On 27/04/11 09:18, David Holmes wrote:
Maurizio Cimadamore said the following on 04/27/11 18:05:
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)'.
Special-casing Throwable wouldn't be sufficient as people may use
Exception instead.
What I suggested on coin-dev ( which has finally turned up now that
someone has unblocked the openjdk mail pipes ;-) ) is that instead of
doing an analysis of the expected thrown types, to simply warn for the
more common mistake of catching a superclass before a subclass.
So, you are saying that the JDK 7 compiler should stop generating
additional warnings, and start behaving as usual (we always had errors
when catching supertype after subtype, and such).
Maurizio
David
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
