try-with-resources and null resource

[Rémi Forax]

  Le 28/01/2011 10:30, Florian Weimer a écrit :

[...]

> By the way, has anybody else seen this phenomenon in their code base?
>
>    InputStream in = null;
>    try {
>      in = new FileInputStream(path);
>      useFile(in);
>    } finally {
>      if (in != null) {
>        in.close();
>      }
>    }
>
> I'm wondering where this is coming from.

You mean, instead of:

   InputStream in = new FileInputStream(path);
   try {
     useFile(in);
   } finally {
     in.close();
   }


This code is very common. I've spied my students to understand why.
It's because FileInputStream throws an exception so
you put it in the try block, after all try/finally is like try/catch.
Then the IDE warn you that 'in' is not accessible in
the finally block. So you put the declaration on top of the block.

   InputStream in;
   try {
    in = new FileInputStream(path);
    useFile(in);
   } finally {
     in.close();
   }

Here the IDE says that 'in' is not initialized if new FileInputStream
throws an exception. So you initialize 'in' to null.
And the IDE warn you because in.close() will throw a NPE.
So you add a null check.

It's the IDE's fault because it should not suggest to initialize 'in'
with null and developer's fault because he blindly follows what the IDE 
says.

Rémi