What is an Adapter Design Pattern?

1.	What is an Adapter Design Pattern?
Answer» The adapter design pattern falls under the CATEGORY of a structural design pattern that lets incompatible objects collaborate. It acts as a wrapper between 2 different objects. The adapter catches the call for one object and transforms them to be recognizable by the SECOND object. Let us understand this with the help of an example of a USB to Ethernet adapter that is used when we have an ethernet interface at one end and the USB interface on the other end. The USB and ethernet are incompatible with each other which is why we require an adapter. The adapter CLASS has a Client class that expects some object type and it has an Adaptee class that offers the same feature but by exposing a different interface. Now to make these both communicate, we have an Adapter class. The client requests the Adapter by using the target interface. The Adapter class translates the request using the Adaptee Interface on the adaptee. The Client receives the results UNAWARE of the adapter’s role. This has been described in the class diagram as shown below: Class Diagram: Let us consider that we have a MediaPlayer Interface which is implemented by the AudioPlayer class. The AudioPlayer can play mp3 format by default. Consider another interface AdvancedPlayer that is being implemented by MP4Player class that plays mp4 formats and WAVPlayer that plays wav formats. If we want to make AudioPlayer class play other formats, then we make use of the MediaAdapter class that implements the MediaPlayer Interface and uses the AdvancedPlayer objects for playing the required format. The code implementation of this SCENARIO is as follows: //MediaPlayer.javapublic interface MediaPlayer { public void play(String format, String file);}//AdvancedPlayer.javapublic interface AdvancedPlayer { public void playMp4(String file); public void playWav(String file);}//Mp4Player.javapublic class Mp4Player implements AdvancedPlayer{ @Override public void playMp4(String file) { System.out.println("MP4 File "+ file + " Playing...."); } @Override public void playWav(String file) { //do nothing }}//WAVPlayer.javapublic class WAVPlayer implements AdvancedPlayer{ @Override public void playMp4(String file) { //do nothing } @Override public void playWav(String file) { System.out.println("WAV File "+ file + " Playing...."); }}//MediaAdapter.javapublic class MediaAdapter implements MediaPlayer { AdvancedPlayer advancedPlayer; public MediaAdapter(String format){ if(format.equalsIgnoreCase("mp4") ){ advancedPlayer = new Mp4Player(); }else if(format.equalsIgnoreCase("wav") ){ advancedPlayer = new WAVPlayer(); } } @Override public void play(String format, String file) { if(format.equalsIgnoreCase("mp4")){ advancedPlayer.playMp4(file); } else if(format.equalsIgnoreCase("wav")){ advancedPlayer.playWav(file); } }}//AudioPlayer.javapublic class AudioPlayer implements MediaPlayer { MediaAdapter mediaAdapter; @Override public void play(String format, String file) { //inbuilt support to play mp3 music files if(format.equalsIgnoreCase("mp3")){ System.out.println("MP3 file " + file +" Playing..."); } //Make use of Adapter to support different formats else if(format.equalsIgnoreCase("wav") \|\| format.equalsIgnoreCase("mp4")){ mediaAdapter = new MediaAdapter(format); mediaAdapter.play(format, file); } else{ System.out.println("Format not supported"); } } }//Driver.javapublic class Driver { public static void main(String[] args) { AudioPlayer audioPlayer = new AudioPlayer(); audioPlayer.play("mp3", "music1.mp3"); audioPlayer.play("wav", "music2.wav"); audioPlayer.play("mp4", "music3.mp4"); audioPlayer.play("avi", "music4.avi"); }} The output of this code would be: MP3 file music1.mp3 Playing...WAV File music2.wav Playing...MP4 File music3.mp4 Playing...Format not supported

Answer»

The adapter design pattern falls under the CATEGORY of a structural design pattern that lets incompatible objects collaborate. It acts as a wrapper between 2 different objects. The adapter catches the call for one object and transforms them to be recognizable by the SECOND object.

Let us understand this with the help of an example of a USB to Ethernet adapter that is used when we have an ethernet interface at one end and the USB interface on the other end. The USB and ethernet are incompatible with each other which is why we require an adapter. The adapter CLASS has a Client class that expects some object type and it has an Adaptee class that offers the same feature but by exposing a different interface. Now to make these both communicate, we have an Adapter class. The client requests the Adapter by using the target interface. The Adapter class translates the request using the Adaptee Interface on the adaptee. The Client receives the results UNAWARE of the adapter’s role. This has been described in the class diagram as shown below:

Class Diagram:

Let us consider that we have a MediaPlayer Interface which is implemented by the AudioPlayer class. The AudioPlayer can play mp3 format by default. Consider another interface AdvancedPlayer that is being implemented by MP4Player class that plays mp4 formats and WAVPlayer that plays wav formats. If we want to make AudioPlayer class play other formats, then we make use of the MediaAdapter class that implements the MediaPlayer Interface and uses the AdvancedPlayer objects for playing the required format. The code implementation of this SCENARIO is as follows:

//MediaPlayer.javapublic interface MediaPlayer { public void play(String format, String file);}//AdvancedPlayer.javapublic interface AdvancedPlayer { public void playMp4(String file); public void playWav(String file);}//Mp4Player.javapublic class Mp4Player implements AdvancedPlayer{ @Override public void playMp4(String file) { System.out.println("MP4 File "+ file + " Playing...."); } @Override public void playWav(String file) { //do nothing }}//WAVPlayer.javapublic class WAVPlayer implements AdvancedPlayer{ @Override public void playMp4(String file) { //do nothing } @Override public void playWav(String file) { System.out.println("WAV File "+ file + " Playing...."); }}//MediaAdapter.javapublic class MediaAdapter implements MediaPlayer { AdvancedPlayer advancedPlayer; public MediaAdapter(String format){ if(format.equalsIgnoreCase("mp4") ){ advancedPlayer = new Mp4Player(); }else if(format.equalsIgnoreCase("wav") ){ advancedPlayer = new WAVPlayer(); } } @Override public void play(String format, String file) { if(format.equalsIgnoreCase("mp4")){ advancedPlayer.playMp4(file); } else if(format.equalsIgnoreCase("wav")){ advancedPlayer.playWav(file); } }}//AudioPlayer.javapublic class AudioPlayer implements MediaPlayer { MediaAdapter mediaAdapter; @Override public void play(String format, String file) { //inbuilt support to play mp3 music files if(format.equalsIgnoreCase("mp3")){ System.out.println("MP3 file " + file +" Playing..."); } //Make use of Adapter to support different formats else if(format.equalsIgnoreCase("wav") || format.equalsIgnoreCase("mp4")){ mediaAdapter = new MediaAdapter(format); mediaAdapter.play(format, file); } else{ System.out.println("Format not supported"); } } }//Driver.javapublic class Driver { public static void main(String[] args) { AudioPlayer audioPlayer = new AudioPlayer(); audioPlayer.play("mp3", "music1.mp3"); audioPlayer.play("wav", "music2.wav"); audioPlayer.play("mp4", "music3.mp4"); audioPlayer.play("avi", "music4.avi"); }}

The output of this code would be:

MP3 file music1.mp3 Playing...WAV File music2.wav Playing...MP4 File music3.mp4 Playing...Format not supported

What is an Adapter Design Pattern?

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