IllegalArgumentException or NullPointerException: Which Exception to Throw for Null Setter Parameters?

Null or Invalid Arguments: IllegalArgumentException vs. NullPointerException

A common dilemma when defining a setter method is determining the appropriate exception to throw when a null parameter is received. Both IllegalArgumentException (IAE) and NullPointerException (NPE) seem applicable based on Java documentation.

IAE vs. NPE: The Difference

NPE is typically thrown by the runtime when null is used inappropriately. In contrast, IAE is expressly designed to indicate that an illegal or inappropriate argument has been passed to a method.

Reasons to Use IAE

For a null parameter in a setter method, IAE is preferable to NPE for several reasons:

• Intended Purpose: IAE is explicitly designed for parameter validation, making it the natural choice in this scenario.
• Clarity: An NPE in a stack trace suggests a null dereference, while an IAE indicates an illegal parameter, which is the true cause in this case.
• Consistency: All other invalid parameter data types typically throw IAE, ensuring consistent handling.
• Flexibility: The custom exception message can communicate specific details about the error, eliminating the need for separate NPE handling.

API Usage and Counterargument

While some parts of the Java API use NPE for null arguments, this inconsistent approach should not justify using NPE over IAE in this specific context. The reasons outlined above strongly support the use of IAE for illegal null parameters in setter methods.

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