In this article, we will see how to use a factory pattern. Factory pattern is a creational type of design pattern, in short, it provides a way to create objects. Another important point to note about this design pattern is that client who uses factory pattern is not aware of the implementation of the factory pattern.

Even in our previous post Spring Boot REST CRUD API, we have used factory pattern to implement managers at the service level. As part of this post, we will show another example of the factory pattern. Factory pattern mainly used in cases when a client just needs a class/object that can handle the job of doing the work at runtime without knowing any details of how it was implemented.

To show how to implement a factory pattern, let’s assume we have different types of vehicles and we want to know what their maximum speed is.

Create an interface –

Our interface of the vehicle will have a method to return the max speed of the vehicle.

package com.betterjavacode.designpatterns.factoryexample;

public interface Vehicle 
{
    void speed();
}

Now, we will have different classes (car, truck,bus,motorcycle) that will implement this interface to return their maximum speed. For article purposes, we will only be showing one class.

package com.betterjavacode.designpatterns.factoryexample;

public class Car implements Vehicle 
{
  public void speed()
  {
     System.out.println("Max Speed of this car is 100 mph");
   }
}

To get an instance of an object, we will create a factory class. This will return an appropriate instance of vehicle object based on vehicle type.

package com.betterjavacode.designpatterns.factoryexample;

public class VehicleFactory 
{

  public Vehicle getVehicle(String vehicleType)
  {
     if (vehicleType == null)
     {
        return null;
     }
     if (vehicleType.equalsIgnoreCase("car")) 
     {
        return new Car();
     }
     if (vehicleType.equalsIgnoreCase("bus")) 
     {
        return new Bus();
     }
     if (vehicleType.equalsIgnoreCase("motorcycle"))
     {
        return new Motorcycle();
     }
     if ( vehicleType.equalsIgnoreCase("truck"))
     {
        return new Truck();
     }
     return null;
}

}

A factory pattern demo class will get any of object of type vehicle at runtime.

package com.betterjavacode.designpatterns;

import com.betterjavacode.designpatterns.factoryexample.Vehicle;
import com.betterjavacode.designpatterns.factoryexample.VehicleFactory;

public class FactoryPatternDemo
{
    public static void getSpeed(String vehicleType) 
    {
       VehicleFactory vehicleFactory = new VehicleFactory();
       Vehicle veh1 = vehicleFactory.getVehicle(vehicleType);
       veh1.speed();
     }  
}

In this example, we have shown how to implement a design pattern type factory pattern. The code for this is available design patterns.

References

1. Factory Pattern Example
2. Factory Pattern