Basics of inheritance .22

Basics of Inheritance

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1

Objectives

On completion of this period, you would be able to
learn

• Inheritance
• Inheritance basics
• Visibility modifiers


Recap

In the previous lesson, you have learnt
• Command-line arguments


Inheritance

• Inheritance is process by which one class gets the

properties from an existing class
• Object-oriented programming allows classes to inherit

• Commonly used state and behavior from other
classes
• Inheritance is one of the principles of object oriented

programming
• Benefit of inheritance is the software reuse


Inheritance Basics
• Inheritance allows a software developer to
derive a new class from an existing one
• The existing class is called the parent class or
superclass
• The derived class is called the child class or
subclass
• Creates an is-a relationship
The subclass is a more
specific version of the
original

5

Inheritance Basics contd..

• In Java a class that is inheriting is called a super class

• A class that is inherited is called sub class

• Sub class is a specialized version of super class

• Sub class inherits all instance variables and methods

defined by super class and can have its own elements
• In Java one direct superclass, and each superclass has
the potential for an unlimited number of subclasses

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Inheritance Basics contd..

Book
• In Fig. 22.1 Book is the existing class
• Dictionary and Novel are
Dictionary Novel
sub classes of Book
• Mystery and Romance are
sub classes of Novel Mystery Romance

Fig 22.1 Book inheritance

7

Discussion
• What are the super and
sub classes in Fig. 22.2
• Super class Bicycle
• Sub classes
MountBike
RoadBike
TandemBike
Fig. 22.2 Bicycle example


Discussion contd..
Object

Class A Class D

Class E
Class B Class C

Fig. 22.3 Another example

• What are the super and sub classes in Fig. 22.3

• Super classes Object, Calls A, Class D
• Sub classes Class A, Class B, Calss C, Class C, Class D

Syntax
• To inherit a class from another class use keyword

“extends”
Syntax

class subclass-name extends superclass-name {
( body of the class )
}
If a class B is inherited from class A
class B extends A // A inherits B
// Super class –A, Subclass- B

Syntax contd...

• Consider the above Bicycle example

• Using the above syntax the inheritance can be shown as
below

class MountainBike extends Bicycle {
// new fields and methods defining a mountain bike would go here
}


Example

class A {
int i,j;
void showij() {
System.out.println(“ i and j :” + I + “ “ + j);
}
}


Example contd..

class B extends A {// creating subclass B from super class A
int k;
void showk() {
System.out.println(“ k:” +k);
}
void sum() {
System.out.println(“ i + j + k:” ( i+j+k));
}
}

Example contd..

class SimpleInheritance {

public static void main( String args[]) {
A superOb = new A();
B subOb = new B();
superOb.i = 10;// super class may be used by itself
superOb.j = 20;
System.out.println( “ Contents of superOb:”);
superOb.showij();
System.out.println();

Example contd..
subOb.i = 7; // sub class has access to all public members
subOb.j = 8; // of its super class
subOj.k = 9;
System.out.println(“ Contents of subOj:” );
subOb.showij();
subOj.showk();
System.out.println();
System.out.println( “ sum of i,j and k in subOb:”);
subOb.sum();
}
}

Output

Contents of superOb :
i and j : 10 20
Contents of subOb :
i and j : 7 8
k:9
sum of I,j and k in subOb :
i + j + k: 24


Some Inheritance Details

• An instance of a child class does not rely on an instance
of a parent class
• Hence we could create a Dictionary object without
having to create a Book object first

• Inheritance is a one-way street
• The Book class cannot use variables or methods
declared explicitly in the Dictionary class

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Summary
• In this class, we have discussed
• Inheritance
• Inheritance principle
• Inheritance syntax
• Super class
• Sub class
• Public, private and protected modifiers


Quiz

1. A class which is inherited from other class is called
a) Super class
b) Sub class
c) Anonymous class
d) Object


Quiz contd...

2. A class which used to inherits a class is called
a) Sub class
b) Super class
c) Anonymous class
d) object


Quiz contd...

3. What is the keyword used to inherit a class

a) create

b) new

c) this

d) extends


Quiz contd...

4.Public variables volatile the principle of
a) Polymorphism
b) Encapsulation
c) Inheritance
d) Overloading

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Quiz Contd..

5. Variables and methods declared with following
are inherited
a) private
b) public
c) protected
d) abstract


Frequently Asked Questions
• What is inheritance ?
• Mention the key word to inherit a class from others
• What is super class ?
• What is sub class ?
• Write about public modifier
• Write about private modifier
• What protected modifier
• Write a program in Java using modifiers
• Write a program in Java for inheriting a class from others


Basics of inheritance .22

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Basics of inheritance .22