Unreachable catch classes

[Maurizio Cimadamore]

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)'.

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
>>
>>