Unfortunately, you can't use packageName.packagerResources.file.data when referring to an external resource or File because the . is not a path separator in any system. The best you can do is packageName/packageResoures/file.data because the forward slash is a recognized path separator. You can also use the ClassLoader.getResource() with that type of path to get a URL to the data (which you may be able to turn into a File) or you could use ClassLoader.getResourceAsStream() to get it directly as an InputStream if what you want to do is read from it. You can even shorten the thing if you are in the packageName.file.class by using getClass().getResourceAsStream("packageResource/file.data").
Show the code that uses that line, check spelling, remember that the path is case sensitive (even if the underlying OS is not (for example in Windows pacakageName is the same as PACKagename, but in Java they aren't the same).