CloneNotSupportedException should extends RuntimeException not Exception

Remi Forax forax at
Fri Nov 2 23:05:32 UTC 2012

On 11/02/2012 11:44 PM, Joe Darcy wrote:
> On 10/15/2012 03:56 AM, Alan Bateman wrote:
>> On 15/10/2012 11:28, Joel Borggrén-Franck wrote:
>>> On 10/15/2012 12:34 AM, David Holmes wrote:
>>> > Remi,
>>> >
>>> > This ship has sailed you can't recall it. 
>>> CloneNotSupportedException > is a checked exception and needs to 
>>> remain so for source and binary
>>> > compatibility.
>>> >
>>> I see how this is source incompatible and also behaviorally 
>>> incompatible in a few cases, but how is this binary incompatible? 
>> I think you're right as there wouldn't be a linkage error.
>> his thread reminds of Joe Darcy's classic blog on compatibility kinds:
> Hello,
> Catching up on email, changing the supertype of an exception from 
> Exception to RuntimeException exception is *binary* compatible under 
> the rules for superclasses and interfaces evolution given in the JLS:
> "Changing the direct superclass or the set of direct superinterfaces 
> of a class type will not break compatibility with pre-existing 
> binaries, provided that the total set of superclasses or 
> superinterfaces, respectively, of the class type loses no members."
> Since the subtype (RuntimeException) has all the members of its parent 
> (Exception), and also the same set of constructor signatures, this 
> change is binary compatible and will *not* cause a linkage error at 
> runtime (which is the definition of binary compatible).
> As Brian pointed out, there is a small risk of source and behavioural 
> compatibility change is a try block had both catch clauses for 
> CloneNotSupportedException and RuntimeException.  That in and of 
> itself doesn't rule out such a change since our general evolution 
> policy for the JDK is:
>>     1. Don't break binary compatibility (as defined in the Java 
>> Language Specification).
>>     2. Avoid introducing source incompatibilities.
>>     3. Manage behavioral compatibility changes.
> In some lesser-used corners of the platform, we've made just this sort 
> of change with exception superclasses, in full awareness of the 
> potential issues:
>     6519115 MirroredTypeException thrown but should be 
> MirroredTypesException
> However, given the prevalence of CloneNotSupportedException, I don't 
> think making it an unchecked exception after it was a checked 
> exception is appropriate.

We also add a common super types (ReflectiveOperationException) of all 
exceptions thrown by reflection code.
But in that case, because the exception ReflectiveOperationException 
didn't exist before, there was no problem of compatibility.

BTW, I've found a way to solve the problem of 
CloneNotSupportedException, I don't say that we should do that,
The idea just to explicitly change the JLS to say that 
CloneNotSupportedException is now unchecked.
In that case, this is a binary compatible change and there is no 
behavioural incompatibility.

> -Joe


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