CSC/ECE 517 Fall 2011/ch17 5b uo: Difference between revisions
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== Representing "Is-a" Relationship == | == Representing "Is-a" Relationship == | ||
A "Is-a" relationship can be represented by inheritance in most cases. | |||
== Code Reuse == | == Code Reuse == | ||
Revision as of 19:30, 30 October 2011
When to use Inheritance
Introduction
Inheritance is a useful programming concept, but it is easy to abuse this concept. Often interfaces or delegation are better options. In this wiki chapter, we will discuss the situations when to use and when not to use inheritance.
Inheritance is a good choice when:
Your inheritance hierarchy represents an "is-a" relationship and not a "has-a" relationship.
You can reuse code from the base classes.
You want to implement polymorphism.
The class hierarchy is reasonably shallow, and other developers are not likely to add many more levels.
You want to make global changes to derived classes by changing a base class.
These points are discussed in detail below
Representing "Is-a" Relationship
A "Is-a" relationship can be represented by inheritance in most cases.
Code Reuse
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Inheritance-based Polymorphism
Shallow Class Hierarchies
Global Changes to Derived Classes Through the Base Class
Composition vs Inheritance
Drawbacks of inheritance
Inheritance is not without its own set of drawbacks. If inheritance is applied without due consideration problems can arise. In some situations it can:
- Reduce the comprehensibility of code.
- Make maintenance harder.
- Make further development harder.
- Reduce reliability of code.
- Reduce overall reuse.
Conclusion
<EDIT THIS> We have considered the benefits and drawbacks of inheritance within an object oriented programming language. We have challenged the general perception that inheritance is by its very nature always good and have considered when it should and should not be used. We have re-assessed compositional reuse and made the case that it is as important, in an object oriented language, as inheritance in order to achieve the maximum possible reuse. We can therefore provide a summary of our findings that can be used as a set of guiding principles for object oriented development: · Avoid code dependency except on published protocol. · For structural inheritance direct extension is fine.