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 Type Safety: You can't assign any value other than those predefined enum values. 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); } } 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"); } }; } 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.

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

   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);
       }
   }

   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");
           }
       };
   }