How to store enum to map using Java 8 stream API

Question

I have an enum with another enum as a parameter

public enum MyEntity{
   Entity1(EntityType.type1,
    ....


   MyEntity(EntityType ty         


        

Answer 1

I guess there are some typos in your code (the method should be static in my opinion, your constructor is doing a no-op at the moment), but if I'm following you, you can create a stream from the array of enums and use the toMap collector, mapping each enum with its EntityType for the keys, and mapping the instance itself as a value:

private static final Map lookup =
    Arrays.stream(EntityTypeInfo.values())
          .collect(Collectors.toMap(EntityTypeInfo::getEntityType, e -> e));

The toMap collector does not make any guarantee about the map implementation returned (although it's currently a HashMap), but you can always use the overloaded variant if you need more control, providing a throwing merger as parameter.

You could also use another trick with a static class, and fill the map in the constructor.