javaenumsstaticenum-map

What is the best way to statically initialize an EnumMap in Java


I need to statically initialize an EnumMap. I know two ways.

  1. Using of() method of Map

    private static final Map<<EnumKey>, <Value>> TEST_MAP = Map.of(ENUM_CONST1, "Value1", ENUM_CONST2, "Value2");
    
  2. Using double brace initialization

    private static final Map<<EnumKey>, <Value>> TEST_MAP = new EnumMap<>(EnumKey.class) {
        {
            put(ENUM_CONST1, "Value1");
            put(ENUM_CONST2, "Value2");
         }
    };
    

Is there any other cleaner and more efficient way?


Solution

  • A neat way to setup EnumMap is to define all the values in-line using Map.of or Map.ofEntries but note that this allocates a Map before the EnumMap constructor:

    private static final EnumMap<YourEnum,String> A = new EnumMap<>(Map.of(
            YourEnum.ONE, "Value1",
            YourEnum.TWO, "Value2"
    ));
    
    // Use Map.ofEntries for enums with more than 10 values:
    private static final EnumMap<YourEnum,String> B = new EnumMap<>(Map.ofEntries(
            Map.entry(YourEnum.ONE, "Value1"),
            Map.entry(YourEnum.TWO, "Value2")
    ));
    

    If wanting public access then wrap as unmodifiable Map (which is backed by EnumMap) or just pass back Map.of directly (but is not using an EnumMap).

    public static final Map<YourEnum,String> C = Collections.unmodifiableMap(B);