SA03.6 - Adapter Pattern

designpatterns/structural

It acts like a translator between two mismatched systems.

The Adapter Pattern is a structural design pattern that allows two incompatible interfaces to work together by wrapping one inside another — it converts the interface of a class into one the client expects.

Structure

Analogy

When to Use

• When you need to reuse an existing class but its interface doesn’t match what your system expects
• When you want to decouple systems by introducing a middle translation layer
• When integrating third-party libraries that can’t be modified

Code Example

// Target interface
interface MediaPlayer {
    void play(String audioType, String fileName);
}
 
// Adaptee interface
interface AdvancedMediaPlayer {
    void playVlc(String fileName);
    void playMp4(String fileName);
}
 
// Concrete Adaptees
class VlcPlayer implements AdvancedMediaPlayer {
    public void playVlc(String fileName) {
        System.out.println("Playing vlc file: " + fileName);
    }
    public void playMp4(String fileName) {
        // Do nothing
    }
}
 
class Mp4Player implements AdvancedMediaPlayer {
    public void playVlc(String fileName) {
        // Do nothing
    }
    public void playMp4(String fileName) {
        System.out.println("Playing mp4 file: " + fileName);
    }
}
 
// Adapter
class MediaAdapter implements MediaPlayer {
    AdvancedMediaPlayer advancedMusicPlayer;
 
    public MediaAdapter(String audioType) {
        if (audioType.equalsIgnoreCase("vlc")) {
            advancedMusicPlayer = new VlcPlayer();
        } else if (audioType.equalsIgnoreCase("mp4")) {
            advancedMusicPlayer = new Mp4Player();
        }
    }
 
    public void play(String audioType, String fileName) {
        if (audioType.equalsIgnoreCase("vlc")) {
            advancedMusicPlayer.playVlc(fileName);
        } else if (audioType.equalsIgnoreCase("mp4")) {
            advancedMusicPlayer.playMp4(fileName);
        }
    }
}
 
// Concrete MediaPlayer
class AudioPlayer implements MediaPlayer {
    MediaAdapter mediaAdapter;
 
    public void play(String audioType, String fileName) {
        if (audioType.equalsIgnoreCase("mp3")) {
            System.out.println("Playing mp3 file: " + fileName);
        } else if (audioType.equalsIgnoreCase("vlc") || audioType.equalsIgnoreCase("mp4")) {
            mediaAdapter = new MediaAdapter(audioType);
            mediaAdapter.play(audioType, fileName);
        } else {
            System.out.println("Invalid media. " + audioType + " format not supported.");
        }
    }
}
 
// Main Demo
public class AdapterPatternDemo {
    public static void main(String[] args) {
        AudioPlayer audioPlayer = new AudioPlayer();
 
        audioPlayer.play("mp3", "song.mp3");
        audioPlayer.play("mp4", "video.mp4");
        audioPlayer.play("vlc", "movie.vlc");
        audioPlayer.play("avi", "clip.avi");
    }
}