Upcoming change in semantics to try-with-resources on a null resource

[Joe Darcy]

On 2/16/2011 3:06 PM, Joe Darcy wrote:
> Hello.
>
> After due consideration the JSR 334 expert group has decided the 
> semantics of the try-with-resources statement on a null resource 
> should be changed as follows: the compiler-generated calls to close a 
> resource will only occur if the resource is non-null.
>
> Concretely, the semantics of the desugaring of the finally block are 
> changed from
>
> finally {
>  if (#primaryException != null) {
>    try {
>      #resource.close();
>    } catch(Throwable #suppressedException) {
>      #primaryException.addSuppressed(#suppressedException);
>    }
>  } else {
>    #resource.close();
>  }
> }
>
> to
>
> finally {
>  if (#primaryException != null) {
>    try {
>      if(#resource != null)
>        #resource.close();
>    } catch(Throwable #suppressedException) {
>      #primaryException.addSuppressed(#suppressedException);
>    }
>  } else {
>      if(#resource != null)
>        #resource.close();
>  }
> }
>

FYI, inspired by a comment left on my blog [1], javac will hoist the 
null check of the resource, resulting in the semantically equivalent but 
shorter code

finally {
   if (#resource != null)
     if (#primaryException != null) {
       try {
         // if(#resource != null)
           #resource.close();
       } catch(Throwable #suppressedException) {
         #primaryException.addSuppressed(#suppressedException);
       }
     } else {
       // if(#resource != null)
         #resource.close();
     }
   }
}

-Joe

[1] 
http://blogs.sun.com/darcy/entry/project_coin_null_try_with#comment-1297968215000