Friday, 17 February 2017

Abstract Factory Design Pattern in Java

Intent
Provide an interface for creating families of related or dependent objects without specifying their concrete classes.

Motivation
Abstract Factory patterns work around a super-factory which creates other factories.  This factory is also called as factory of factories and comes under Creational pattern. The abstract factory pattern provides a way to encapsulate a group of individual factories that have a common theme without specifying their concrete classes.
In normal usage, the client software creates a concrete implementation of the abstract factory and then uses the generic interface of the factory to create the concrete objects that are part of the theme. The client doesn't know which concrete objects it gets from each of these internal factories, since it uses only the generic interfaces of their products.
This pattern separates the details of implementation of a set of objects from their general usage and relies on object composition, as object creation is implemented in methods exposed in the factory interface.


Applicability
Use the Abstract Factory pattern when
Ø  A system should be independent of how its products are created, composed, and represented.
Ø  A system should be configured with one of multiple families of products.
Ø  A family of related product objects is designed to be used together, and you need to enforce this constraint.
Ø  You want to provide a class library of products, and you want to reveal just their interfaces, not their implementations.

Consequences
The Abstract Factory pattern has the following benefits and liabilities:
Ø  It isolates concrete classes. The Abstract Factory pattern helps you control the classes of objects that an application creates.
Ø  It makes exchanging product families easy. The class of a concrete factory appears only once in an application—that is, where it's instantiated.
Ø  It promotes consistency among products. When product objects in a family are designed to work together, it's important that an application use objects from only one family at a time.
Ø  Supporting new kinds of products is difficult. Extending abstract factories to produce new kinds of Products isn't easy.



Implementation
1.      Create a class Car

public abstract class Car {

   public abstract String getHorsePower();
   public abstract String getSeatingCapacity();
   public abstract String getMileage();
  
   @Override
   public String toString() {
   return "Horse Power : " + this.getHorsePower() +
   ", Seating Capacity : "+this.getSeatingCapacity() +  
         ", Mileage : "+this.getMileage();
   }
}

2.      Create sub class Sedan of class Car
public class Sedan extends Car{

   private String horsePower;
   private String seatingCapacity;
   private String mileage;
  
public Sedan(String horsePower, String seatingCapacity, String mileage) {
         this.horsePower = horsePower;
         this.seatingCapacity = seatingCapacity;
         this.mileage = mileage;
   }

   @Override
   public String getHorsePower() {
         return this.horsePower;
   }

   @Override
   public String getSeatingCapacity() {
         return this.seatingCapacity;
   }

   @Override
   public String getMileage() {
         return this.mileage;
   }

}




3.      Create another sub class SUV of class Car
public class SUV extends Car{
   private String horsePower;
   private String seatingCapacity;
   private String mileage;
  
public SUV(String horsePower, String seatingCapacity, String mileage) {
         super();
         this.horsePower = horsePower;
         this.seatingCapacity = seatingCapacity;
         this.mileage = mileage;
   }

   @Override
   public String getHorsePower() {
         return this.horsePower;
   }

   @Override
   public String getSeatingCapacity() {
         return this.seatingCapacity;
   }

   @Override
   public String getMileage() {
         return this.mileage;
   }
}

4.      Create Abstract factory interface  (Notice that the createCar() method returns an instance of super class Car)
public interface CarAbstractFactory {
   public Car createCar();
}

5.      Now we will create Factory class for Each sub class i.e SedanFactory and SUVFactory class
public class SedanFactory implements CarAbstractFactory{

   private String horsePower;
   private String seatingCapacity;
   private String mileage;

   public SedanFactory(String horsePower, String seatingCapacity, String mileage) {
         this.horsePower = horsePower;
         this.seatingCapacity = seatingCapacity;
         this.mileage = mileage;
   }
         @Override
   public Car createCar() {
         return new Sedan(horsePower,seatingCapacity,mileage);
   }
}

public class SUVFactory implements CarAbstractFactory{

      private String horsePower;
      private String seatingCapacity;
      private String mileage;

      public SUVFactory(String horsePower, String seatingCapacity, String mileage) {
            this.horsePower = horsePower;
            this.seatingCapacity = seatingCapacity;
            this.mileage = mileage;
      }
     
      @Override
      public Car createCar() {
            return new SUV(horsePower,seatingCapacity,mileage);
      }
}

6.      Create a class that will provide the entry point for the client classes to create sub-classes.
public class CarFactory {
public static Car getCar(CarAbstractFactory factory){
   return factory.createCar();
}
}

7.      Write a class with the main() to test your code.
public class Main {
public static void main(String[] args) {
Car sedan=CarFactory.getCar(new SedanFactory("2.2", "5", "15 KMPL"));
   System.out.println("Details of Sedan : "+sedan);
  
   Car suv=CarFactory.getCar(new SUVFactory("3.5", "07", "12 KMPL"));
   System.out.println("Details of SUV : "+suv);
}
}


We will get the following output.

Abstract Factory Design Pattern
Abstract Factory Design Pattern 

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