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Java Enum Class

 

In Java, when you need a fixed set of constants—like days of the week, directions (NORTH, SOUTH, EAST, WEST), or traffic light signals—using integers or strings can be error-prone.

To solve this, Java provides the enum (enumeration) class, which is a special data type that represents a group of predefined constants.

In this guide, we’ll cover:

  • What enums are
  • Defining enums
  • Adding fields, constructors, and methods
  • Using enums in switch statements
  • Examples with code

What Is an Enum in Java?

 
  • An enum is a special Java class that represents a group of constants.
  • Enums are type-safe, meaning you can’t assign invalid values.
  • Internally, each enum constant is an object of the enum type.

Example: Basic Enum

 

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

public class EnumExample {
  public static void main(String[] args) {
    Day today = Day.MONDAY;
    System.out.println(“Today is ” + today);
  }
}

Output:

Today is MONDAY

Enum with Switch Statement

 

Enums work seamlessly with switch statements.

public class SwitchEnumExample {
  enum Level { LOW, MEDIUM, HIGH }

  public static void main(String[] args) {
    Level level = Level.HIGH;

    switch (level) {
      case LOW:
        System.out.println(“Low level”);
        break;
      case MEDIUM:
        System.out.println(“Medium level”);
        break;
      case HIGH:
        System.out.println(“High level”);
        break;
    }
  }
}

Output:

High level

Enum with Fields, Constructors, and Methods

 

Enums can have:

  • Fields (attributes)
  • Constructors (always private)
  • Methods (custom behavior)

Example: Traffic Light Enum

 

public enum TrafficLight {
  RED(30), YELLOW(5), GREEN(25);

  private int duration; // field

  // constructor
  TrafficLight(int duration) {
    this.duration = duration;
  }

  // method
  public int getDuration() {
    return duration;
  }
}

public class TrafficLightExample {
  public static void main(String[] args) {
    for (TrafficLight light : TrafficLight.values()) {
      System.out.println(light + ” lasts ” + light.getDuration() + ” seconds.”);
    }
  }
}

Output:

RED lasts 30 seconds.
YELLOW lasts 5 seconds.
GREEN lasts 25 seconds.

Enum Methods

 
  • values() → returns an array of all enum constants.
  • valueOf(String name) → returns the enum constant with the given name.
  • ordinal() → returns the position of the constant (0-based).

Example:

 

public class EnumMethodsExample {
  enum Direction { NORTH, SOUTH, EAST, WEST }

  public static void main(String[] args) {
    for (Direction d : Direction.values()) {
      System.out.println(d + ” at index ” + d.ordinal());
    }

    Direction dir = Direction.valueOf(“EAST”);
    System.out.println(“Chosen direction: ” + dir);
  }
}

Advantages of Enums

 
  • Type-safe alternative to integers or strings.
  • Can include fields, methods, and constructors.
  • Easy to use in switch statements.
  • Prevents invalid constant values.

Best Practices

 
  • Use enums for fixed sets of constants.
  • Add fields and methods when constants need associated values.
  • Use switch with enums for cleaner conditional logic.
  • Prefer enums over integer/string constants for readability and safety.

Conclusion

 

Java enum classes provide a powerful way to define constant groups in a type-safe manner.

  • Use enums for fixed categories like days, levels, and directions.
  • Enhance enums with fields, methods, and constructors for more flexibility.
  • Use enums in switch statements for clean logic.

By mastering enums, you’ll make your Java code more readable, maintainable, and error-free.

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