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

Exceptions for Null Parameters: IllegalArgumentException vs. NullPointerException

When designing a Java application, it's crucial to decide whether to throw an IllegalArgumentException (IAE) or a NullPointerException (NPE) when encountering a null parameter. Understanding the intended purpose of each exception is essential for making an informed choice.

Use IllegalArgumentException When:

• A parameter is explicitly defined as non-null and a null value is passed.
• The specific exception you need to throw is for invalid or inappropriate arguments.
• You want to communicate to the caller that they passed an illegal value, not that a null was dereferenced.

Reasons to Avoid NullPointerException for Null Parameters:

• The NPE should only be thrown when null is used inappropriately at runtime.
• Throwing NPE can be misleading, as it suggests a null dereference rather than an invalid parameter.
• IAE is specifically designed for handling illegal parameters and is the default choice.
• Consistency with the handling of other invalid parameters should be maintained.

Example:

public void setProperty(String value) throws IllegalArgumentException {
  if (value == null) {
    throw new IllegalArgumentException("Property value cannot be null");
  }
}

In this example, IllegalArgumentException is a more appropriate choice because it indicates that the application logic explicitly requires a non-null value for the property.

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