In this session you will learn: Encapsulation Inheritance For more information, visit: https://www.mindsmapped.com/courses/software-development/java-developer-training-for-beginners/

1. Java/J2EE Programming Training
Java Inheritance

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Agenda
• Encapsulation
• Inheritance

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• Implement encapsulation
• by marking the field as private.
• by marking the member function as private.
Encapsulation

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• avoids reinventing the wheel
• promotes code reusability
• derives a new class from the existing class
• use the existing features
• enhance the existing features
• add new features.
• Existing class is called as “base class”
• new class derived from existing class is called as “Child class”
Inheritance

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• child class will have all the features from the parent class
• plus it will have its own additional features
• additional features:
• new member variable ;
• new member functions
• What can you access in child class from parent class
• non private member variables
• non private member variables can be access via setter and getter
methods of parent class.
• non private member functions
• What can you do in Child class
• access non private data from parent class directly.
• inherited methods can be accessed directly.
• declare new methods in child class.
• override parent class methods in child class.
Inheritance

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Sms
+ String to
+ String text
+ void sendSms()
PictureSms
+ String to
+ String text
+ String pic
+ void sendSms()
+void sendPicSms()

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Rectangle
+ int length
+ int breadth
+ void area()
Cuboid
+ int length
+ int breadth
+ int height
+ void surfaceArea()
+void volume()

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Student
String username
String passwd
String course
Int score
login()
logoff
writeExam()
viewResult
Employee
String username
String passwd
String desig
Int salary
login()
logoff
evaluate()

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Student
String username
String password
String course
Int marks
Login()
Logoff()
takeExam()
Employee
String username
String password
String desig
Int salary
Login()
Logoff()
evaluate()
User
String username
String password
Login()
Logoff()

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Question
+ String question
+ String optionA
+ String optionB
+ char answer
+ void addQuestion()
+ void deleteQuestion
ImageQuestion
+ String question
+ String optionA
+ String optionB
+ char answer
+ Image img
+ void addQuestion()
+ void deleteQuestion
+ void addImage()
VideoQuestion
+ String question
+ String optionA
+ String optionB
+ char answer
+ Video video
+ void addQuestion()
+ void deleteQuestion
+ void addVideo()

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Constructors….revisited
• Constructor are not inherited
• When a child class object is created,
• derive class constructor invokes its immediate super class constructor,
all the way up the hierarchy.
• How can a child class constructor call its parent class constructor.
• using super keyword

12. How constructors are invoked Rectangle
+ int length
+ int breadth
+ void area()
Cuboid
+ int length
+ int breadth
+ int height
+ void surfaceArea()
+void volume()
Cuboid c = new Cuboid();
Rectangle
+ int length
+ int breadth
+ void area()
length = 0
breadth= 0 Cuboid
+ int length
+ int breadth
+ int height
+ void surfaceArea()
+void volume()
height = 0

13. Cuboid c= new Cuboid() class Rectangle
{
public int length;breadth;
public Rectangle()
{
length = 0;
breadth =0;
}
}
class Cuboid
{
//private int length;breadth;
public int height;
public Cuboid()
{
super();
height = 0;
}
}
length=0
breadth=0
height =0
call to super is
inserted by the
compiler implicitly f
default constructor

14. Cuboid c= new Cuboid(10, 20,30) class Rectangle
{
public int length;breadth;
public Rectangle(int l, int
b)
{
length = l;
breadth =b;
}
}
class Cuboid
{
//private int length;breadth;
public int height;
public Cuboid(int l, int b,int
h)
{
super(l, b );
height = h;
}
}
length=10
breadth=20
height =30
call to super is explicit

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Super
• super keyword is used to call immediate parent class constructor
• should be the first statement of the constructor
• If the programmer does not provide call to super(), then the compiler
inserts the call to super.
• programmer must call super() explicitly for constructor with arguments.

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Thank You