Introducing the Observer Design Pattern in Java

Introducing the Observer Design Pattern in Java

The Observer Design Pattern is a popular behavioral design pattern that allows objects to communicate with each other without being tightly coupled. This pattern is particularly useful in situations where changes in one object need to be propagated to multiple other objects.

In this article, we will explore how to implement the Observer Design Pattern in Java, along with some source code examples.

Getting Started

To illustrate the implementation of the Observer Design Pattern, let’s consider a scenario where we have a Subject class that maintains a list of observers. The Subject class provides methods to register, unregister, and notify the observers. Whenever the state of the Subject changes, it will notify all its registered observers.

First, let’s define the Observer interface that our observers will implement:

public interface Observer {
    void update();

Next, let’s create the Subject class:

import java.util.ArrayList;
import java.util.List;

public class Subject {
    private List<Observer> observers = new ArrayList<>();
    public void registerObserver(Observer observer) {
    public void unregisterObserver(Observer observer) {
    public void notifyObservers() {
        for (Observer observer : observers) {
    // Other methods and logic...

Now, let’s create an example ConcreteObserver class that implements the Observer interface:

public class ConcreteObserver implements Observer {
    public void update() {
        System.out.println("Observer notified!");
        // Perform necessary actions...

Finally, let’s put it all together in our Main class:

public class Main {
    public static void main(String[] args) {
        Subject subject = new Subject();
        Observer observer1 = new ConcreteObserver();
        Observer observer2 = new ConcreteObserver();

When we run the Main class, the output will be:

Observer notified!
Observer notified!


The Observer Design Pattern provides a powerful way to implement event-driven architectures and decoupling between objects. By allowing objects to subscribe and receive updates, it promotes flexibility and extensibility in our applications.

In this article, we have explored the implementation of the Observer Design Pattern using Java and provided a simple example showcasing its usage. With this knowledge, you can now apply this pattern to write more maintainable and scalable code.

Remember, design patterns are tools, not solutions. It’s important to understand the problem you are solving and choose the appropriate pattern for your specific needs.

Keep coding and happy designing!

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