Among the wonderful changes in Java 5 that make code easier to read and maintain (cough) is autoboxing. Consider the following line of code:

return handleIncorrectType(message, modelColumn, o, keyboard);

It was throwing a NullPointerException (not passing one from the underlying method invocation). I had to scratch my head for quite a few minutes to see how it would, as there was no invocation on the parameters that could cause it.

The answer was that one of the parameters was a primitive wrapper type (Boolean) set to a null value, and the autoboxing mechanism punts when coalescing wrapper nulls to primitive types. Fun!

2 thoughts on “Autoboxing Makes Null Fun!

  1. Perhaps throw something like a WrapperNullException with a message like “A primitive wrapper type contained a null value and could not be coerced to a primitive.”

    Nah, that would be too clear. Better to throw an NPE with no specific explanation.

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