Unreachable catch classes

[David Holmes]

Maurizio Cimadamore said the following on 04/27/11 18:10:
> On 27/04/11 09:05, Maurizio Cimadamore wrote:
>> On 27/04/11 03:42, David Holmes wrote:
>>>
>>> I sent email to coin-dev on this yesterday but it doesn't seem to 
>>> have turned up - at least I haven't seen it.
>>>
>>> In some cases at least these catch clauses are in fact reachable - 
>>> e.g. ThreadPoolExecutor. The analysis assumes that checked-exceptions 
>>> can only be thrown by methods that declare them, but we all know that 
>>> is not the case: Class.newInstance and native methods can throw them 
>>> too (are there other cases?). So sometimes we want the "unreachable" 
>>> catch as a "safety-net" for these cases.
>>>
>>> Given checked-exception checks can be circumvented it seems to me 
>>> that the analysis should not be issuing warnings for these cases 
>>> because it will encourage people to "fix the code" - as you have just 
>>> asked to be done! - when in fact the code could be less robust if it 
>>> is changed.
>> I see your concerns - unfortunately there is no way to statically 
>> distinguish 'good' cases from 'bad' cases - i.e. a call to 
>> Class.newInstance could be hidden behind a method called inside the 
>> try-block. So, it seems like the only sensible option would be to 
>> special case 'catch(Throwable)'.
> 
> Btw - it seems like both Constructor and Method throws 
> InvocationTargetException in order to wrap checked exceptions from user 
> code. Why Class.newInstance does not use ITE ? That'd be for 
> compatibility, right?

Right - Class.newInstance predates the full reflection API and the 
powers that be at the time refused to change it for "compatibility 
concerns" even though it violated the language semantics. :(  It took 
some effort to even get the problem clearly documented in the method.

Because of that and the problem of native code, any framework code 
wanting to ensure that it dealt with all exceptions, has been forced to 
use the kind of pattern we are discussing - and similar ones for 
rethrowing exceptions (by wrapping any unexpected checked-exception in 
an Error).

For some reason "they" never even considered deprecating 
Class.newInstance so that people would at least be steered to use the 
reflection APIs. Though given deprecated APIs never actually disappear 
it makes little practical difference.

David

> Maurizio
>>
>> Maurizio
>>>
>>> Cheers,
>>> David
>>>
>>> Joe Darcy said the following on 04/27/11 11:53:
>>>> Hello.
>>>>
>>>> FYI, javac in JDK 7 does a more precise analysis than before on what 
>>>> catch blocks can actually be reached and warnings are issued for 
>>>> unreachable catch blocks.  I've extracted those warnings from a 
>>>> recent full JDK build in case anyone wants to update the code in 
>>>> question.
>>>>
>>>> -Joe
>>>>
>>>> ../../../../../../src/share/classes/com/sun/corba/se/impl/protocol/BootstrapServerRequestDispatcher.java:124: 
>>>> warning: unreachable catch clause
>>>>        } catch (java.lang.Exception ex) {
>>>>          ^
>>>>  thrown type RuntimeException has already been caught
>>>>
>>>> ../../../../../../src/share/classes/com/sun/corba/se/impl/protocol/BootstrapServerRequestDispatcher.java:124: 
>>>> warning: unreachable catch clause
>>>>        } catch (java.lang.Exception ex) {
>>>>          ^
>>>>  thrown type RuntimeException has already been caught
>>>>
>>>> ../../../src/share/classes/java/util/concurrent/ThreadPoolExecutor.java:1115: 
>>>> warning: unreachable catch clause
>>>>                    } catch (Throwable x) {
>>>>                      ^
>>>>  thrown types RuntimeException,Error have already been caught
>>>> ../../../src/share/classes/java/net/DatagramSocket.java:183: 
>>>> warning: unreachable catch clause
>>>>        } catch(IOException e) {
>>>>          ^
>>>>  thrown type SocketException has already been caught
>>>> Note: Some input files use or override a deprecated API.
>>>> Note: Recompile with -Xlint:deprecation for details.
>>>> Note: Some input files use unchecked or unsafe operations.
>>>> Note: Recompile with -Xlint:unchecked for details.
>>>> 2 warnings
>>>>
>>>> ../../../src/share/classes/java/security/cert/X509CertSelector.java:2217: 
>>>> warning: unreachable catch clause
>>>>        } catch (CertificateException e3) {
>>>>          ^
>>>>  thrown types 
>>>> CertificateNotYetValidException,CertificateExpiredException have 
>>>> already been caught
>>>>
>>>> ../../../src/share/classes/javax/management/modelmbean/RequiredModelMBean.java:1220: 
>>>> warning: unreachable catch clause
>>>>        } catch (Exception e) {
>>>>          ^
>>>>  thrown types 
>>>> InvocationTargetException,IllegalAccessException,RuntimeException 
>>>> have already been caught
>>>> 1 warning
>>>>
>>>> ../../../../src/share/classes/sun/security/rsa/RSASignature.java:205: 
>>>> warning: unreachable catch clause
>>>>        } catch (GeneralSecurityException e) {
>>>>          ^
>>>>  thrown type BadPaddingException has already been caught
>>>>
>>>>
>>
>