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From: Lew <lewbloch@gmail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: java.io.File
Date: Tue, 6 Dec 2011 09:23:12 -0800 (PST)
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Mayeul wrote:
> Lew wrote:
>> How, then, do calls like 'File#canRead()', 'canWrite()', 'createNewFile()', 
>> 'createTempFile()', 'delete()', 'exists()', 'getFreeSpace()', 
>> 'isDirectory()', 'isFile()', 'list()', 'listFiles()', 'mkdir()', 'mkdirs()', 
>> 'setReadable()', 'setReadOnly()' and 'setWritable()' work?
> 
> I would have said, by merely looking up files or trying to create files 
> of the pathname the instance represents. But maybe my poor English 
> communication skills are getting in the way.

The word "merely" is a dodge.  "Looking up" and "trying to create" involve 
system calls to the OS.  The 'File' object has methods that affect and report 
on the state of the real world, not just the abstract pathname, so obviously in 
order to do that it has to interact with system calls.  Perhaps they aren't 
file descriptors through which the instance asks a directory what files it 
lists, or by which it creates a temporary file, but they sure as heck are 
resources that have to be released.

>> Maybe those operations don't use file descriptors, but they do use OS 
>> filesystem resources.
> 
> Those operations obviously do, but it seemed to me they were loosely 
> tied to the internal state of java.io.File instances.

And therefore ...?

Clearly they are tied to the 'File' instance state, and not "loosely", either.  
That is just as clear as that these operations interact with the file system 
and therefore use OS resources.

It is puzzling to me how anyone can make the argument that an object is 
independent of the file system while acknowledging that it interacts with the 
file system.  Sure, 'File' doesn't have a 'close()' method, but it has 
operations that open things.  One assumes that such operations are RAII, but 
one also recognizes that this is an assumption.

-- 
Lew