Which `@NotNull` Annotation Should I Choose for My Java Code?

How to Choose the Right @NotNull Annotation for Your Java Code

To enhance code readability and prevent NullPointerExceptions, many developers seek to leverage tooling such as IDE static analysis and FindBugs. However, the proliferation of equivalent @NotNull/@NonNull annotations can be daunting. This article delves into the available options to help you select the most suitable one.

Equivalent Annotations

The following list provides equivalent @NotNull annotations from various packages:

• javax.validation.constraints.NotNull (runtime validation only)
• edu.umd.cs.findbugs.annotations.NonNull (FindBugs/SpotBugs)
• javax.annotation.Nonnull (JSR-305 inactive)
• org.jetbrains.annotations.NotNull (IntelliJ IDEA)
• lombok.NonNull (Project Lombok)
• androidx.annotation.NonNull (Android annotation package)
• org.eclipse.jdt.annotation.NonNull (Eclipse)

Criteria for Selection

With JSR 305 inactive, the choice of @NotNull annotation involves a pragmatic approach.

Syntax

For stylistic reasons, consider avoiding annotations tied to specific IDEs, frameworks, or toolkits. This eliminates the following options:

• android.support.annotation
• edu.umd.cs.findbugs.annotations
• org.eclipse.jdt.annotation
• org.jetbrains.annotations
• org.checkerframework.checker.nullness.qual
• lombok.NonNull

javax.annotation or javax.validation.constraints?

Comparing javax.validation.constraints and javax.annotation, which require additional dependencies, reveals a slight preference for javax.annotation for its brevity.

Implementation

Similarities: All @NonNull annotations have a trivial implementation, except:

• org.jetbrains.annotations (trivial implementation)
• javax.annotation (longer implementation)
• javax.validation.constraints (implementation with runtime annotation)

Differences: Runtime annotations (javax.annotation, javax.validation.constraints, org.checkerframework.checker.nullness.qual) provide additional runtime checks but have less impact than expected.

Usable Contexts

Annotations differ in their usable contexts:

• Some follow JLS 9.6.4.1 style contexts (android.support.annotation, edu.umd.cs.findbugs.annotations, org.jetbrains.annotation, lombok, javax.validation.constraints).
• Others enable annotation on all JLS contexts (lombok, org.jetbrains.annotations).

Conclusion

Based on the criteria discussed, the pragmatic choice for a @NotNull annotation is javax.annotation.Nonnull. Its brevity, runtime annotation, and compatibility with JLS contexts provide a balanced solution for readability, static analysis, and runtime checks.

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