Factory Design Pattern

Factory pattern is one of the most used design patterns in Java. This type of design pattern comes under creational pattern as this pattern provides one of the best ways to create an object.

In Factory pattern, we create object without exposing the creation logic to the client and refer to newly created object using a common interface

Where We Use Factory Design Pattern:

The factory design pattern is used when we have a superclass with multiple sub-classes and based on input, we need to return one of the sub-class. This pattern takes out the responsibility of the instantiation of a class from the client program to the factory class.

Why We Use Factory design Pattern:

Factory Method Pattern allows the sub-classes to choose the type of objects to create. It promotes the loose-coupling by eliminating the need to bind application-specific classes into the code.

Implementation:

Step 1

Create an interface.

Shape.java

public interface Shape {
   void draw();
}

Step 2

Create concrete classes implementing the same interface.

Rectangle.java

public class Rectangle implements Shape {

   @Override
   public void draw() {
      System.out.println("Inside Rectangle::draw() method.");
   }
}

Square.java

public class Square implements Shape {

   @Override
   public void draw() {
      System.out.println("Inside Square::draw() method.");
   }
}

Circle.java

public class Circle implements Shape {

   @Override
   public void draw() {
      System.out.println("Inside Circle::draw() method.");
          } 
   }

Step 3

Create a Factory to generate object of concrete class based on given information.

ShapeFactory.java

public class ShapeFactory {
    
   //use getShape method to get object of type shape 
   public Shape getShape(String shapeType){
      if(shapeType == null){
         return null;
      }        
      if(shapeType.equalsIgnoreCase("CIRCLE")){
         return new Circle();
         
      } else if(shapeType.equalsIgnoreCase("RECTANGLE")){
         return new Rectangle();

         } else if(shapeType.equalsIgnoreCase("SQUARE")){
         return new Square();

}
       return null;
   }
}

Step 4

Use the Factory to get object of concrete class by passing an information such as type.

FactoryPatternDemo.java

public class FactoryPatternDemo {

   public static void main(String[] args) {
      ShapeFactory shapeFactory = new ShapeFactory();

      //get an object of Circle and call its draw method.
      Shape shape1 = shapeFactory.getShape("CIRCLE");

      //call draw method of Circle
      shape1.draw();

      //get an object of Rectangle and call its draw method.
      Shape shape2 = shapeFactory.getShape("RECTANGLE");

      //call draw method of Rectangle
      shape2.draw();

 Shape shape3 = shapeFactory.getShape("SQUARE");

      //call draw method of square
      shape3.draw();

}
}

OUTPUT
Inside Circle::draw() method.
Inside Rectangle::draw() method.
Inside Square::draw() method.