We have first created a variable of type IMobile and initialized it with an instance of NullMobile. In our main logic, when we try to call methods on this object we will not get any exception and hence the work flow will not break.
However, the methods will do nothing. The null object pattern helps us to write a clean code avoiding null checks where ever possible. Using the null object pattern, the callers do not have to care whether they have a null object or a real object. It is not possible to implement null object pattern in every scenario. Sometimes, it is likely to return a null reference and perform some null checks. In above code sample, we are using an null object implementing an interface.
However, we can have a quite similar approach with Abstract base class also. Null object is often a singleton. However, sometimes we want our object state to vary over instances. Null pattern is helpful in situations where we want to return an object of the expected type, yet do nothing. Though it is not possible to have this pattern incorporated at all the places instead of null references.
But if we want to abstract out the handling of null reference out of client code and when two objects are collaborating with each other as in case of Strategy pattern, this is a must have pattern. And definitely developers working in the client side need to be aware of the presence of null object. Otherwise they will still be doing the null reference checks in the client side. Really nice and easy to understand article, but — as you said in the conclusion — is not possible to use this pattern in all places of a large application.
Yeah this is a very important pattern and can be highly useful for classes which have both state and behaviour. And it is of not much use for the class which only contains state data. This site uses Akismet to reduce spam. Learn how your comment data is processed. Skip to main content Skip to primary sidebar Skip to footer There is a pattern present to handle the null object in programming. Use the CustomerFactory to get either RealCustomer or NullCustomer objects based on the name of customer passed to it.
Arnab Chakraborty. Manoj Kumar. Zach Miller. Isn't it? If your object being null is going to be a norm throughout your code, you'd might as well use the pattern. I check for null when an object has not been created and it needs to be instantiated. I do not really use null for anything else, and I certainly don't use it to mean no behavior defined. If however, you are using null to mean the behavior hasn't been defined yet or the default behavior is nothing, then certainly use the pattern.
From my experience I don't feel it is hard to keep a Null-Object in sync. If you do have this problem, your object may have too many responsibilities as it is subject to a lot of change.
I tend to use this pattern if I can actually define such an object in terms of letting a default behaviour flow well. A Null Object for a Query Manipulation is one that leaves the original query untouched. A Null Extension to some other object is one that does nothing. I find it at times a pretty clean pattern to avoid checking with ifs for optional behaviour that may or may not exist at a certain state of my app.
I've had great success using null objects with my Factories and IoC implementations. They are especially useful for vertical features of an application. I wouldn't create one for an action that is core to your application.
In this case, printing is a feature of the app but not a requirement for it to run successfully.
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