java regular expression to match file path

Java is using backslash-escaping too, you know, so you need to escape your backslashes twice, once for the Java string, and once for the regexp.

"([a-zA-Z]:)?(\\\\[a-zA-Z0-9_.-]+)+\\\\?"

Your regexp matched a literal '[-zA-Z0-9_-' string, and a literal '?' at the end. I also added a period in there to allow 'abc.txt'..

That said, consider using another mechanism for determine valid file names, as there are different schemes (i.e. unix). java.util.File will probably throw an exception if the path is invalid, which might be a good alternative, although I don't like using exceptions for control flow...

Use this regex:

"([a-zA-Z]:)?(\\\\[a-zA-Z0-9._-]+)+\\\\?";

I added two modifications: you forgot to add . for matching the file name abc.txt and backslash escaping (\\) was also needed.