IllegalArgumentException vs. NullPointerException: When Should You Throw Which for Null Parameters?

When to Use IllegalArgumentException vs. NullPointerException for Null Parameters

When setting properties in your code, you may encounter null values that are inappropriate for a particular property. A common dilemma arises: should you throw an IllegalArgumentException (IAE) or a NullPointerException (NPE)?

The Java documentation for both exceptions hints at their appropriateness, but there seems to be some uncertainty. To resolve this question, let's explore the reasons for using IAE exclusively for null parameter validation:

1. JavaDoc Clarity:
The NPE documentation explicitly specifies its use cases as those thrown by the runtime for inappropriate null usage. In contrast, the IAE documentation clearly states that it should be used "for illegal or inappropriate arguments."

2. Stack Trace Implications:
NPEs in stack traces typically suggest that a null was dereferenced. IAE, on the other hand, implies that an illegal value was passed as a parameter. For null parameter validation, the latter interpretation is more accurate.

3. Default Exception for Parameter Validation:
IAE is intended as the default choice for validating parameters. Using NPE would deviate from this convention and suggest a difference in handling from other incorrect parameters.

4. Consistency:
All other types of incorrect parameter data generate IAE. Using NPE for null parameters creates an inconsistency that is not warranted.

5. API Inconsistency:
While some parts of the Java API use NPE for null parameter validation, the API's inconsistency is not a sufficient reason to adopt this approach. It's better to follow established conventions and ensure consistency in your codebase.

Therefore, the recommended approach is to use IAE exclusively for validating null parameters. It provides clear documentation, accurate stack trace interpretation, aligns with convention, and promotes consistency in your codebase.

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