Adapter Pattern

What is the Adapter Pattern? #

• It is primarily used when converting the interface of one class to another interface that you want to use.
• It's a pattern that allows classes with incompatible interfaces, which normally cannot be used together, to be connected and used through an association.

Advantages #

1. Allows unrelated interfaces to be used together
2. Easier program inspection
3. Increased class reusability, etc.

Java Adapter Pattern - Structure Explanation #

It can be represented by the following diagram.

Below is the AudioPlayer interface and the MP3 class that implements the AudioPlayer interface. #

AudioPlayer.java

public interface AudioPlayer {
  void play(String filename);
}

MP3.java

public class MP3 implements AutoPlayer {

  @Override
  void play(String filename) {
    System.out.println("Playing MP3 FILE :" + filename);
  }
}

Below is the VideoPlayer interface and the MP4, MKV classes that implement the VideoPlayer interface. #

VideoPlayer.java

public interface VideoPlayer {

  void play(String filename);
}

MP4.java

public class MP3 implements VideoPlayer{
   
   @Override
   void play(String filename){
      System.out.println("Playing MP4 File ▶ : "filename);
   }
   
}

MKV.java

public class MKV implements VideoPlayer{
   
   @Override
   void play(String filename){
      System.out.println("Playing MKV File ▶ : "filename);
   }
   
}

Below is the FormatAdapter Class, which helps make VideoPlayer formats usable with AudioPlayer formats. The FormatAdapter class inherits the AudioPlayer interface and uses VideoPlayer as a member variable. It receives a VideoPlayer as a constructor argument and uses that video format.

FormatAdapter.java

public class FormatAdapter implements AudioPlayer{
   
   private VideoPlayer media;
   
   public FormatAdapter(VideoPlayer video){
      this.media = video;
   }
   
   @Override
   void play(String filename){
      System.out.println("Using Adapter : ");
      media.playFile(filename);
   }
   
}

The Main Class below is an example of using the Adapter Pattern. An mp3Player object was created as an AudioPlayer reference variable with an MP3 instance. By using an adapter with an MP4 instance, MP4 can also be used with mp3Player.

Main.java

public class Main{

   public static void main(String[] args){
   
   AudioPlayer mp3Player = new MP3();
   mp3Player.play("file.mp3");
   
   mp3Player = new FormatAdapter(new MP4());
   mp3Player.play("file.mp4");
   
   mp3Player = new FormatAdapter(new MKV());
   mp3Player.play("file.mkv");
   
   }
   
}

Running the code above will produce the following output:

> Playing MP3 File ♪ : file.mp3
> Using Adapter : Playing MP4 File ▶ : file.mp4
> Using Adapter : Playing MKV File ▶ : file.mkv

Thus, through the Adapter Pattern, mp3Player can also play video format files.