Difference between Aggregation and Composition (with Comparison Chart) - Tech Differences
In both aggregation and composition object of one class "owns" object of another class. Both denotes relationship between object and only differ in their strength . . have been defined as special cases of association in UML Class Diagrams. Aggregation in the UML class diagram is represented by an open But why does the UML call out the difference between aggregation and composition? By contrast, composition refers to a stronger relationship where the. Quick answer to a UML FAQ: Association vs Aggregation vs Composition? Consider the differences and similarities between the classes of the Visual Paradigm Community Edition is a UML software that supports all UML diagram types. in addition to the part-of relationship between Class A and Class B - there's a.
But why does the UML call out the difference between aggregation and composition?
UML Association vs Aggregation vs Composition
It doesn't require any difference in coding syntax, at least not in managed code we'll discuss unmanaged code in a moment. It turns out that this distinction is not nearly as important today with managed languages as it was fifteen years ago when we didn't have automatic garbage collection in languages.
In other words, if an object allocates memory for an object then it has the responsibility for de-allocating the memory when it's done using it.
- Difference between Aggregation and Composition
This is not necessarily true for aggregate objects. However, in managed memory languages like Java and C Sharp, this is no longer an important distinction because memory is cleaned up by the garbage collector.
But there is a conceptual difference between aggregation and composition. I like to illustrate it by talking about parking lots. A parking lot has both aggregation and composition in it.
A parking lot is an area that aggregates cars. A parking lot is still a parking lot when there are no cars on it. Aggregation is just a place for the aggregates to inhabit. By contrast, composition refers to a stronger relationship where the composed object is a required part of its composer.
Aggregation or Composition?
For example, a car is composed of an engine, a steering wheel, four tires, etc. By our definition, a car ceases to be a car if you remove the engine.
Composition refers to a strong relationship between the composer and the composed. I like to think of aggregation as referring to the "has-a" relationship and I like to think of composition as referring to the "has-to-has-a" relationship.
Just remember that others may not share that definition and that you might need to explain your use of aggregation to them. The definition I'm using? The 'has a collection of' definition? Association and composition are fairly straightforward. Aggregation is the wobbly one.
Design Codes: UML Class Diagram: Association, Aggregation and Composition
In practice, I find that the 'part of' test is works well 'ownership' is a sub-optimal way to think about it. A person can be part of a club, thus a club aggregates people it does not own them. When the club is destroyed the people continue to exist. Composition relationship We have a class A which will be used by class B. Class B simply cannot exists without A.
This is a huge violation of dependency injection principlewhich says: A dependency is an object that can be used a service.
An injection is the passing of a dependency to a dependent object a client that would use it. The service is made part of the client's state.
Passing the service to the client, rather than allowing a client to build or find the service, is the fundamental requirement of the pattern.