Hoinzey

Javascript. Kotlin. Android. Java

Enums

28th April 2021

An enum is a type whose values consist of a fixed set of constants. Before enums were introduced a common pattern used was declaring constants using named ints.


Kotlin
Java
named ints
                            
    enum class GameDifficulty {
        EASY,
        MEDIUM,
        HARD
    }
                        
                            
    enum GameDifficulty{
        EASY,
        MEDIUM,
        HARD
    }
                        
                            
    //Please stop doing this
    public static final int DIFFICULTY_EASY = 1;
    public static final int DIFFICULTY_MEDIUM = 2;
    public static final int DIFFICULTY_HARD = 3;

Enums allow you to add methods, fields and interfaces. An enum could potentially start out as a simple set of constants but end up becoming a full-featured abstraction.


Java - instance variables
Kotlin - switch on self
Java - abstract method
                            
    enum GameDifficulty{
        EASY(0.5),
        MEDIUM(1.0),
        HARD(2.0);
    
        public final double bossDifficultyModifier;
    
        GameDifficulty(double bossDifficultyModifier) {
            this.bossDifficultyModifier = bossDifficultyModifier;
        }
    }
                        
                            
    enum class GameDifficulty {
        EASY,
        MEDIUM,
        HARD;

        fun getBossDifficultyModifier(): Double {
            return when(this){
                EASY -> 0.5
                MEDIUM -> 1.0
                HARD -> 2.0
            }
        }
    }
                        
    
        enum GameDifficulty{
            EASY{
                public double getBossDifficultyModifier() {
                    return 0.5;
                }
            },
            MEDIUM{
                public double getBossDifficultyModifier() {
                    return 1.0;
                }
            },
            HARD{
                public double getBossDifficultyModifier() {
                    return 2.0;
                }
            };
        
            public abstract double getBossDifficultyModifier();
        }

EnumMaps


A special map which must take an Enum as its key. Internally it is represented as an array making it extremely fast and efficient 


                    
    List<PS4Game> gamesCollection = Arrays.asList(
        new PS4Game("Minecraft", GameDifficulty.EASY),
        new PS4Game("The Last of Us", GameDifficulty.MEDIUM),
        new PS4Game("Bloodborne", GameDifficulty.HARD));

    EnumMap<GameDifficulty, Set<PS4Game>> gamesByDifficulty = gamesCollection
        .stream()
        .collect(groupingBy(p -> p.gameDifficulty,
                () -> new EnumMap<>(GameDifficulty.class), toSet()));
    //{EASY=[Minecraft: EASY], 
    //MEDIUM=[The Last of Us: MEDIUM], 
    //HARD=[Bloodborne: HARD]}