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:

Example

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:

Example

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

  public static void main(String[] args) {
    Level myVar = Level.MEDIUM;
    System.out.println(myVar);
  }
}

The output will be:

MEDIUM

Enum in a Switch Statement

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

Example

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;
    }
  }
}

The output will be:

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:

Example

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

The output will be:

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.