Polymorphism, Abstract Class, Abstract Method and Final Keyword in Java

Polymorphism,

•  Abstract Class,  
• Abstract Method 
•  Final Keyword

Abstract Class 

• Abstract class is declared with abstract key word.
• The class contains abstract methods.
• Abstract methods are declared inside abstract class.
• Abstract methods by thare declared with abstract key word.
• Abstract methods are defined e child class  
• Abstract class cannot have any object.
• The child class of the abstract class must override all the abstract methods of the parent class.
• If the child class does not override any abstract method of the parent class it should also be declared abstract.
• Reference variable can be declared of abstract class.
• Abstract class may have abstract and concrete methods.
• Non abstract methods are also called concrete methods.
• All the members of the abstract class can be accessed only through the object of the child class.

Example #1 Abstract Class 

Abstract Class 

• It allows a super class to specify methods that will be common to all its derived classes and does not provide any definition of these methods.
• It allows subclasses to define the specific implementation of some or all of those methods.
• Its another way java implements one interface, multiple methods aspect of polymorphism.
• By combining inheritance with overridden methods ,a super class can define the general form of the methods that will be used by all of its subclasses.
• This is also called run time polymorphism.

Polymorphism 

• The object referred by the reference variable of the super class is determined at run time.
• The binding of object to the overridden method is performed at run time.
• The reference variable of the parent class is binded  dynamically to different methods at run time.Therefore its called dynamic/late binding.

Final Keyword

lThe class declared with final key word cannot be inherited.

l The method declared with final keyword cannot be overridden

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