[vfs] Why doesn't AbstractFileObject override equals?

[Stephan Schuster <st...@wilken.de>]

hi together,

on the first glimpse i don't understand why AbstractFileObject doesn't 
override equals() and hashCode(). depending on the concrete 
implementation this may result in Object's identity comparison when 
comparing two file objects which is in most cases definitely not desired 
(see further below). in my opinion a simple solution would be:


     @Override
     public boolean equals(final Object other) {
         if (this == other)
             return true;
         if (other == null)
             return false;
         if (!(other instanceof FileObject))
             return false;

         try {
             return getURL().equals(((FileObject) other).getURL());
         } catch (FileSystemException e) {
             return false;
         }
     }

     @Override
     public int hashCode() {
         try {
             return getURL().hashCode();
         } catch (FileSystemException e) {
             return super.hashCode();
         }
     }


another issue i stumbled upon today: in AbstractFileObject.getParent() 
there's an if-clause like:

     if (this == fs.getRoot()) { ... }

i'm pretty sure that an identity comparison makes no sense here and this 
should rather be changed to

     if (this.equals(fs.getRoot())) { ... }

however, this will only work if equals() is overridden.


what do you think?


regards,
stephan


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Re: [vfs] Why doesn't AbstractFileObject override equals?

[Mario Ivankovits <ma...@ops.co.at>]

Hi!

I'd go that way:
> 1. in AbstractFileObject.getParent():
>
> replace
>
>   if (this == fs.getRoot()) { ... };
>
> with
>
>   FileObject root = fs.getRoot();
>   if (root instanceof DecoratedFileObject) {
>     root = ((DecoratedFileObject) root).getDecoratedFileObject();
>   }
>   if (this == root) { ... }
But instead of the instanceof thing simply use
FileObject root = FileObjectUtils.getAbstractFileObject(root);

Which does all the unpacking stuff.

Ciao,
Mario


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Re: [vfs] Why doesn't AbstractFileObject override equals?

[Stephan Schuster <st...@wilken.de>]

hi mario,

thank you for your answer.

> The current VFS implementation (if you do not use anything else then the 
> only-working SoftRefFilesCache) ensures that two resolveFile will return 
> the same object if you ask for the same filename, thus, in terms of VFS 
> there is nothing bad with the object comparison.

that is what i was hoping as i saw the code for the first time. however 
i always got NPEs somewhere further up in stack. to me it seemed that 
the original cause was always the AbstractFileObject.getParent() method 
or more precisely the comparison

   if (this == fs.getRoot()) { ... };

which never evaluated to true, even if it should! so i tracked down the 
problem a bit further. the reason is the following: under certain 
circumstances my custom filesystemmanager uses CacheStrategy.ON_CALL. on 
resolving a file via this filesystem i therefore get an instance of a 
DecoratedFileObject, in fact an instance of OnCallRefreshFileObject. now 
when calling getParent() on a DecoratedFileObject the call is forwarded 
to the actual implementation of the file object, lets say 
LocalFileObject. then, in the above comparison the "this" pointer is an 
instance of LocalFileObject. however, "fs.getRoot()" which internally 
calls "resolveFile(rootName)" uses the same filesystem and therefore 
returns an instance of OnCallRefreshFileObject. comparing both, 
LocalFileObject and OnCallRefreshFileObject, via identity will never 
work. that's the problem!


there a several solutions:

1. in AbstractFileObject.getParent():

replace

   if (this == fs.getRoot()) { ... };

with

   FileObject root = fs.getRoot();
   if (root instanceof DecoratedFileObject) {
     root = ((DecoratedFileObject) root).getDecoratedFileObject();
   }
   if (this == root) { ... }


2. use equals for the above comparison and overwrite equals in 
AbstractFileObject in such way that the identity comparison respects 
decorated file objects.


3. use the file object's path for determinig equality (as in my last 
posting)



what do think is the best way?


regards,
stephan



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Re: [vfs] Why doesn't AbstractFileObject override equals?

[Mario Ivankovits <ma...@ops.co.at>]

Hi!
> on the first glimpse i don't understand why AbstractFileObject doesn't 
> override equals() and hashCode().
The current VFS implementation (if you do not use anything else then the 
only-working SoftRefFilesCache) ensures that two resolveFile will return 
the same object if you ask for the same filename, thus, in terms of VFS 
there is nothing bad with the object comparison.
Did you catch any problem?

Ciao,
Mario


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