The adapter pattern allows classes with incompatible interfaces to work together by providing wrapper classes that translate requests from one interface to calls that the wrapped class understands. An adapter class aggregates the adapted class and provides a common interface to the client. This allows code using the adapter to call its methods without knowledge of the adapted class's specific interface. For example, an adapter class could implement a media player interface to translate calls to different media file types like MP4 and VLC.

1. ADAPTER PATTERN
BY
IBAD –UR-REHMAN

2. Structure Pattern
Structural design patterns are concerned with
how classes and objects can be composed, to form
larger structures.
The structural design patterns simplifies the
structure by identifying the relationships.
These patterns focus on, how the classes inherit
from each other and how they are composed from
other classes.

3. Types of Structure Pattern
Different categories
Adapter
Bridge
Composite
Decorator
Façade
Flyweight
Proxy

4. Adapter Pattern
Allow an application to use external
functionality in a retarget able manner
Adapters are used to enable objects with
different interfaces to communicate with
each other.
They are also termed as wrappers.

5. Design Summary
Write the application against the abstract
version of external class, introduce the sub-
class that aggregate the external class

6. UML
Client
Target
Request( )
Adaptee
SpecificRequest( )
Adapter
Request( )
Adaptee->SpecificRequest( )
adaptee

7. Real-Life Application
Create interfaces for MediaPlayer and MediaPackage.
MediaPlayer.java
public interface MediaPlayer {
public void play(String fileName);
}
MediaPackage.java
public interface MediaPackage {
public void playFile(String fileName);
}

8. Real-Life Application (cont.)
Create concrete classes implementing the MediaPlayer interface
public class MP3 implements MediaPlayer {
@Override
public void play(String filename) {
System.out.println("Playing MP3 File " + filename);
}

9. Real-Life Application (cont.)
Create concrete classes implementing the MediaPackage
interface.
VlcPlayer.java
public class VlcPlayer implements MediaPackage{
@Override
public void playFile(String fileName) {
System.out.println("Playing vlc file. Name: "+ fileName);
}
}

10. Real-Life Application (cont.)
Mp4Player.java
public class Mp4Player implements MediaPackage {
@Override
public void playFile(String fileName) {
System.out.println("Playing mp4 file. Name: "+
fileName);
}
}

11. Real-Life Application (cont.)
Create adapter class implementing the MediaPlayer
interface.
public class FormatAdapter implements MediaPlayer {
private MediaPackage media;
public FormatAdapter(MediaPackage m) {
media = m;
}
@Override
public void play(String filename) {
System.out.print("Using Adapter --> ");
media.playFile(filename);
}

12. Real-Life Application (cont.)
public class Main { public static void main(String[]
args) {
MediaPlayer player = new MP3();
player.play("file.mp3");
player = new FormatAdapter(new MP4());
player.play("file.mp4");
player = new FormatAdapter(new VLC());
player.play("file.avi");
}
}

14. Purpose & Usage
An adapter class provides the default
implementation of all methods in an event
listener interface. Adapter classes are very
useful when you want to process only few
of the events that are handled by a particular
event listener interface. You can define a
new class by extending one of the adapter
classes and implement only those events
relevant to you.

15. Why in Structural Pattern.
Adapter pattern works as a bridge between
two incompatible interfaces. This type of
design pattern comes under structural
pattern as this pattern combines the
capability of two independent interfaces.
This pattern involves a single class which is
responsible to join functionalities of
independent or incompatible interfaces