Relationships provide a pathway for communication between objects.
Sequence and/or collaboration diagrams are examined to determine what links between objects need to exist to accomplish the behavior.
If two objects need to talk there must be a link between them.
Classes relate to each other.
In the first modeling stages (analysis), we are interested primarily in these associations and may choose to name them to clarify the meaning of such an association (the names appear in italics).
The association names will usually be verbs:
Most of the associations will have a direction and navigability.
The above association points from Class1 to Class2.
You can think of the direction as "who can see whom", i.e. Class1 can see - or access - Class2 but not the other way around.
If the association has no arrows, it means either that we don't know about the accessibility yet or that both classes see each other (as if there were arrows on both ends of the association):
The name of the association has no effect on the code - it only documents the diagrams.
The simplest and most common superclass-subclass relation is a "generalize" relation and is denoted as a line with a hollow arrow:
The same relation can be also drawn as an inheritance tree:
The author has over three and a half years of experience on developing web and object oriented application with a development focus on server side and enterprise Java .He is a regular writer for the European publication "Programmez!" and writes on and of for some online publications. He can be reached at sameertyagi@usa.net
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