RFR: cleanup - removed unneeded casts in jdi

[David Holmes]

Hi Serguei,

On 23/12/2017 6:04 PM, serguei.spitsyn at oracle.com wrote:
> Hi Egor and David,
> 
> 
> Egor,
> 
> The fix looks good in general.
> I've filed bug:
> https://bugs.openjdk.java.net/browse/JDK-8194143
>      remove unneeded casts in LocationImpl and MirrorImpl classes
> 
> 
> On 12/22/17 13:06, David Holmes wrote:
>> Hi Egor,
>>
>> On 23/12/2017 1:32 AM, Egor Ushakov wrote:
>>> Hi all,
>>>
>>> could you please review and sponsor this small cleanup removing 
>>> unneeded casts in jdi LocationImpl and MirrorImpl.
>>> They were preventing creating custom Location and Mirror 
>>> implementations used for tests and IDEA debugger impl.
>>> http://cr.openjdk.java.net/~avu/egor.ushakov/cast_fix/
>>
>> src/jdk.jdi/share/classes/com/sun/tools/jdi/LocationImpl.java
>>
>> !     public int compareTo(Location object) {
>> -        LocationImpl other = (LocationImpl)object;
>>
>> The existing code is somewhat suspect as the Location interface 
>> implements Comparable but it does not specify what it means to compare 
>> two Locations! That's a bug in itself.
> 
> Not sure, if it is really needed as it is abstract.
> We could say: An implementation of the Location is expected to specify it.

That makes it impossible to compare different implementations of the 
Location interface. The functionality has to be specified by the interface.

>> LocationImpl has decided how to compare two LocaltionImp's (but 
>> doesn't even check they are in the same VirtualMachine!).
> 
> Nice catch!
> Interesting...
> Should comparing of locations from different mirrors be a no-op?
> Not sure if it would be right to throw a VMMismatchException in such cases.

Not sure - without knowing why we need to compare Locations it's hard to 
say.

>> Can we generalize that to accommodate other Location 
>> implementations?Your change allows for this to happen, but it will 
>> only work as expected if the other Location implementations use the 
>> same comparison basis as LocationImpl - which is unspecified.
> 
> It is not clear, what you mean here.
> What are the other Location implementations?

The ones that Egor is implementing and the reason for this bug report.

> A JDI implementation normally has one base implementation of the Location.
> What would be a need to have multiple?

Egor indicated it was for use in testing and the IDEA debugger. It's 
apparent they have their own implementation of Location, but these 
instances have to interact with the default LocationImpl implementations 
- else this bug report would not be needed.

Cheers,
David

> And different JDI implementations are not supposed to interact with each 
> other, are they?
> 
> 
>> src/jdk.jdi/share/classes/com/sun/tools/jdi/MirrorImpl.java
>>
>> Change looks good. It would also seem that now this change is made 
>> that this:
>>
>>   37     protected VirtualMachineImpl vm;
>>   38
>>   39     MirrorImpl(VirtualMachine aVm) {
>>   40         super();
>>   41
>>   42         // Yes, its a bit of a hack. But by doing it this
>>   43         // way, this is the only place we have to change
>>   44         // typing to substitute a new impl.
>>   45         vm = (VirtualMachineImpl)aVm;
>>
>> might reduce to:
>>
>>   37     protected VirtualMachine vm;
>>   38
>>   39     MirrorImpl(VirtualMachine aVm) {
>>   40         super();
>>   41         vm = aVm;
>>
>> if we no longer depend on it being VirtualMachineImpl ... and neither 
>> do subclasses.
> 
> Good suggestion.
> 
> 
> Thanks,
> Serguei
> 
>>
>> David
>> -----
>>
>>> I do not have rights to create JDK bug report directly, please create 
>>> it if it is needed for the procedure.
>>>
>>> Thanks!
>>>
>