Observer Pattern

Observer Pattern:-

Here in this pattern, if one object changes it state then all its dependents are notified and updated automatically on each event.

Sample:

MyObservable:

import java.io.File;

import java.util.Observable;

public class MyObservable extends Observable {

      public void findFiles(File file) {

            if (file != null) {

                  if (file.isFile()) {

                        setChanged();

                        notifyObservers(file.getAbsolutePath());

                  } else {

                        File[] fileList = file.listFiles();

                        if (fileList != null) {

                              for (File f : fileList) {

                                    findFiles(f);

                              }

                        }

                  }

            }

      }

}

MyObserver:

import java.util.Observable;

import java.util.Observer; 

public class MyObserver implements Observer {

      public void update(Observable obj, Object arg) {

            System.out.println("\nReceived Response: " + arg);

      }

}

ObserverPattern:

import java.io.File;

public class ObserverPattern {

      public static void main(String[] args) {

        final MyObservable observable = new MyObservable();

        final MyObserver observer = new MyObserver();

       

        observable.addObserver(observer);

        observable.findFiles(new File("."));

      }

}