Interfaces and Multiple Inheritance

Understanding Interfaces with a Simple Example

Table of contents

1. Why Interfaces?

Why Interfaces? (Motivation behind)

Imagine you’re building a playlist app. Different music services (like Spotify, Apple Music, etc.) have different ways to play songs, but you want your app to work with all of them. You need a way to define what it means to “play” a song, regardless of the music service being used. This is where an interface comes in.

How and Where:

An interface in Java is like a contract that says, “Any class that implements this interface must have these specific methods.” It’s like setting rules everyone has to follow to play a song.

Here’s a simple interface example:

// Topic: Define an Interface
interface MusicPlayer {
    void playSong(String songName);
}

Now, any music service that wants to be part of your app must implement this interface:

// Topic: Implement the Interface
class SpotifyPlayer implements MusicPlayer {
    public void playSong(String songName) {
        System.out.println("Playing " + songName + " on Spotify.");
    }
}

class AppleMusicPlayer implements MusicPlayer {
    public void playSong(String songName) {
        System.out.println("Playing " + songName + " on Apple Music.");
    }
}

When:

Use an interface when you want to define a set of actions that different classes can perform, even if they do it in their own way.

How to decide:

If you find yourself thinking, “I want different objects to do the same thing but in their own unique way,” an interface might be the right tool.

Relating to APIs:

Think of an interface like an API. Just like how different apps use an API to interact with a service without knowing its internal workings, your code uses an interface to interact with different classes without worrying about how they perform their tasks. The interface/API defines “what” should happen, while the actual class decides “how” it happens.

Experiments

Experiment with Interfaces here.

Practice Exercises

Practice Interfaces with exercises.