Potentially, both of them might be null. Let's see how we can avoid NullPointerException. Can we improve this solution? Yes, we can use Optional. Using map function we can write equivalent similar to the previous statement:. Does optional provide benefits compared to simple null check? Yes, it does. Optional reinsures us that data we use in ifPresent lambda is not null. But, what if the user or address is null? Then, ifPresent will be silently ignored. And, even if we forget to use Optional features, the idea will highlight.
The optional feature was released in Java 1. There are a couple of reasons:. So, for the mentioned reasons some teams prefer to use null checks. And in order to avoid any NPE exceptions, cover such logic with a bunch of tests. Two "solutions" are shown above, are they really solutions? Null check together with Optional serving to the same purpose -- to provide validation for data that might be null. Additionally, Optional reminds the developer that returned value can be null.
But, in general, the key problem is hidden in human nature -- to forget or miss potential null scenarios. We need a solution that will point to the developer what he missed on the compilation step.
We need a solution that can read our code on the compilation step and notify us that we missed a potential NPE scenario. For this purpose, we can use Java Annotation Processors. Java Annotation Processors have many purposes but can be used for our case as well. In this article, you can find an example of how to use an annotation processor in order to check mutability. There are a couple of annotation processors related to NPE problems. Not all of them are the same and follow completely different approaches.
In the next chapter, we review existent NotNull and Nullable annotations providers. Lombok NotNull Annotation is used to generate not null checks that can prevent execution but only in Runtime.
So it doesn't fit our purpose. Shortly, this annotation does the next thing:. Checker Framework provides NonNull and Nullable annotations together with a compiler processor step that can identify potential null checks. The framework can find potential nulls by forcing developers to specify Nullability.
These null objects need to be checked to ensure that they are not null while accessing any member or invoking any methods. This is because members or methods typically cannot be invoked on null objects. The null object design pattern describes the uses of null objects and their behavior in the system.
Instead of checking for the null object, we define null behavior or call do-nothing behavior. These null objects can also be used to provide default behavior in case data is unavailable. The advantage of this approach over a working default implementation is that a null object is very predictable and has no side effects — it does nothing.
The null object pattern can also be used to act as a stub for testing, in case a resource is unavailable for testing. This pattern should be used carefully. It can make bugs appear as a normal program execution. We should not implement this pattern just to avoid null checks and make the code more readable. Actually, it is harder to read code that is moved to another place, like the null object class.
We have to perform additional testing to make sure that there is nowhere we have to assign a null instead of the null object. Create an abstract class or interface to specify various functionalities. I am using the shape interface for this example. Please note that I have created a method isNull as well in the interface.
It's nice to have a method, and I like it because I can better identify and control null-defined objects. This method will return false for all of the concrete classes. And, it will return true only for the null object class. You will need to create a concrete class that extends this class or implements the interface.
Each concrete class will define a specific version of the functionalities. I am defining three types of the shape: Circle , Rectangle , and Triangle.
These concrete classes will define different types of shapes. Below is the code for the Circle class:. Below is the code for the Rectangle class:.
Now, the most important step is to create a null object class that extends the abstract class or interface and define the do nothing behavior. The do nothing behavior is like a default behavior in case data is not available. So in Java, 'arrays' are objects which means they can be assigned to Object type i. Object and therefore in case when null is not explicitly cast compiler chooses valueOf char[] over valueOf Object as the most applicable method.
However, here comes the missing part , had there been another overloaded method that was accepting a interface type param remember interface don't extend Object class so they too cause ambiguity in most specific method selection e.
So the bottom line is avoid passing raw null as arguments to methods rather always cast them to param type of the method being called. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Why cast null to Object? Ask Question.
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