basics of inheritance .22
TRANSCRIPT
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Basics of Inheritance
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Objectives
On completion of this period, you would be able to learn
• Inheritance• Inheritance basics• Visibility modifiers
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Recap
In the previous lesson, you have learnt • Command-line arguments
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• 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
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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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• 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..
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• In Fig. 22.1 Book is the existing class• Dictionary and Novel are
sub classes of Book• Mystery and Romance are sub classes of Novel
Book
NovelDictionary
Mystery Romance
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Fig 22.1 Book inheritance
Inheritance Basics contd..
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Fig. 22.2 Bicycle example
Discussion
• What are the super and sub classes in Fig. 22.2
• Super class
• Sub classes
Bicycle
MountBike RoadBike TandemBike
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Object
Class A Class D
Class B Class CClass E
Fig. 22.3 Another example
Discussion contd..
• What are the super and sub classes in Fig. 22.3
• Super classes
• Sub classes
Object, Calls A, Class D
Class A, Class B, Calss C, Class C, Class D
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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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• 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
}
Syntax contd...
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Example
class A {
int i,j;
void showij() {
System.out.println(“ i and j :” + I + “ “ + j);
}
}
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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..
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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..
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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();
} }
Example contd..
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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
Output
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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
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Quiz
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1. A class which is inherited from other class is called a) Super classb) Sub classc) Anonymous classd) Object
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Quiz contd...
2. A class which used to inherits a class is called a) Sub classb) Super classc) Anonymous classd) object
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3. What is the keyword used to inherit a class
a) create
b) new
c) this
d) extends
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Quiz contd...
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4.Public variables volatile the principle ofa) Polymorphismb) Encapsulationc) Inheritance d) Overloading
Quiz contd...
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Quiz Contd..
5. Variables and methods declared with following are inherited
a) private b) public c) protected d) abstract
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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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