Re: CLI Java Glitch

Nigel Wade <>
Wed, 22 Jun 2011 11:54:02 +0100
On 21/06/11 22:49, Tom Anderson wrote:

On Tue, 21 Jun 2011, Esmond Pitt wrote:

On 21/06/2011 8:09 AM, Martin Gregorie wrote:

The Java language system does case-sensitive comparisons between class
names and the files that contain them when checking that a class name
matches the file name that contains it

Nitpicking, but it doesn't really do that, does it. It opens a .class
file of the name the user specified, loads the class(es) it contains,
and tries to find the classname it was looking for among those
classes. It doesn't explicitly compare the filename and the classname.
The operating system gave it HelloWorld.class in response to
'helloworld.class' because that's how the OS file system happened to

The way Java does this at the moment means that 'java helloworld', where
there is no class 'helloworld', does different things on Windows
depending on whether there is a class HelloWorld, hElLoWoRlD,
HelloworlD, etc.

Does it? What different thing does it do?

As far as a case-insensitive OS/filesystem is concerned, they would all
appear as the same file. If Java asked for any of those names from the
filesystem it would get the one file which did exist for any of the
class names. It would then look in that file for the class it required.
If the class did not exist in that file it would throw the
ClassNotFoundException. It cannot do anything else because the
OS/filesystem simply will not allow it.

Java actually throws ClassNotFoundException in all cases, on all OS,
just as it should. The only difference is that in a case-insensitive
filesystem Java actually opens the case-insensitive filename before it
discovers that it does not contain the class required. On case-sensitive
filesystems the correct case filename won't be found. The actual result
is the same in both cases, a ClassNotFoundException.

That seems pretty shoddy to me. If you're a case-sensitive program
running on a case-insensitive operating system, i think it falls on you
to pay special attention to case in your dealings with that system: when
java opens a class file, it ought to check that the name of the file
it's opened actually has the right case, and if it doesn't, discard it,
and act as if it had got a file not found error from the operating system.


But Java cannot do this. On a case-insensitve OS/filesystem it simply
may not be possible for a file to exist called HelloWorld.class.

Java is not doing anything wrong. The user is, in assuming that because
the OS/filesystem is case-insensitive that Java is also. The java
command syntax is "java <ClassName>" not "java <filename>". That class
name is case sensitive, no matter how brain dead the OS or filesystem.
If you ask Java to run the class helloworld when your class is actually
HelloWorld, you have asked it to do the wrong thing. Java is perfectly
correct in telling you this.

If you ask Java to run the class HelloWorld, it does so even on a
case-insensitive system such as that of the OP. Even if the file is
called helloworld.class Java still manages to do the right thing.

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