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I saw this code in OCPJP SE 8 preparation book written by Boyarsky and Selikoff. I don't understand why the first one throws an exception but the third one doesn't. I tried running it through my compiler but no RuntimeException was thrown. I am really confused. What am I missing?
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Are you saying the first one doesn't throw an exception on your machine? It does on a Mac:

Exception in thread "main" java.lang.IllegalArgumentException: URI has an authority component
at sun.nio.fs.UnixUriUtils.fromUri(UnixUriUtils.java:53)
at sun.nio.fs.UnixFileSystemProvider.getPath(UnixFileSystemProvider.java:98)
at java.nio.file.Paths.get(Paths.java:138)

I'm guessing you are on Windows?

In any case, it is wrong because a URI needs to be an absolute reference so Java can find it.
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Actually, URI "file://pandas/cuddly.org" should properly be referring to a relative file path. Subdirectory panda, filename, "cuddly.org".

For reasons left obscure, the syntax of a URL should conform to the following pattern:


For example:


Jean's example seems to have parsed improperly and it's taking the "//" of the authority component as though it were the "//" which is the translated version of the "\\" of a CIFS UNC name.

If my memory is accurate, this would be the proper encoding for a UNC filepath:


Two slashes for the authority marker, 2 to represent the UNC path \\server\share/directory1/directory2/filename.ext. Note that the URL

file://\\server\share\directory1\directory2\filename.ext is technically legal, but you can burn yourself using it, since in Java you have to double-up on backslashes when coding string literals to avoid getting zapped by the escape mechanism:

file://\\\\server\\share/directory1/directory2/filename.ext and other variations on this theme,

Likewise, for local relative file paths:


And absolute paths:


For systems with a single root, such as Unix, Linux, and MacOS



for multi-rooted filesystems like Windows (there are variants on this syntax, but this is one of the cleanest).
Don't get me started about those stupid light bulbs.
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