Java Enums

Enums

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

To create an enum, use the enum keyword (instead of class or interface), and separate the constants with a comma. Note that they should be in uppercase letters:

enum Level {
  LOW,
  MEDIUM,
  HIGH
}

You can access enum constants with the dot syntax:

Level myVar = Level.MEDIUM;

Enum is short for "enumerations", which means "specifically listed".

Enum inside a Class

You can also have an enum inside a class:

public class Main {
  enum Level {
    LOW,
    MEDIUM,
    HIGH
  }
 
  public static void main(String[] args) {
    Level myVar = Level.MEDIUM; 
    System.out.println(myVar);
  }
}

Output:

MEDIUM

Enum in a Switch Statement

Enums are often used in switch statements to check for corresponding values:

enum Level {
  LOW,
  MEDIUM,
  HIGH
}
 
public class Main {
  public static void main(String[] args) {
    Level myVar = Level.MEDIUM;
 
    switch(myVar) {
      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:

Medium level

Loop Through an Enum

The enum type has a values() method, which returns an array of all enum constants. This method is useful when you want to loop through the constants of an enum:

for (Level myVar : Level.values()) {
  System.out.println(myVar);
}

Output:

LOW
MEDIUM
HIGH

Difference between Enums and Classes

An enum can, just like a class, have attributes and methods. The only difference is that enum constants are public, static, and final (unchangeable - cannot be overridden).

An enum cannot be used to create objects, and it cannot extend other classes (but it can implement interfaces).

Why And When To Use Enums?

Use enums when you have values that you know aren't going to change, like month days, days, colors, deck of cards, etc.