Re: primitive wrapper classes

Eric Sosman <esosman@ieee-dot-org.invalid>
Sat, 22 Sep 2007 08:41:37 -0400
Roedy Green wrote:

On Fri, 21 Sep 2007 14:34:31 -0700, ""
<> wrote, quoted or indirectly quoted someone who
said :

I was just wondering what the main purpose of the primitive wrapper
is in Java.

If you mean the immutable wrappers like Long and Double, for one thing
you can write a method that takes a Number, and pass it a Long,
Double, Integer etc. The method can process the parm differently
depending on its actual type.

     That doesn't seem like a big advantage. If the method
processes the argument differently depending on its actual
type, then it's really just N methods folded into one and
divided up by `instanceof' tests or equivalents. (The dodge
of using doubleValue() on all types indiscriminately runs into
trouble with Longs of large magnitude.)

     Note, too, that Number is non-final: a method that takes
a Number and makes decisions based on `instanceof' cannot hope
to enumerate all subclasses of Number. Indeed, the suite of
native-to-the-JRE classes that implement Number has grown with
succeeding Java versions. (Of course, things like BigDecimal
are not wrappers for primitives, and things like AtomicLong
are not immutable. Still, the problem of writing the method
remains: You might test for a fixed set of "expected" Number
subclasses and throw IllegalArgumentException if given something
else, but ...)

     This isn't to say that methods taking or returning Number
can't be useful; they certainly can be. But methods that choose
different paths by peeping through the Number curtain limit
their own usefulness.

Eric Sosman

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