Using Composition in Object Modeling

Using composition over inheritance is a common design pattern that is often discussed in terms of designing business logic components. However, composition can solve a number of problems in domain object modeling that are created by relying on inheritance to share interface or functionality. Composition is used to delegate implementation in logical units by enlisting the help of a reference to an object that implements the required functionality instead of inheriting from it. This reference can be changed to different implementations depending on the needs at the time making for a more flexible design. This same design can be used in domain modeling to overcome some of the problems caused by inheritance. The typical flawed example of using inheritance in object modeling is the Person class which is often subclassed into Employee, User , Customer and Vendor classes.
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