Enumerations or Java Enum serve the purpose of representing a group of named constants in a programming language.

To create an enum, use the enum keyword

Declaration of enum in Java
Enum declaration can be done outside a class or inside a class but not inside a method.[TBD]

  1. Declaration outside the class 
// A simple enum example where enum is declared
// outside any class (Note enum keyword instead of
// class keyword)
enum Color {
    RED,
    GREEN,
    BLUE;
}

public class Test {
    // Driver method
    public static void main(String[] args) {
        Color c1 = Color.RED;
        System.out.println(c1);
    }
}

2. Declaration inside a class

// enum declaration inside a class.
public class Test {
    enum Color {
        RED,
        GREEN,
        BLUE;
    }

    // Driver method
    public static void main(String[] args) {
        Color c1 = Color.RED;
        System.out.println(c1);
    }
}

3. Enum in a Switch Statement

Enums can be used in switch statements to handle different cases based on the enum constants.

// Java Program to implement
// Enum in a Switch Statement
import java.io.*;

// Driver Class
class GFG {
    // Enum Declared
    enum Color {
        RED,
        GREEN,
        BLUE,
        YELLOW;
    }

    // Main Function
    public static void main(String[] args) {
        Color var_1 = Color.YELLOW;

        // Switch case with Enum
        switch (var_1) {
        case RED:
            System.out.println("Red color observed");
            break;
        case GREEN:
            System.out.println("Green color observed");
            break;
        case BLUE:
            System.out.println("Blue color observed");
            break;
        default:
            System.out.println("Other color observed");
        }
    }
}

Reference link :
https://www.geeksforgeeks.org/enum-in-java/