Unreachable catch classes

[Maurizio Cimadamore]

On 27/04/11 09:05, Maurizio Cimadamore wrote:
> On 27/04/11 03:42, David Holmes wrote:
>> Hi Joe,
>>
>> 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?

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
>>>
>>>
>