Null Object Pattern

Definition

Null Object Pattern is a behavioral design pattern that is used to create an object represent null, void or not applicable values. For instance, In case a null value is returned by a condition and called a method on it, Null Point Exception will be thrown by the application. To avoid that, We use Null Object Pattern.


Intention

Avoid null point exception trowing by the application





Code

//Null Object 
 public class NoVehicle implements Vehicle {

    @Override
    public String getName() {
      
        return "No vehicle found.";
    }
  
  
}

//Concrete Product

public class Car implements Vehicle {

    @Override
    public String getName() {

        return "This is a car";
    }
}

//Abstraction
public interface Vehicle {

    String getName();

}

// Factory

public class VehicleFactory {

    public static Vehicle getVehicle(String type) {

        if ("Car".equalsIgnoreCase(type)) {
            return new Car();
        } else {
            return new NoVehicle();
        }

    }

}

//Client

public class Client {

    public static void main(String[] args) {

        Vehicle vehicle = VehicleFactory.getVehicle("car");
        System.out.println(vehicle.getName()); // Output: This is a car
      
        Vehicle vehicle2 = VehicleFactory.getVehicle("bus");
        System.out.println(vehicle2.getName()); // Output: No vehicle found.

    }

}