Code review: 7012540 (java.util.Objects.nonNull() incorrectly named)
schlosna at gmail.com
Wed Jan 26 16:01:43 UTC 2011
On Tue, Jan 25, 2011 at 6:33 PM, Brian Goetz <brian.goetz at oracle.com> wrote:
>>> Additional notes: After much discussion on core-libs-dev, the name
>>> requireNonNull() seemed the least objectionable.
>> I think requireNonNull(x) is confusing.
> Remember there's two versions of someModifierNonNull being discussed; the
> one currently in Objects is the precondition-enforcing variety, not the
> postcondition-ensuring variety. Are we talking about the same thing?
>> For those familiar with the "requires/ensures/modifies" triad of verbs as
>> a compact way of identifying the preconditions, postconditions, and side
>> effects of a method or procedure in a comment, a specification, or a more
>> formal design-by-contract framework, "requires" is just wrong.
>> When analyzing the invocation of foo in your example, the non-nullity of
>> s and t are preconditions of foo and therefore postconditions of the
>> check method. Naming the check method "requireNonNull" suggests that
>> the check method itself has a precondition that its argument be non-null,
>> when in fact it's the check method's postcondition which ensures that
>> Since postconditions are labeled "ensures" in the "r/e/m" triad, this
>> method should be named "ensureNonNull".
> Right, there's precedent for "ensureXxx" methods to actually change the
> state of things to ensure the postcondition, such as ensureCapacity()
> methods in the collection implementations. Given that a part of the
> motivation for this change was to leave room in the namespace for both the
> precondition-enforcing variety (barf on null) and the postcondition-ensuring
> variety, aka the carpet-sweeping variety ("if it is null, make it non-null")
> ensureNonNull sounds a lot more like the the carpet-sweeping version than
> the version being discussed (barf on null).
> The r/e/m framework seems to support require for the throwing version (as
> implemented by this patch): for the throwing version, non-nullity is a
> precondition of the check method (if the condition is not met, error),
> whereas for the carpet-sweeping version, it is a postcondition of the check
> method (if the check method can come up with a reasonable default value).
> (It happens to be a postcondition of both, but the significant behavior and
> use of the throwing version currently in Objects is to enforce an error when
> the precondition is not met.) Therefore:
> requireNonNull(x) -> throw if x == null
> ensureNonNull(x) -> convert x to a non-null value if null
> seems like the right taxonomy.
If you're still open to other possible names for the requireNonNull
method, based on some of the evaluation comments on the highest rated
RFE  would you prefer assumeNonNull that throws
NullPointerException when the assumption is violated, otherwise
returns the specified object reference? I honestly don't have a strong
opinion between either requireNonNull or assumeNonNull, but I think it
is at least a small step toward a more comprehensive preconditions
API. As I mentioned before, I'd love to see something along the lines
of Guava's Preconditions or Apache commons-lang's Validate APIs as
part of the JDK, but that is probably best left to JDK 8 to better
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