Adapter design pattern example javatpoint

• Adapter inherits both from Target and Adaptee .
• The client invokes requiredMethod() on an instance of Adapter which is also an instance of Target by virtue of being its subclass.
• Adapter overrides the requiredMethod() of Target and in its implementation internally calls Adaptee ’s targetMethod() .
• Thus, Client is able to use targetMethod() functionality from Adaptee through the Adapter without change of the interface which still remains Target for the client.

• Adapter extends Target .
• Adapter also keeps an instance of Adaptee as a class variable.
• When Client calls -
  • The Client invokes requiredMethod() on an instance of Adapter which is also an instance of Target by virtue of being its subclass.
  • Adapter overrides the requiredMethod() of Target and in its implementation internally calls its class variable adaptee's targetMethod() .

  

  Note - In the class diagram above I have focussed on showing the primary participating classes & their methods. I have not included the method parameters and constructors in the same.

  Code for the classes drawn in Java Class Diagram

  Code for classes shown in Java Class Diagram

  //FileCommiter.java import java.io.File; public class FileCommiter < String diskLocation; public FileCommiter()< //default constructor >public FileCommiter(String diskLocation) < this.diskLocation=diskLocation; >public void saveFile(File file) < //Logic for saving the file at the diskLocation goes here >> //FileEmailer.java import java.io.File; public class FileEmailer < public String emailAddress; public FileEmailer(String emailAddress)< this.emailAddress=emailAddress; >public void emailFile(File file) < //Logic for emailing the file goes here >> //FileEmailerAdapter.java import java.io.File; public class FileEmailerAdapter extends FileCommiter < public FileEmailer fileEmailer; public FileEmailerAdapter(FileEmailer fileEmailer)< this.fileEmailer=fileEmailer; >public void saveFile (File file) < this.fileEmailer.emailFile(file); >> //Client.java import java.io.File; public class Client < public static void main(String args[])< File file=new File(args[0]); FileCommiter fileCommiter=new FileCommiter("C:\\"); fileCommiter.saveFile(file);//This will save the file on the disk location C: drive //Now we want to email with the same Target class FileCommiter fileCommiter=new FileEmailerAdapter(new FileEmailer("abcd@javabrahman.com")); fileCommiter.saveFile(file);//This will email the file to abcd@javabrahman.com >>

  • FileCommiter class has the responsibility of committing files to the disk location. The disk location is set via a constructor parameter.
  • FileEmailer class has the responsibility of emailing files to the email address. The email address is set via a constructor parameter
  • FileEmailerAdapter extends FileCommiter .
  • FileEmailerAdapter has a class variable of type FileEmailer called fileEmailer . This fileEmailer class variable is set via a constructor parameter.
  • Client first creates a new java.io.File instance based on command line argument passed to it.
  • Client then creates a FileCommiter instance with a disk location value of C drive and saves the file instance it created using the saveFile() method.
  • Next the Client creates a FileEmailerAdapter instance using a FileEmailer with an email address.
  • Client then invokes the saveFileMethod() on fileEmailAdapter . This time instead of commiting the file on the disk location FileEmailerAdapter internally routes the request to emailFile() method of class variable adaptee .
  • Thus, with the same interface of FileCommiter , Client is now able to email a file as well.This is adapter pattern.

  Summary This concludes the article on adapter design pattern where we saw what is adapter pattern. Then we learned about its two variants - Class and Object Adapters and saw class diagram of each. Then we saw a Java Implementation of a FileEmailer Adapter through code and then its explanation.