Design Pattern: NullObject

Null Object Pattern is one of good pattern used to avoid NullPointerException.

Null Object is not ‘null’ i.e. it is not default value used for object references.

Problem:

We use the null condtion to check the value is null or not null to avoid Null Pointer Exception But it is not a proper solution because we need to add this check whereever we call a method on our object.

I.e. we need to null check for each object before making the calls finally, unnecessary code and unnecessary checks will be added in our program.

Solution:

Create an object that will do nothing whenever nothing is available for reference.

Let’s see the implementation:

Animal:

public interface Animal {

    public void makeSound();

}

Dog: Actual Animal

public class Dog implements Animal {

    public void makeSound() {

            System.out.println("woof!");

    }

}

NullAnimal: Default Animal

public class NullAnimal implements Animal {

    public void makeSound() {

    }

}

When we know actual animal then we will create that animal class if not applicable we will create NullAnimal with default and it will not do anything.