Design Patterns: Factory

What is factory pattern

Factory pattern is a creational pattern. It defines an interface for creating different type of object on the run-time. In this factory pattern, it is easy to scale-out when ever you want to add more type.

Example

Here is an example. Car is an abstract class. SmallCar,SedanCar and LuxuryCar extended Car class. CarFactory class has one static method to create different cars accroding to the input paramaters.

• Car, it is a abstract class and has abstract showStage method inside.

  java

  package factorypattern;
  
  public abstract class Car {
      protected CarType model = null;
  
      public Car(CarType model){
          this.model =model;
          System.out.println(model + " is made");
      }
  
      protected abstract void showStage();
  
  }

• CarType, it is a enum type that store different type of cars

  java

  package factorypattern;
  
  public enum CarType {
      SMALL,SEDAN, LUXURY
  }

• LuxuryCar, one type of car that extends Car class

  java

  package factorypattern;
  
  public class LuxuryCar extends Car {
  
      LuxuryCar(){
          super(CarType.LUXURY);
          showStage();
      }
  
      @Override
      protected void showStage() {
          System.out.println("Builing a "+this.model+ " car ..");
      }
  }

• SedanCar, one type of car that extends Car class

  java

  package factorypattern;
  
  public class SedanCar extends Car{
  
      public SedanCar() {
          super(CarType.SEDAN);
          this.showStage();
      }
  
      @Override
      protected void showStage() {
          System.out.println("Builing a "+this.model+ " car ..");
      }
  }

• SmallCar, one type of car that extends Car class

  java

  package factorypattern;
  
  public class SmallCar extends Car {
      public SmallCar() {
          super(CarType.SMALL);
          this.showStage();
      }
  
      @Override
      protected void showStage() {
          System.out.println("Builing a "+this.model+ " car ..");
      }
  }

• CarFactory, it provides a static method to create different type of cars according to the input

  java

  package factorypattern;
  
  public class CarFactory {
      public static Car buildCar(CarType model){
          Car car = null;
          switch (model){
              case SMALL:
                  car = new SmallCar();
                  break;
  
              case SEDAN:
                  car = new SedanCar();
                  break;
  
              case LUXURY:
                  car = new LuxuryCar();
                  break;
  
              default:
                  break;
          }
          return car;
      }
  }

• TestFactoryPattern, there shows how we test factory method. In this main method, different cars will be created through static method of CarFactory.

  java

  package factorypattern;
  
  public class TestFactoryPattern {
      public static void main(String[] args) {
          System.out.println(CarFactory.buildCar(CarType.SMALL));
          System.out.println(CarFactory.buildCar(CarType.SEDAN));
          System.out.println(CarFactory.buildCar(CarType.LUXURY));
      }
  }