![Example – Specialization
(Restriction)
Person
age : [0..100]
…
Adult
age : [18..100]
…
setAge( a )
…
setAge( a )
…
age = a
If age < 18 then
error
else
age = a](https://image.slidesharecdn.com/lec5oop-231015154917-36c3da3a/85/Lec5_OOP-pptx-14-320.jpg)
Lec5_OOP.pptx
- 2. Recap – Inheritance ►Derived class inherits all the characteristics of the base class ►Besides inherited characteristics, derived class may have its own unique characteristics ►Major benefit of inheritance is reuse
- 3. Concepts Related with Inheritance ►Generalization ►Subtyping (extension) ►Specialization (restriction)
- 4. Generalization ►In OO models, some classes may have common characteristics ►We extract these features into a new class and inherit original classes from this new class ►This concept is known as Generalization
- 9. Sub-typing & Specialization ►We want to add a new class to an existing model ►Find an existing class that already implements some of the desired state and behaviour ►Inherit the new class from this class and add unique behaviour to the new class
- 10. Sub-typing (Extension) ►Sub-typing means that derived class is behaviourally compatible with the base class ►Behaviourally compatible means that base class can be replaced by the derived class
- 13. Specialization (Restriction) ►Specialization means that derived class is behaviourally incompatible with the base class ►Behaviourally incompatible means that base class can’t always be replaced by the derived class
- 14. Example – Specialization (Restriction) Person age : [0..100] … Adult age : [18..100] … setAge( a ) … setAge( a ) … age = a If age < 18 then error else age = a
- 15. Example – Specialization (Restriction) IntegerSet … NaturalSet … add( elem ) … add( elem ) … add element to the set If elem < 1 then error else add element to the set
- 16. Overriding ►A class may need to override the default behaviour provided by its base class ►Reasons for overriding Provide behaviour specific to a derived class Extend the default behaviour Restrict the default behaviour Improve performance
- 17. Example – Specific Behaviour Shape color vertices draw move setColor Circle radius draw computeArea Line length draw Triangle angle draw computeArea
- 18. Example – Extension Window width height open close draw DialogBox controls enable draw 1- Invoke Window’s draw 2- draw the dialog box
- 19. Example – Restriction IntegerSet … NaturalSet … add( elem ) … add( elem ) … Add element to the set If elem < 1 then give error else Add element to the set
- 20. Example – Improve Performance ► Class Circle overrides rotate operation of class Shape with a Null operation. Shape color coord draw rotate setColor Circle radius draw rotate
- 21. Abstract Classes ►An abstract class implements an abstract concept ►Main purpose is to be inherited by other classes ►Can’t be instantiated ►Promotes reuse
- 22. Example – Abstract Classes Teacher Doctor Student ►Here, Person is an abstract class Person name age gender eat walk
- 23. Example – Abstract Classes Bus Truck Car ►Here, Vehicle is an abstract class Vehicle color model accelerate applyBrakes
- 24. Concrete Classes ►A concrete class implements a concrete concept ►Main purpose is to be instantiated ►Provides implementation details specific to the domain context
- 25. Example – Concrete Classes ►Here, Student, Teacher and Doctor are concrete classes Teacher Doctor Student program studyYear study heldExam Person
- 26. Example – Concrete Classes • Here, Car, Bus and Truck are concrete classes Bus Car Vehicle Truck capacity load unload