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

• https://projectlombok.org/features/NonNull

GitHub Repository

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

Related Project Lombok Articles

1. Project Lombok - @NonNull Annotation Example

2. Project Lombok - Getter, Setter, and Constructor Example 

3. Project Lombok - toString(), equals() and hashCode() Method Example

4. Project Lombok - @Data Annotation Example
5. Project Lombok - Builder Pattern using @Builder Annotation

6. Project Lombok - Logging @Slf4j Annotation Example
7. Project Lombok - Automatic Resource Management using @Cleanup

8. Project Lombok - @Synchronized Annotation Example 

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