Hello,
On 2/6/2013 11:32 PM, Bruce Chapman wrote:
Stephen, In your case(s) would the workaround fail to work if the bug
was fixed?
Working around a bug is quite different to taking advantage of the
buggy behaviour. If fixing the bug would break code that works around
it that can be seen as a problem, while breaking code that relies on
the bug is IMHO much less of an issue since anyone that does that is
taking a known risk, or a risk that should reasonably be expected to
be known.
I am finding it hard to imagine a genuine attempt at a workaround that
would not still work (though redundantly) if the bug was fixed.
Also bear in mind that there are other implementations, and the
signature and the javadoc are the spec. If you find behaviour that
differs and take advantage of that behaviour then you are opening the
possibility of it changing if either: you run with another
implementation, or the bug gets fixed.
While it is easy to contrive an example that would break if this bug
were fixed, and it is possible (on the grounds that I cannot prove it
is impossible) that some real code might break, it is hard to imagine
a scenario where the author/owner of that broken code has any morally
legitimate grounds for complaint in that case.
I guess if you take the "This is one of those unfortunate cases where
a bug can become a feature." approach to its logical conclusion then
no bugs get fixed because there are no bugs, just a nice online list
of newly discovered unexpected features.
As noted earlier in this thread, we use a nuanced compatibility policy
in evolving the JDK:
http://cr.openjdk.java.net/~darcy/OpenJdkDevGuide/OpenJdkDevelopersGuide.v0.777.html
In particular, besides looking after source and binary compatibility, we
also look to manage behavioral compatibility, that is, to be mindful of
changing what a method does at runtime when called, even when the
specification gives us leeway to do so.
Let me relate an example of behavioral compatibility from JDK 7. The
method Class.getMethods returns an array of Method objects for the Class
and in part its javadoc has long stated:
"The elements in the array returned are not sorted and are not in
any particular order."
Therefore, any caller of Class.getMethods relying on or assuming a
particular order has a bug according to the specification. As a
side-effect of permgen removal in JDK 7, the long-standing (and mostly
stable) order of Method objects returned by HotSpot changed. As
expected, some user applications and tests "broke" after this change
went in. We received requests to "fix" the ordering of
Class.getMethods, which we declined to do given the benefits of permgen
removal and the clear specification that no ordering should be relied
upon. Even though that change in getMethods is allowed by
specification, it is out-of-bounds of what we would do an an update
release but in-bounds for a platform release like JDK 7.
The reason for this conservatism is because we value keeping the broad
usage of the JDK working :-)
Getting back to BigDecimal.stripTrailingZeros, we cannot inspect all
usages of this method today, nor can we inspect all the future usages of
BigDecimal.stripTrailingZeros that will be around before JDK 8 is
adopted for the code in question. We know not everyone migrates to a new
JDK release promptly; within the past two years I fielded a
query/complaint about the behavior change in BigDecimal.toString made
between 1.4.2 and JDK 5 and later.
For these sorts of reasons, the default resolution when the
specification and implementation conflict is to make the specification
match the implementation. There are exceptions to this default. Given
sufficient evidence that changing the behavior of
BigDecimal.stripTrailingZeros would not have adverse consequences on
fielded code, we could change its behavior despite being implemented
that way for about 9 years.
-Joe
Bruce
On 7/02/2013 12:16 p.m., Stephen Colebourne wrote:
On 5 February 2013 09:09, Paul Sandoz <paul.san...@oracle.com> wrote:
This is one of those unfortunate cases where a bug can become a
feature.
I *really* don't see how.
The method name is absolutely clear about its purpose. "Strip trailing
zeros". Anyone relying on it not stripping zeroes for zero needs their
head examining.
This particular one just happens to be one that I've run across twice
and in both cases it required a workaround. I'd argue that there are
more people with undiscovered bugs in their code because the method is
buggy than people who would break were the method fixed.
What bothers me even more is the desire expressed in this thread to
simply wish away bugs by redefining the documentation. If the method
name is clear enough, like in this case, then its a bug, and a
documentation change simply isn't the right solution.
Stephen
