enum in Java (Enumeration)- Introduction

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Java Enums Introduction:-

1. According to the java naming conventions, if you have any constant variable, it must be declared in the UPPERCASE.

2. All the constants should be represented with "public static final "as follows

public static final String AVAILABLE="User is available";

public static final String BUSY="User is busy";

public static final String IDLE="User is idle";

3. Java is a strictly typed programming language, the above example will reduce the typedness as it is representing a different data types.
public static final String AVAILABLE="User is available";

public static final int BUSY=0;

public static final boolean IDLE=true;

4. public static final String AVAILABLE="User is not available";

public static final int BUSY=0126262;

public static final boolean IDLE=false;

In the above approach, if we access the constant variables than the values of the constants variables are displayed. However the values may or may not have the meaningful messages with respect to the constant variables.

To overcome all the above problems we are actually going for Java Enums

Enums :-

An enum is a special "class" that represents a group of constants(unchangeable variables, like final variables).

To create an enum, we have to use the "enum" keyword and separate the constants with commas. They should be represented in the upper case letter.

Normal Approach of defining the constants in class

class User_Status {
public static final String AVAILABLE="User is not available";

public static final int BUSY=0126262;

public static final boolean IDLE=false;

}

Defining the constants by using Enums:-

enum User_Status
{
AVAILABLE,
BUSY,
IDLE;
}

Syntax :-
[Access Modifer] enum Name{

//Set of constants

}

Points to be remembered :-

1. All the variables inside the enum type are constant variables and they are public static final by default.

2. All the constant variables are by default of the same enum type not required to provide any explicit data type.

3. All constant variables named constant by default, if we access constant variables name of the constant itself will be displayed, not the value.

Users Code:-
enum User_Status
{
AVAILABLE,
BUSY,
IDLE;
}

Compiler code:-
public static final User_Status AVAILABLE;
public static final User_Status BUSY;
public static final User_Status IDLE;
public static User_Status[] values();
static {};
}

1. Please be informed that you can define the enum, outside the class or inside the class but not inside the methods.

2. You cant create an object for the enum. It means you cant instantiate by using the new keyword

class A{

}
A obj=new A();-- Valid

enum A{

}

A obj=new A();---ERROR