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A
very important aspect of OOP is to exploit
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similarities
between classes.
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This
often happens when one class is a specialized
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version
of another class – where most operations are
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identical
or similar, but a few differences do exist.
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For
example, a system administrator of an electronic
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mail
system. They receive messages and manage their
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message
collections in the same way as all other users
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do.
In addition, they have special ability to create new
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accounts
(and remove accounts). The set of all
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administrators
is a subset of the set of all users
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