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Java Observable notifyObservers(Object arg) Method
Description
The Java Observable notifyObservers(Observer o) method 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(Object arg) method
public void notifyObservers(Object arg)
Parameters
org - Any Object
Return Value
NA
Exception
NA
Notifying Observers for a change for a String Value Change Example
The following example shows the usage of java.util.Observable.notifyObservers() method. We've created an ObservedObject class by extending Observable class and then overridden its method setValue() and using notifyObservers() method, the observers are notified. In main class, We've added the observer using addObserver() method and in output, we've printed the updates happening to the value of ObservedObject.
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 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(name+" called with Arguments: "+arg); } }
Output
Let us compile and run the above program, this will produce the following result −
Value changed to new value: New Value Watcher called with Arguments: New Value
Notifying Observers for a change for an Integer Value Change Example
The following example shows the usage of java.util.Observable.notifyObservers(Object) method. We've created an ObservedObject class by extending Observable class and then overridden its method setValue() and using notifyObservers() method, the observers are notified. In main class, We've added the observer using addObserver() method and in output, we've printed the updates happening to the value of ObservedObject.
package com.tutorialspoint; import java.util.Observable; import java.util.Observer; class ObservedObject extends Observable { private Integer watchedValue; public ObservedObject(Integer value) { watchedValue = value; } public void setValue(Integer 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(1); // 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(2); } public void update(Observable obj, Object arg) { System.out.println(name+" called with Arguments: "+arg); } }
Output
Let us compile and run the above program, this will produce the following result −
Value changed to new value: 2 Watcher called with Arguments: 2
Notifying Observers for a change for an Object Value Change Example
The following example shows the usage of java.util.Observable.notifyObservers(Object) method. We've created an ObservedObject class by extending Observable class and then overridden its method setValue() and using notifyObservers() method, the observers are notified. In main class, We've added the observer using addObserver() method and in output, we've printed the updates happening to the value of ObservedObject.
package com.tutorialspoint; import java.util.Observable; import java.util.Observer; class ObservedObject extends Observable { private Student watchedValue; public ObservedObject(Student value) { watchedValue = value; } public void setValue(Student 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(new Student(1, "Julie")); // 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 Student(2, "Robert")); } public void update(Observable obj, Object arg) { System.out.println(name+" called with Arguments: "+arg); } } class Student { int rollNo; String name; Student(int rollNo, String name){ this.rollNo = rollNo; this.name = name; } @Override public String toString() { return "[ " + this.rollNo + ", " + this.name + " ]"; } }
Output
Let us compile and run the above program, this will produce the following result −
Value changed to new value: [ 2, Robert ] Watcher called with Arguments: [ 2, Robert ]
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