Re: Unchecked Cast

From:
Joshua Cranmer <Pidgeot18@verizon.invalid>
Newsgroups:
comp.lang.java.programmer
Date:
Thu, 29 Nov 2007 22:09:29 GMT
Message-ID:
<tMG3j.18133$B21.15977@trndny07>
KDawg44 wrote:

Hi,

I am getting an error when I compile my app that i hoping someone can
shed some light on. I am working with OpenChord and am getting a
Serialized object. I am trying to cast that to a RegistrationInfo
Object in my program. I did this by:

                try {
                        return
(RegistrationInfo)chord.retrieve(retrieveKey);
                } catch (ServiceException e) {
                        throw new RuntimeException(e);
                }


A few points:
1. Include a SSCCE; here, the problem is actually very easy to tell, but
the remedy is impossible.
2. Are you really sure that this is what is going on? Since the advent
of Java 5 and generics, the use cases of explicit casting has gone down
dramatically. OOP discourages such casting as part of its framework.

PresenceServer.java:102: warning: [unchecked] unchecked cast
found : java.util.Set<java.io.Serializable>
required: ClientPackage.RegistrationInfo
                        return
(RegistrationInfo)chord.retrieve(retrieveKey);
                                                               ^
1 warning

 >

What am I doing wrong?


An unchecked cast is, to be brief, a cast that throws away generics
information and, as such, destroys some compile-time checking opportunities.

Here, the output is a Set of Serializable objects, which you are trying
to force into a RegistrationInfo object. Without having any access to
the code you are having problems with, I cannot say how to fix this, but
I can guess (especially given your later runtime exception):

You are using an incorrect API. Go to the documentation for the retrieve
method and find out what the proper calls should be.

--
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth

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