Force Initialization of an enumerated type in Java

Question

I am attempting to find a way to force Java to load/initialize an enumerated type (which is nested within a class that contains a static Map).

This is important to me because the enumerated type has a constructor that populates said map, and without an explicit way to initialize this enum, the map will remain empty. I have attempted to use Class.forName, but this does not seem to work.

I suppose I could create an instance of the enum (and store it in soem other collection or something), but I would like to know if there is an elegant way to do this.

Answer 1

A class is loaded when you reference a class. This works the same for all classes.

The problem you have is more likely to be that an Enum value is initialised before any static block. i.e. you cannot refer to something initialise in a static block in a constructor. (Generally initialising static content in a constructor is a BAD idea) You need to initialise the Map in the static block, not the constructor.

Try

import java.util.Map; 
import java.util.HashMap; 

public enum EnumTest { 
  FOO, BAR, BAZ; 

  private static final Map<String,EnumTest> map = new LinkedHashMap<String,EnumTest>(); 
  static { 
      for(EnumTest e : EnumTest.values())
        map.put(e.name(), e); 
  } 

  public static void main(String... args) { 
    System.out.println(EnumTest.map); 
  } 
}

Answer 2

Can't you just put initialization of the map in the static initializer of the Enum type?

public enum SomeEnum
{
    Member1, Member2, Member3 ...

    private static Map<K, SomeEnum> map = ...;
    static 
    {
        ...populate map...
    }
    ...

EDIT: It appears that the issue was that the Enum member definitions need to come first. I guess I just glossed over this. I fixed the example.