Hi,
I just wrote my first project in java with eclipse. I installed eclipse saying it that the working space is a certain folder (%userprofile$\eclipse\workspace, with sources into the src subfolder and the compiled files into the bin folder).
I made the first Project (MyProject, eclipse made this folder for me), and wrote some sources with a certain pakages (myProject.calc and java.util.myUtil).
Eclipse don't want that thoose files remain in the right folders, but twice them (instead %userprofile$\eclipse\workspace\src\myProject\calc\SourceFile.class, it wants that they are to be saved in %userprofile$\eclipse\workspace\src\myProject\calc\myProject\calc\SourceFile.class)
If the twicing is not present, the compiler returns an exception (the declared package does not match the expected package). If the twicing is present, the compilation performs a problem (The project cannot be built until build path errors are resolved)