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The content of a package can be scattered across many files.
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Syntax
The following statement at the top of a file makes the code in a file part of the package foo.bar.
package foo.bar
Hierarchy
Package hierarchies should be reflected in directory structure.
A source file defining class myClass in package foo.bar should be stored in a subdirecotory as foo/bar/myClass.scala/
Scala does not really enforce this convention, but some tools such as the Scala IDE for eclipse might have problems otherwise.