Lecture 4 inheritance , polymorphism.pptx
- 1. Inheritance
- 2. Introduction • Generalisation & Inheritance • What happens when inheritance takes place? • Multiple Inheritance • Abstract Classes
- 3. Generalisation(1) • Also known as inheritance Car Lorry Vehicle
- 4. Generalisation(2) Student Lecturer Module * 1 * * teaches attends StudNumb Title ModNumb Person Name
- 5. Inheritance Example(1) • Consider these objects Red Car Yellow Truck Blue Car Green Truck
- 6. Inheritance Example(2) • We can see that there are two car objects and two truck objects • Therefore two classes ... Car Truck
- 7. Common & Different Data • But Cars and Trucks have similar attributes (and functions) ... Car Truck TopSpeed Length Weight Colour BootVolume TopSpeed Length Weight Colour FlatBedSpace
- 8. Data Allocation Car Vehicle Truck float BootVolume float FlatBedSpace float TopSpeed float Length float Weight String Colour
- 9. Superclasses and subclasses • A class defined in terms of another. SuperClass Subclasses
- 10. An Inheritance Tree Vehicle Car Truck SportsCar Hatchback Articulated Fixed Wheel Base 2 axle 3 axle
- 11. Data Attribute Location(1) Vehicle Truck Vehicle Truck float length float weight float length float weight float maximumLoad
- 12. Data Attribute Location(2) Truck Fixed Wheel Base Truck float length float weight float maximumLoad FixedWheelBase float length float weight float maximumLoad
- 13. Data Attribute Location(3) Fixed Wheel Base 2 axle 3 axle FixedWheelBase float length float weight float maximumLoad 3 axle float length float weight float maximumLoad int axleLoad
- 14. Inheritance Tree 3 axle Fixed Wheel Base Truck Vehicle A 3 axle truck is a Fixed WheelBase is a truck is a vehicle
- 15. Inheriting Data and Operations • If the data or operation is missing in class • try to inherit from higher level class. • If the data or operation is present in class • then use from this class.
- 18. Abstract Classes(1) • Higher up inheritance hierarchy, classes become more general. • They can become more abstract. • An abstract class has no object instances.
- 19. Abstract Classes(2) Vehicle WaterVehicle LandVehicle AirVehicle Glider Plane Helicopter Balloon Rocket Abstract Classes
- 20. Conclusion • Generalisation & Inheritance • What happens when inheritance takes place? • Multiple Inheritance • Abstract Classes