CS112-2012S-10 Inheritance 110-0: Classes• Want to create a bunch of classes for a real estate program• Apartment Building:• Square Footage• Number of floors• Number of units10-1: Classes• Want to create a bunch of classes for a real estate program• Private House• Square Footage• Number of floors• Number of bedrooms10-2: Classes• Want to create a bunch of classes for a real estate program• Office Building• Square Footage• Number of floors• Number of Elevators10-3: Classes• Several data members (and methods) that are shared across all building types:• Square footage• floors• We could duplicate these variables in all of our classes (so that the House class and Office class and Apartmentclass would all contain a definition of an instance variable for Square Footage, for example)• What are potential problems with this approach?10-4: ClassesIt would be nice if we didn’t need have so much repitition:• Class that describes a building• Contains Square footage, number of floors, etc• (Features common to all buildings)• Class that describes an apartment building• Autmatically has everything in a generic building• Extra instance variables / methods that are particular to apartments10-5: InheritaceCS112-2012S-10 Inheritance 2• Add “extends ¡classname¿” to class defition• class Apartment extends Building { ... }• Defines an “is-a” relationship• Apartment is a building• Defines a superclass/subclass relationship• Building is the superclass• Aparment is the subclass10-6: Inheritace• Add “extends ¡classname¿” to class defition• class Apartment extends Building { ... }• Subclass inherits all of the methods / data from the superclass.• Examples from code10-7: Adding Constructors• Superclasses and subclasses can have constructors• Subclass can call the constructor of the superclass with the “super” keyword• We’ll find more uses for the super keyword later• If you call the constructor of a subclass from a superclass, you need to do it first• Show examples• How would you do the same thing without using “super”?10-8: Super & Constructors• If you do not call the constructor of the superclass explicitly, then the default (no parameter) version of theconstructor is called automatically at the beginning of the constructor• Each class takes care of itself• Don’t need to worry (too much) about the inner workings of a superclass when writing a subclass• Just concentrate on the new stuff(examples)10-9: Access control• public: Anyone use it• protected: Only subclasses can use it• private: No one but the original class can use it.Examples10-10: Overriding MethodsCS112-2012S-10 Inheritance 3class SuperClass {void print() {System.out.println("Message from SuperClass");}}class SubClass extends SuperClass {void print() {System.out.println("Message from SubClass");}}SuperClass sup = new SuperClass();SubClass sub = new SubClass();sup.print();sub.print();10-11: Using Superclass SuperClass {void print() {System.out.println("Message from SuperClass");}}class SubClass extends SuperClass {void print() {System.out.println("Message from SubClass");super.print();}}10-12: Get your Fingers Dirty• Define a Class Vehicle, which has the protected integer instance variable numWheels. Also, add public accessor (get/set) methods for numWheels, and a constructor that takes as an input parameter the number of wheels.• Define a Class Bicycle, subclass of Vehicle, which has the protected integer instance variable gears. Add public accessor (get/set) methods for gears, and a constructor that takes as an input parameter the number of gears.The constructor should set the number of wheels to 2 (by calling super)• Define a Class Car, subclass of Vehicle, which has the protected double instance variable horsepower. Add public accessor (get/set) methods for horsepower, and a constructor which takes as an input parameter thehorswpower, and set the number of wheels to 4 (by calling super)• Define a Class Truck, subclass of Car, which has the protected double instance variable payloadVolume. Add public accessor for payloadVolume, and a constructor that takes 2 parameters, horsepower and payload volume.Create a main program that instantiates one of each class, and then uses set methods to make the truck a 3 wheeled, 0.5 horsepower truck with a payload volume of
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