Lecture 2 Inheritance And Polymorphism

Inheritance and Polymorphism
Prepared by: Prof. Irysh Paulo R. Tipay, MSCS

Quote for the Day
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“That's the thing about people who think they hate computers. What they really hate is lousy programmers.” ― Larry Niven

Recap!
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What you already know…
In OOP, EVERYTHING is an OBJECT
A Class is a blueprint/model used for creating
Objects
An Object is an instance of a Class
Both Objects and Classes have an attribute and behaviour A class should have at least one Constructor.
A Constructor is used to set the default values of the attributes
A Class Diagram is a UML which is basically a graphical representation of a class

Inheritance
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This is a way of relating 2 or more classes.
This is the idea of passing down the attributes and behaviours of the super class to the sub class. Super class – (base class,
SUPER CLASS parent class)

Sub class – (child class,
CLASS
derivedSUB class) This is the symbol used to show inheritance

Inheritance
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Inheritance is an “is-a” relationship.
Student is a Person
Teacher is a Person

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Cat is an Animal

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Dog is a Fruit

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Grape is a Fruit

Inheritance
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Java supports single inheritance, meaning a super class can have multiple sub classes, but a sub class can only have one super class. SUPER CLASS

SUB CLASS

SUB CLASS

SUB CLASS

Inheritance
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A sub class can be a super class of another class. CLASS A

CLASS B

CLASS C

Inheritance
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Observe…
VEHICLE

CAR

Inheritance
Vehicle
- String color
- String bodyNumber
-String
numberOfWheels
+Vehicle()
+void accelerate();
+ void brake();

Car
- String plateNumber
- String mileage
+Car()
+void playMusic();
+ void enableGPS();

Car myCar = new Car( ); myCar.accelerate( );

In this Example, the Car class is able to inherit all the members of the
Vehicle class EXCEPT for its private members. The “extends” keyword public class Vechicle{ private String color; private String bodyNumber; private String numberOfWheels; public Vehicle(){ color = “blue”;
public