Object oriented Lecture Slide -Abstraction MAH.pptx

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OOP: Lecture 09
Abstraction in Java
E n g r . A r i f H a s a n C h o w d h u r y, A s s i s t a n t P r o f e s s o r ,
D e p t . o f C S E , S o u t h e r n U n i v e r s i t y B a n g l a d e s h
E m a i l : a r i f h a s a n @ s o u t h e r n . a c . b d

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What is Abstraction in Java?
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• Abstraction is the process of hiding certain details and showing only essential information to the user.
• hiding the implementation details from the user.
• User will have the information on what the object does instead of how it does it.
Ways to achieve Abstraction
There are two ways to achieve abstraction in java
• Abstract class (0 to 100%)
• Interface (100%)

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abstract class
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 class contains the abstract keyword in its declaration is
known as abstract class.
 Abstract classes may or may not contain abstract
methods, i.e., methods without body ( public void
get(); )
 if a class has at least one abstract method, then the
class mustbe declared abstract.
 If a class is declared abstract, it cannot be instantiated.
 To use an abstract class, you have to inherit it from
another class, provide implementations to the abstract
methods in it.
 If you inherit an abstract class, you have to provide
implementations to all the abstract methods in it.

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Syntax and Example
Example
abstract class A
{
abstract void callme();
public void show()
{
System.out.println("this is non-abstract method");
}
}
class B extends A
{
void callme()
{
System.out.println("Calling...");
}
public static void main(String[] args)
{
B b = new B();
b.callme();
b.show();
}
Output:
calling...
Syntax:
abstract class class_name {
Abstract Method
Non Abstact Method
}

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Example: abstact class with non abstract method
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abstract class A
{
abstract void callme();
public void show()
{
System.out.println("this is non-abstract method");
}
}
class B extends A
{
void callme()
{
System.out.println("Calling...");
}
{
B b = new B();
b.callme();
b.show();
}
Output:
calling... this is non-abstract method
Abstraction using abstract class:
abstract class Vehicle
{
public abstract void engine();
}
public class Car extends Vehicle {
public void engine()
{
System.out.println("Car engine");
// car engine implementation
}
{
Vehicle v = new Car();
v.engine();
}
}
Output:
Car engine

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• Can we create object of abstract class?

Object oriented Lecture Slide -Abstraction MAH.pptx

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