• Core
• Introduction
• Java Fundamentals
• JDK File Structure
• Development
• Operators and Assignments
• Flow Control
• Declarations and Access Modifiers
• Garbage Collector
• Oops Concepts
• Java Object Class
• Inner classes
• Java Package
• Java.lang package
• Java.io package
• Exception handling
• Multithreading
• Regular Expressions
• Enumerations
• Internationalization
• Assertions
• Collection Framework  
• Generics
• JDBC
• Features of Java 5

Enumeration (enum)

We can use enum to define a group of named constants

Example :
1) enum month
{
JAN,FEB,MAR, ......DEC;
}
By using enum we can define our own datatype
Enum concept introduced in 1.5v
When compared with old language enum, java's enum is more powerfull.

Internal Implementation of enum:-
1.Enum concept internally implemented by using class concept.
2.Every enum constant is a reference variable to enum type object.
3.Every enum constant is always public static final by default.

Declaration and usage of enum:-

We can declare enum either with in the class or outside of the class but not inside a method.
If we are trying to declare enum with in a method we will get compile time error.

Note :
enum type must not be local
If we declare enum outside the class the applicable modifiers are public,default, strict fp
If we declare enum with in a class the applicable modifiers are public,default,strictfp,private,protected,static.

Enums switch statement:-
Until 1.4v the allowed datatype for switch arguments are bye,short,char,int.
But from 1.5v onwards to above the corresponding wrapper classes Byte,char,integer,enum type also allowed

Enum vs Inheritance:-
Every enum in java is direct child class of java.lang.enum
As every enum is always extending java.lang.enum there is no chance of extending any other enum(because java wan 't provide support for multiple inheritance)
As every enum is always final implicitly we can 't create child enum for our enums.
Because of above reasons we can conclude inheritance concept is not applicable for enums explicitly.
But enum can implements any no. of interface at a time.

Example:
1) Enum x (2) enum x extends java.lang.enum
{
{
Enum y extends x //wrong
{
}
//wrong }

C.E:-
Cannot inherit form final x
Enum types not extensible
(1) Enum x (4)class x
{
{
//write
}
} //wrong
class y extends x enum y extends x
{
{
}
}
C.E1: cannot inherit from final x
C.E2: enumtypes are not extensible
(5)
Interface x
{
}
Enum y implements x
{
//write }

Java.lang.Enum:-
Every enum in java is always direct child class of java.lang.enum.class.
The power of enum is inheriting from this class only to our enum class.
It is an abstract class and direct child class of object class.
This class implements comparable and serializable interface. Hence every enum in java is byt default serializable and comparable.

Values() method:-
With in the enum the orders of constants is important we can specify its orders by using original value.
We can find ordinal value of enum constants by using ordinal method.

public int ordinal();
Ordinal value is zero-based

Enum class Constructors and speciality of java enum:-
When compared with old languages enum,Java enum is more powerful because in addition to constants we can take variables, methods, constructors etc.. Which may not possible in old language this extra facility is due to internal implementations of enum concept which is class based.
Inside enum we can declare main() methods and hence we can invoke enum class directly from command prompt.

Inside enum without having constants we can 't take any extra members, but empty enum is always valid

Enum class Constructors:-
With-in enum we can take constructors also.
Enum class constructors will be executed automatically at the time of enum class loading. Hence enum constants will be created at the time of class loading only. We can 't invoke enum Constructors explicitly

We can 't create objects of enum explicitly and hence we can 't call constructors directly.
Fruits b=new Fruits(); X or wrong
C.E:
Enumtypes may not be instantiated

Within the enum we can take instance and static methods but we can 't to take abstract methods.
Every enum constant represents an object hence what ever the methods we can apply on normal java object we can apply those on enum methods also.

enumVsEnum VS Enumeration:-
enum:-
It is a keyword which can be used to define a group of named constants.

Enum:-
It is a class parent in java.lang package which acts as a base class for all java enums.

Enumeration:-
It is an interface present in java.utilpackage,which can be used for retrieving objects from collection one by one.