Java.util.Observable.notifyObservers() Method

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Description

The java.util.Observable.notifyObservers() method notify all of its observers if the object has changed. This method later calls the clearChanged method to indicate that this object has no longer changed. This method is equivalent to notifyObservers(null).

Declaration

Following is the declaration for java.util.Observable.notifyObservers() method

public void notifyObservers()

Parameters

NA

Return Value

NA

Exception

NA

Example

The following example shows the usage of java.util.Observable.notifyObservers() method.

package com.tutorialspoint;

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 value has changed notify observers
      if(!watchedValue.equals(value)) {
         System.out.println("Value changed to new value: "+value);
         watchedValue = value;

         // mark as value changed
         setChanged();
         // trigger notification
         notifyObservers();
      }
   }
}
public class ObservableDemo implements Observer {
   public String name;
  
   public ObservableDemo(String name) {
      this.name = name;
   }
   
   public static void main(String[] args) {
      
      // create watched and watcher objects
      ObservedObject watched = new ObservedObject("Original Value");
      
      // watcher object listens to object change
      ObservableDemo watcher = new ObservableDemo("Watcher");

      // add observer to the watched object
      watched.addObserver(watcher);
      
      // trigger value change
      watched.setValue("New Value");
   }
      
   public void update(Observable obj, Object arg) {
      System.out.println("Update called");
   }
}

Let us compile and run the above program, this will produce the following result −

Value changed to new value: New Value
Update called