Observer Pattern example

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package designpatterns;   /*  * Observer Pattern example  */   class WeatherData {       float temperature;     float humidity;           public float getTemperature(){         return temperature;     }           public float getHumidity() {         return humidity;     }           public void setTemperature(float t) {         temperature = t;     }           public void setHumidity(float h) {         humidity = h;     } }   /*  * The below interface adds functionality to add, remove subscribers/clients  *  to the internal list so that they can be notified whenever the state of  *  the weather changes.  */    interface WeatherNotifier {     public void notify();     public void addListener(Object client);     public void removeListener(Object client); }   /*  * WeatherData after implementing the above interface  */   class WeatherData implements WeatherNotifier {     private List subscribers;     {         subscribers = new ArrayList();     }           public void notify() {         // notify/wake up all the subscribers to update their view with latest state information         Iterator iterator = subscribers.iterator();         while (iterator.hasNext()) {             iterator.next().update();         }     }       @Override        public void addListener(Object client) {         subscribers.add(client);     }           @Override     public void removeListener(Object client) {         subscribers.remove(client);     }      public void setTemperature(float t) {         temperature = t;         dataChanged();     }           public void setHumidity(float h) {         humidity = h;         dataChanged();     }           private void dataChanged() {         notify();     }       public float getTemperature(){         return temperature;     }           public float getHumidity() {         return humidity;     }   }   interface WeatherReader {     public void update(); }   class WeatherClient implements WeatherReader{     WeatherData source;           public void update() {         System.out.println("Temperature is " + source.getTemperature());         System.out.println("Humidity is    " + source.getHumidity());           } }