Java API Tutorial - Java Observable.countObservers()

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Syntax

Observable.countObservers() has the following syntax.

public int countObservers()

Example

In the following code shows how to use Observable.countObservers() method.

/*  www  .j av  a  2 s .c  o m*/

import java.util.Observable;
import java.util.Observer;

class ObservedObject extends Observable {
   private String watchedValue;
   
   public ObservedObject(String value) {
      watchedValue = value;
   }
   
   public void setValue(String value) {
      if(!watchedValue.equals(value)) {
         System.out.println("Value changed to new value: "+value);
         watchedValue = value;
         
         setChanged();
         notifyObservers(value);
      }
   }
}
class MainObserver implements Observer {

   public void update(Observable obj, Object arg) {
      System.out.println(obj+"called with Arguments: "+arg);
   }
}
public class Main{
   public static void main(String[] args) {
      ObservedObject watched = new ObservedObject("Original Value");

      MainObserver watcher1 = new MainObserver();
      MainObserver watcher2 = new MainObserver();

      watched.addObserver(watcher1);
      watched.addObserver(watcher2);

      int count = watched.countObservers();
      System.out.println(count+" observers listening");

      watched.setValue("New Value");

      watched.deleteObserver(watcher1);
      count = watched.countObservers();
      System.out.println(count+" observers listening");

      watched.setValue("Latest Value");
   }
   
}

The code above generates the following result.

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