The interdependency between methods and object classes is known as coupling.
The binding of the elements within one method and one object class, is known as cohesion.
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Aggregation differs from ordinary composition in that it does not imply ownership. In composition, when the owning object is destroyed, so are the contained objects. In aggregation, this is not necessarily true. For example, a university owns various departments (e.g., chemistry), and each department has a number of professors. If the university closes, the departments will no longer exist, but the professors in those departments will continue to exist. Therefore, a University can be seen as a composition of departments, whereas departments have an aggregation of professors. In addition, a Professor could work in more than one department, but a department could not be part of more than one university.
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Ability of a new class to be created, from an existing class by extending it, is called inheritance
Let's use the following application as an example. Both Graduate class and Undergraduate class have similar bahavior such as managing a name, an address, a major, and a GPA. Rather than put this bahavior in both of these classes, the bahavior is placed in a new class called Student. Both Graduate and Undergraduate become subclass of the Student class, and both inherit the Student behavior.
Both Graduate and Undergraduate classes can then add additional behavior that is unique to them. For example, Graduate can be either Master's program or phD program. On the other hand, Undergraduate class might want to keep track of either the student is Freshman, Sophmore, Junior or Senior.
second again becomes tricky for me but lets try:
Aggregation is a weaker form of relationship compared and it represents a "has-a" relationship and it cannot exist on its own.
Coupling means how the entities will continue to have their independent existence.
Cohesion means a measure in terms of how a classes behaviors and attributes are related.