Enums in Java

Enums in Java are a special type of class that represent a group of constants (unchangeable variables). They were introduced in Java 5 and provide a type-safe way to define a fixed set of constants.

Basic Enum Syntax

public enum Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY
}

Key Features of Enums

1. Type Safety: You can't assign any value other than those predefined enum values.

2. Can Have Fields, Methods, and Constructors:
   

   public enum Planet {
       MERCURY(3.303e+23, 2.4397e6),
       VENUS(4.869e+24, 6.0518e6),
       EARTH(5.976e+24, 6.37814e6);

       private final double mass;   // in kilograms
       private final double radius; // in meters

       Planet(double mass, double radius) {
           this.mass = mass;
           this.radius = radius;
       }

       public double surfaceGravity() {
           return 6.67300E-11 * mass / (radius * radius);
       }
   }

1. Can Implement Interfaces:

   public interface Printable {
       void print();
   }

   public enum Color implements Printable {
       RED {
           public void print() {
               System.out.println("Red color");
           }
       },
       GREEN {
           public void print() {
               System.out.println("Green color");
           }
       };
   }

1. Can Be Used in Switch Statements:

   Day day = Day.MONDAY;

   switch(day) {
       case MONDAY:
           System.out.println("Start of work week");
           break;
       case FRIDAY:
           System.out.println("End of work week");
           break;
   }

Common Methods

• values(): Returns an array of all enum constants
• valueOf(String name): Returns the enum constant with the specified name
• ordinal(): Returns the position of the enum constant in the declaration (starting from 0)
• name(): Returns the name of the enum constant as a string

Example Usage

java
public class EnumExample {
    public static void main(String[] args) {
        // Accessing enum constants
        Day today = Day.WEDNESDAY;
        System.out.println("Today is " + today);

        // Using values() method
        for (Day day : Day.values()) {
            System.out.println(day);
        }

        // Using valueOf()
        Day day = Day.valueOf("FRIDAY");
        System.out.println("Day is " + day);
    }
}


Enums are particularly useful when you have a variable that should only take one of a small set of possible values, making your code more readable and less error-prone.