Abstract Class

• A method which has only method declaration and no definition is called as "Abstract method".
• Abstract method should be always declared with "abstract" keyword.
• A class which is declared with "abstract" keyword is called as abstract class.

           ex:                                              abstract class Vijay{

  abstract public void blog();

}

• A method which has both method declaration and definition is called "concrete method".
• Class which contains only concrete methods is called as "contact class".

An abstract class may contain

(i) concrete methods

(ii)abstract methods

(iii) both concrete and abstract methods

• It is not possible to create object of an abstract class because the method don't have body or definition.
• We can create reference variable of an abstract class, because to perform upcasting and downcasting for achieving runtime polymorphism.

          ex: Vijay v;

• If a class is extending an abstract class then the subclass should override the abstract methods present in abstract class.
• If a class is not overriding the abstract methods of superclass then the subclass also becomes abstract.
• Abstract methods cannot be declared as static.
• Abstract methods cannot be declared as private.
• Abstract methods cannot be declared as final because we can inherit final methods but we can't override it.