state;
}
public void setState(int state) {
this.state = state;
notifyAllObservers();
}
public void addNewObserver(Observer observer) {
obsList.add(observer);
}
public void notifyAllObservers() {
for(Observer o : obsList) {
o.update();
}
}
}