Weird "Package could not be found" problem

Essentially I've got a problem where in OS X packages are not recognised in Java, ever. I've tried on numerous occasions to use packages 开发者_JAVA技巧and they never work. I know I'm doing it right because the same packages work absolutely fine on Windows. Does anyone know what my problem could be?

Thanks in advance!

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Are you using lowercase names for both the package name and the folder name corresponding to it?