For Abstract class
you should have knowledge of Abstract
methods in java. An Abstract method
is nothing but a simple method in java but without body or say it doesn’t have
statements into it. It only contains the declaration of method
i.e. having
modifier, return type, name and parameters.
So, now we can say the class having Abstract methods should be declared as Abstract and so it is called Abstract
class.
An Abstract class
is never instantiated or we can say we cannot create object of Abstract class. Although it does not
provide 100% abstraction because it can also have methods with definition.
Syntax :
abstract class class_name { }
Some properties of Abstract method:
Method that are declared without any body within an abstract
class are called abstract method.
The method body will be defined by its subclass. Abstract method can never be final and static. Any class that
extends an abstract class must implement all the abstract methods declared by the super class.
Syntax :
abstract return_type function_name (); //No definition
Example of Abstract class :
abstract class A
{
abstract void callme();
}
class B extends A
{
void callme()
{
System.out.println("this is
callme.");
}
public static void main(String[] args)
{
B b = new B();
b.callme();
}
}
OUTPUT :
this is
callme.
When to use Abstract Methods &
Abstract Class?
Abstract
methods are usually declared where two or more
subclasses are expected to do a similar thing in different ways through
different implementations. These subclasses extend the same Abstract class and provide different
implementations for the abstract methods.
Abstract
classes are used to define generic types of
behaviors at the top of an object-oriented programming class hierarchy, and use
its subclasses to provide implementation details of the abstract class.
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