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Java Observable addObserver() Method with Example

Observable Class addObserver() method: Here, we are going to learn about the addObserver() method of Observable Class with its syntax and example.
Submitted by Preeti Jain, on March 02, 2020

Observable Class addObserver() method

• addObserver() method is available in java.util package.
• addObserver() method is used to insert the given observer (obs) to the bundles of observers for this Observable object.
• addObserver() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.
• addObserver() method may throw an exception at the time of adding an observer.

Syntax:

    protected void addObserver(Observer obs);

Parameter(s):

• Observer obs – represents the observer object to be inserted.

Return value:

The return type of the method is void, it returns nothing.

Example:

// Java program to demonstrate the example 
// of void addObserver(Observer obs) method of Observable

import java.util.*;

// Implement Observers class 
class Observers implements Observer {
    public void update(Observable obj, Object ob) {
        System.out.println("Obs is added");
    }
}

// Implement Observed Class
class Observed extends Observable {
    void added() {
        setChanged();
        notifyObservers();
    }
}

public class Main {
    // Implement Main Method
    public static void main(String args[]) {
        Observed observed = new Observed();
        Observers obs = new Observers();
        observed.addObserver(obs);
        observed.added();
    }
}

Output

Obs is added