"When Java packages
are stored in the file system, the host system may
choose to enforce the restriction that it is a
compile-time error if a type is not found in a file
under a name composed of the type name plus an
extension (such as .java
or .jav) if either of the
following is true:
- The type
is referred to by code in other compilation
units of the package in which the type is
declared, or:
- The type
is declared public (and therefore is
potentially accessible from code in other
packages).
This
restriction implies that there must be at most one
such type per compilation unit. This restriction
makes it easy for a Java compiler and Java Virtual
Machine to find a named class within a package. For
example, the code for a public type wet.sprocket.Toad would be found in a
file Toad.java in the directory wet/sprocket. The corresponding
object code would be found in the file Toad.class in
the same directory.
When Java
packages are stored in a database, the host system
need not enforce such restrictions.
In practice,
many Java programmers choose to put each class or
interface type in its own compilation unit, whether
or not it is public, or is referred to by
code in other compilation units."
