2. Objectives
On completion of this period, you would be able to
learn
• Inheritance
• Inheritance basics
• Visibility modifiers
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3. Recap
In the previous lesson, you have learnt
• Command-line arguments
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4. 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
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5. 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
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6. 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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7. 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
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8. 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
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9. 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
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10. 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
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11. 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
}
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12. Example
class A {
int i,j;
void showij() {
System.out.println(“ i and j :” + I + “ “ + j);
}
}
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13. 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));
}
}
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14. 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();
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15. 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();
}
}
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16. 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
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17. 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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18. Summary
• In this class, we have discussed
• Inheritance
• Inheritance principle
• Inheritance syntax
• Super class
• Sub class
• Public, private and protected modifiers
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19. Quiz
1. A class which is inherited from other class is called
a) Super class
b) Sub class
c) Anonymous class
d) Object
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20. Quiz contd...
2. A class which used to inherits a class is called
a) Sub class
b) Super class
c) Anonymous class
d) object
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21. Quiz contd...
3. What is the keyword used to inherit a class
a) create
b) new
c) this
d) extends
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22. Quiz contd...
4.Public variables volatile the principle of
a) Polymorphism
b) Encapsulation
c) Inheritance
d) Overloading
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23. Quiz Contd..
5. Variables and methods declared with following
are inherited
a) private
b) public
c) protected
d) abstract
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24. 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
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