Lombok @NonNull Annotation Example

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In this blog post, we’ll explore how you can utilize Lombok @NonNull annotation to make your code more resilient against null-related issues.

What is @NonNull? 

The @NonNull annotation in Lombok is designed to help you automatically generate null checks for your variables. By annotating a variable or a method parameter with @NonNull, Lombok will insert a null check at the beginning of the method or constructor, and if the check fails, a NullPointerException will be thrown.

Without Project Lombok

Without Lombok @NonNull annotation, we need to manually write a code to handle null pointer exceptions:
package net.javaguides.lombok.nonnull;

import net.javaguides.lombok.User;

public class NonNullExample {
    private String name;

    public NonNullExample(User user) {
        if (user == null) {
            throw new NullPointerException("person is marked @NonNull but is null");
        }
        this.name = user.getFirstName();
    }

    public static void main(String[] args) {
        NonNullExample example = new NonNullExample(null);
    }
}

With Project Lombok

With Project Lombok, we are not writing any code to handle null pointer null but we are just adding @NonNull annotation: 
package net.javaguides.lombok.nonnull;

import lombok.NonNull;
import net.javaguides.lombok.User;

public class NonNullLombokExample {
    private String name;

    public NonNullLombokExample(@NonNull User person) {
        this.name = person.getFirstName();
    }

    public static void main(String[] args) {
        NonNullLombokExample example = new NonNullLombokExample(null);
    }
}
The @NonNull annotation automatically generates that null check for you.

Common Use Cases 

Method Parameters: As seen above, you can use @NonNull to annotate method or constructor parameters to ensure that they are never passed a null value. 

Field Initialization: You can use @NonNull on fields that are expected to be initialized immediately, either directly or through a constructor. 

Limitations and Considerations 

While @NonNull is beneficial, there are certain things to keep in mind: 

Lombok doesn't add null-checks everywhere: and Lombok adds null-checks in constructors, setters, and builder methods. It won't add checks to general methods or in other places. 

Runtime Overhead: Remember that the checks Lombok adds are runtime checks. They will slightly increase the execution time whenever they're triggered. However, this overhead is usually negligible.

Debugging: If you're not familiar with Lombok, it might initially be confusing when you see a NullPointerException thrown from a line that doesn't contain an explicit null check. It's essential to remember that Lombok has added these checks during the compilation process.

Reference

GitHub Repository

You can view the source code of this article on my GitHub repository at https://github.com/RameshMF/project-lombok-tutorial

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