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Java.util.Observable.countObservers() Method
Description
The java.util.Observable.countObservers() returns the number of observers of this Observable object.
Declaration
Following is the declaration for java.util.Observable.countObservers() method
public int countObservers()
Parameters
NA
Return Value
This method returns the number of observers of this object.
Exception
NA
Example
The following example shows the usage of java.util.Observable.countObservers() 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(value); } } } 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 watcher1 = new ObservableDemo("Watcher1"); ObservableDemo watcher2 = new ObservableDemo("Watcher2"); // add observer to the watched object watched.addObserver(watcher1); watched.addObserver(watcher2); // count observers int count = watched.countObservers(); System.out.println(count+" observers listening"); // trigger value change watched.setValue("New Value"); // remove first observer watched.deleteObserver(watcher1); count = watched.countObservers(); System.out.println(count+" observers listening"); // trigger value change watched.setValue("Latest Value"); } public void update(Observable obj, Object arg) { System.out.println(name+" called with Arguments: "+arg); } }
Let us compile and run the above program, this will produce the following result −
2 observers listening Value changed to new value: New Value Watcher2 called with Arguments: New Value Watcher1 called with Arguments: New Value 1 observers listening Value changed to new value: Latest Value Watcher2 called with Arguments: Latest Value
java_util_observable.htm
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