Jdk 1.5: auto-unboxing null

Question

<< This message (by a_silent_lamb) yanked from another thread which had gotten hopelessly off-topic. >>
Auto-unboxing:
According to
http://java.sun.com/features/2003/05/bloch_qa.html
JSR-201 has not yet decided how to auto-unbox null.
Any opinion?
My opinion is to throw NullPointerException as perhaps
it is much more consistent to how Java is currently
doing.I think this is an important question. I tend to agree that it should throw an exception, for two reasons:
(1) As the OP said, it's what experienced Java developers will expect to happen.
(2) As Bloch said, automatically converting null objects to default primitive values would permit subtle runtime errors to creep in.
It seems to me that, if you expect the value to be something that can be auto-unboxed, it's your responsibility to ensure that it never becomes null in the first place. Using null to represent a default value is sloppy programming anyway.
But maybe that's just a conservative reflex on my part. After all, JSR-201 and JSR-14 are all about relieving the developer of the burden of writing the same boilerplate code over and over. What's the use of eliminating type checking and casting, only to force developers to check for nulls before auto-unboxing?
I've also been wondering what the default values would be for the various primitive wrapper classes. For the integral types, the obvious answer is zero, and for Booleans, false. But would null Floats and Doubles convert to 0.0, or NaN? And what about Characters?

Answer 1

Imagine if you switched some of your
code from using an array of primitives to an
ArrayList. If autounboxing null results in a
NullPointerException, you'll have to go through all
your code and insert null checks to avoid exceptions.
With the default value instead, you won't have to
rewrite that code.If you switched your primitive array to an ArrayList without auto-(un)boxing, you'd still have to check for null. Using auto-unboxing to ignore nulls that you'd have to handle anyway is lazy programming.
Your OOP solution in this case is not to ignore nulls, but to extend ArrayList to not allow null entries, something like:public class NulllessArrayList extends Arraylist
  public void add (Object obj)
    if (obj == null)
      throw new NullPointerException();
    else
      super.add(obj);
  //etc for any other methods that add to the list
}Then the list would never contain null, and you wouldn't have to worry about it, you'd only have to check for nulls when adding items, and if you use auto-boxing you wouldn't have to even then.