Polymorphism,Abstraction,Overloading,Overriding,Enum Type,Java Servlets

# Java – Polymorphism:

ð  Polymorphism is the ability of an object to take on many forms.

ð  The most common use of polymorphism in OOP occurs when a parent class reference is used to refer to a child class object.

ð  This is possible because all objects of base class object of its super class.

ð  It helps to prevent the code from becoming more complex and cumbersome (unmanageable) by allowing us to make different implementations of related functionalities under one name object or method.

ð  It is capability of an action or method to do different things base on the object that it in upon.

ð  Overloading and Overriding are two type of polymorphism.

# Java – Abstraction:

ð  In OOP it means that ability to make a class abstract.

ð  An abstract class is one that cannot be instantiated. All other functionality of the class still exists, and its fields, methods, and constructors are all accessed in the same manner.

# Abstract Methods:

ð  If you want a class to contain a particular method but you want the actual implementation of that method to be determined by child classes, you can declare the method in the parent class as abstract.

ð  An abstract method consists of a method signature, but no method body.
Declaring a method as abstract has two results:

ð  The class must also be declared abstract. If a class contains an abstract method, the class must be abstract as well.

ð  Any child class must either override the abstract method or declare it abstract.

Overloading and Overriding:

Overloaded Method	Overriding Method
1) Method with same name, same signature.	1) Method has the same name, same signature, same return type as a super class method, also same access modifier but not be more restrictive then super class method. If super class method is private then cannot be override.
2) Different number of parameters or different type of parameter, different returns type.	2) Method that one redefined with an inherited or subclass.
3) It can be exist in the same class or another class.
4) It’s a compile type polymorphism.	3) It’s a Runtime polymorphism
5) exp: -void sum(int a,int b){} it can be overloaded as- -void sum(int a,int b,int c){} - void sum(int a,string b){} - void sum(string a,string b){} etc…	4) exp: Class father{          void hand(int h){          smoking;         } } class child extends father{      void hand(int h){      drinking;      } } }

#Constructor:

ð  It has the same name as the name of class to which it belongs.

ð  It has no return type, it does not return anything.

ð  May (argumented) or may not (default cons.) include arguments.

# Enum Type :

#varargs:

# Autoboxing :

ð  Auto boxing is a capability to convert or cast between object wrapper and its primitive type(int<>Integer).

ð  int => Integer =Boxing

ð  Integer => int = Unboxing

# wrapper Class :

ð  In java wrappers are class that wrap up primitive values in classes that offer utility methods to manipulate the values.Exp: Integer,Boolean Class etc.

# What is Java Servlets?

ð  Servlets are server side components that provide a powerful mechanism for developing server side programs.

ð  A servlet is a Java programming language class used to extend the capabilities of servers.

ð  Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by Web servers.

ð   init(),service()[doGet() or doPost()],destroy()