Causes of null pointer exception

Furthermore, can null pointer exception be caught? Do not catch NullPointerException or any of its ancestors. Programs must not catch java. A NullPointerException exception thrown at runtime indicates the existence of an underlying null pointer dereference that must be fixed in the application code see EXPJ.

Null Pointer Exception in Java Programming. NullPointerException is a runtime exception and it is thrown when the application try to use an object reference which has a null value.

For example , using a method on a null reference. NullPointerException is a RuntimeException. In Java, a special null value can be assigned to an object reference. NullPointerException is thrown when an application attempts to use an object reference that has the null value. These include: Calling an instance method on the object referred by a null reference.

Some of the common reasons for NullPointerException in java programs are;. Invoking a method on an object instance but at runtime the object is null. Accessing variables of an object instance that is null at runtime. Throwing null in the program. Accessing index or modifying value of an index of an array that is null. Is NullPointerException checked or unchecked? NullPointerException doesn't force us to use catch block to handle it.

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. So, whenever you return something you have to explicitly declare can returned result be Nullable or NotNullable Let's take a look at the next example:. If we find the object, then we would display its contents.

Sometimes the user may search using the wrong name or id and we would obtain a null from the database. In that case we would like to inform the user that the object was not found. Situation 2 — Object is initialized, but inner variable is null:. This example builds upon the previous one by trying to dereference a null internal variable.

Let us say we want to our program to print out the number of characters in the category description. The most important classes are Object, which is the root of the class hierarchy, and Class, instances of which represent classes at run time. How do you handle exception in Java? Customized Exception Handling : Java exception handling is managed via five keywords: try, catch, throw, throws, and finally. Briefly, here is how they work. Program statements that you think can raise exceptions are contained within a try block.

If an exception occurs within the try block, it is thrown. How can you achieve runtime polymorphism in Java? We can perform polymorphism in java by method overloading and method overriding. Dynamic run time polymorphism is the polymorphism existed at run-time. Here, Java compiler does not understand which method is called at compilation time. Only JVM decides which method is called at run-time.

How do you return a null in Java? In Java, a null value can be assigned to an object reference of any type to indicate that it points to nothing. The compiler assigns null to any uninitialized static and instance members of reference type. In the absence of a constructor, the getArticles and getName methods will return a null reference. What is a Java package and how is it used?

Packages In Java. Package in Java is a mechanism to encapsulate a group of classes, sub packages and interfaces.