Friday, September 27

Java :: Adaptor Design pattern.

                                                          Adaptor Design pattern.

What is Adaptor

Adaptor is used to make tow parties talk with each otherwise could not talk as their communication channel is not compatible with each other

For Example :

Adaptor for a mobile charger : Mobile can not be directly plugged in to electric socket to charge it . It between it requires an adaptor to to get connected. Adaptor converts 220V from electric socket to 9V what Mobile is made to accept .

An interpreter between two people talking two different languages unknown to each other. Interpreter acts as adaptor here.

Let me take you through java code How we can easily implement and use this pattern in java.

A class A has a method m which takes two parameters String ,String But client who wants to invoke that method does not have a pair of strings but has a Map . So how will they talk . We will insert one more class between then which will act as adaptor . It will take input from client ,will covert the Map parameters in String,String pair combinations and will call the class A method m . Thus client and service class A are not talking with each other directly and Adaptor is making their communication possible.

Here is example with java code . I have written are steps in system.out.println statements in methods. Executing then will print all logical steps on console. So copy this code and Execute .


This is the client class which has a Map with it But want to invoke execute of service class which expects a pair of String. So it can't call Service class directly Instead it invokes execute method in Adaptor class

package adaptor;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

public class Client {

     * @param args
    public static void main(String[] args) {

        IAdaptor adaptor = new Adaptor();
        Map map = new LinkedHashMap();
        map.put("Client", "Calling adaptor");
        map.put("adaptor", "redirecting request to service");
        map.put("service", "returning results to adaptor");
        map.put("then adaptor", "returns result to Client");
        map.put("Client and", "adaptor are compatible");
        map.put("Client has", "HashMap ,Service execute() method expects String ,String parameters");
        map.put("so client", "is incompatible to call service directly");
        map.put("adaptor has",
                "execute() method parameters as HashMap , So makes client compatible to call adaptor");
        map.put("further adaptor",
                "transform the input parameter and covert it in format as expected by service");
        map.put("thus", "Client execute service execute() method with the intervention of adaptor");
        map.put("adator class", "Acts as adaptor here to make Client call Service.");



Interface For Adaptor Class that defines the execute method signature
interface IAdaptor {

    void execute(Map map);

Adaptor Class . It takes parameter from client ,transform the input in parameters expected by service class and then execute service class method
class Adaptor implements IAdaptor {
    IService service;

    public void execute(Map map) {
        service = new Service();

        Set set = map.entrySet();
        System.out.println("let us print all key value pairs");

        for (Object object : set) {

           Entry entry=(Entry)object;

            service.execute(entry.getKey().toString(), entry.getValue().toString());



Interface for service class
interface IService {
    public void execute(String key, String value);

Service class .It has the acutal method that execute the required logic and It expects the parameter as String,String
class Service implements IService {

    public void execute(String key, String value) {
        System.out.println(  key + "--->  " + value);




Let Us see the output now
Client--->  Calling adaptor

adaptor--->  redirecting request to service

service--->  returning results to adaptor

then adaptor--->  returns result to Client

Client and--->  adaptor are compatible

Client has--->  HashMap ,Service execute() method expects String ,String parameters

so client--->  is incompatible to call service directly

adaptor has--->  execute() method parameters as HashMap , So makes client compatible to call adaptor

further adaptor--->  transform the input parameter and covert it in format as expected by service

thus--->  Client execute service execute() method with the intervention of adaptor

adator class--->  Acts as adaptor here to make Client call Service.

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