In our everyday lives, we are constantly observing and reacting to changes. For example, we watch the weather forecast and decide whether to carry an umbrella, or we get notifications from our favorite news app and then decide whether to read the article. In both cases, we’re responding to events or changes. Similarly, in software development, we have a design pattern called [drumroll] the “Observer Pattern” that allows objects to [drumroll] observe and react to events or changes in other objects. In this post, we will hopefully demystify the observer pattern, breaking it down into simple terms that anyone can understand.

1. Understanding the Basic Concepts

To understand the observer pattern, let’s first familiarize ourselves with two key concepts: the “subject” and the “observer.”

Subject: The subject is the object that holds the data or the state that other objects might be interested in. In our weather forecast example, the subject would be the weather forecast itself.

Observer: The observer is the object that wants to be notified when there’s a change in the subject’s data or state. In the weather forecast example, the observer would be you, waiting for updates on the weather.

2. The Observer Pattern in Action

Now that we have a basic understanding of the subject and observer, let’s see how they interact in the observer pattern:

a) The observer “subscribes” to the subject: When an observer is interested in a subject’s data or state, it subscribes to the subject. This process is similar to subscribing to a newsletter or following a page on social media.

b) The subject maintains a list of observers: The subject keeps track of all the observers that have subscribed to it. This list allows the subject to notify all observers when there’s a change in its data or state.

c) The subject notifies observers when there’s a change: When the subject’s data or state changes, it goes through its list of observers and notifies them about the change. In our weather forecast example, this is like receiving a notification about an updated forecast.

d) The observer “unsubscribes” from the subject: When an observer is no longer interested in a subject’s data or state, it can unsubscribe from the subject. This is like unsubscribing from a newsletter or unfollowing a page on social media.

3. Benefits of the Observer Pattern

The observer pattern offers several benefits, including:

a) Loose coupling: The subject and observers are not tightly linked, which means that they can evolve independently. This loose coupling makes it easier to maintain and modify the code as needed.

b) Scalability: Since the subject doesn’t need to know the details about each observer, it’s easy to add or remove observers without affecting the subject’s code. This makes the system more scalable.

c) Better organization: By separating the responsibilities of the subject and observers, the observer pattern promotes better organization of the code, making it easier to understand and maintain.

The observer design pattern is an elegant design approach that fosters organized, scalable, and easy-to-maintain software systems. Streamlining the interactions between subjects and observers enables efficient communication and adaptability in a constantly changing environment.