UML Do you still show composition/aggregate objects as member variables?

If I had a class Airplane and a class Win开发者_运维问答g, if there was a composition relationship between the two, does Airplane have a member variable of type Wing in the class diagram, shown in the Airplane box?

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ASCII art!

+-------------+ 1        1..* +----------+
|  Airplane   |<*>------------|   Wing   |
+-------------+               +----------+

where <*> represents a filled diamond, indicating composition. I used multiplicity 1..*, since it's possible to have aircraft that are essentially a single wing (such as the B-2), and although nobody builds them anymore AFAIK, you have biplanes (2 or 3 wings, depending on how you're counting), triplanes, etc.

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No. Compositions and aggregations are kinds of associations and are shown like associations, i.e., with lines between classes (with solid and hollow diamonds, respectively, on the containing side). As a general rule, if you have an attribute whose type is a class, your model is wrong.

Implementation is a completely separate matter from analysis/design. You may implement associations in a variety of ways, including using member variables e.g. in C++.

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I'm not sure at 100%, but as far I remember no. Is just implicit that u will'have a variable of type Wing.

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No, it doesn't. But that doesn't mean that you can't have an attribute that is of class type. You just can't have both. It's a choice about what you want to emphasise.