principles of computer programming (using java) chapter 10 subclasses
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Principles of Computer Programming(using Java)
Chapter 10 Subclasses
Haidong XueSummer 2011, at GSU
Content• Inheritance• Overriding• Polymorphism• The “Object” class
Inheritance
• What is inheritance?• What are the advantages of inheritance in
Java?• How to make a class in Java using inheritance?• E.g.:
– TestInheritance.java, Vehicle.java, Car.java, Bike.java
Inheritance
Car
Data: speed, weight, gas amount, size of tires
Actions: show speed, show weight, accelerate, brake, add gas, show tire size
Inheritance
Bike
Data: speed, weight, size of tires, size of pedals
Actions: show speed, show weight, accelerate, brake, show tire size, show pedal size
Inheritance
Car
Data: speed, weight, gas amount, size of tires
Actions: show speed, show weight, accelerate, brake, add gas, show tire size
Bike
Data: speed, weight, size of tires, size of pedals
Actions: show speed, show weight, accelerate, brake, show tire size, show pedal size
Inheritance
Car Bike
Vehicle
Data: speed, weight, size of tires
Actions: show speed, show weight, accelerate, brake, show tire size
Data: gas amount
Actions: add gas
Data: size of pedals
Actions: show pedal size
extends
• TestInheritance.java• Vehicle.java• Car.java• Bike.java
Inheritance
Overriding
• If a method in the subclass has the same signature of a method in the superclass, the method in the superclass is hided and overridden.
• E.g.:– TestOverriding.java– Vehicle.java, Car.java, Bike.java
Polymorphism
• An ability of a programming language;• an instance of a subclass can take the place
of an instance of any of its superclasses;• if an object variable of the superclass points to
a subclass object, when calling an overridden method, the method of the subclass will be called.
The punch game
• InstructorsInCSC2310.java
The Object class
• What is Object class?• A rule: all the classes have to have a superclass.• The Object class is the default superclass.• What are the advantages?
– One type for all;– Some common method for all the objects, like toString().
The bonus assignment
• Worth: 10 points in the final grade• Develop a program to play Texas Holdem
Poker
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