Dynamic Enums in Java

The Enum was introduced in Java 1.5. By definition its members are static and no members can be added at run time. Sometimes it is very convenient to store the items or to store additional items in a DB or on file. This is where the dynamic enum (DEnum) comes into play.

The DEnum class has a signature similar to the standard Enum class:

public abstract class DEnum<E extends DEnum<E>> implements Comparable<E>, Serializable {

 It has a protected constructor to allow instance creation in concrete Enum classes. For example:

public class YesNo extends DEnum<YesNo> {

	  public final static YesNo YES = new YesNo();
 	  public final static YesNo NO = new YesNo();

The DEnum class knows the names of the members by introspection:

    // when not set the name is lazily computed by introspection
	protected String name = null;

	public String getName() {
		if (name == null) {
			Class<?> clazz = getClass();
			// Scan the static enumeration values defined in the enumeration
			// class to compute name
			Field[] fields = clazz.getDeclaredFields();
			for (Field field : fields) {
				try {
					Object object = field.get(this);
					if (this == object) {
						name = field.getName();
						break;
					}
				} catch (IllegalArgumentException ex) {
					logger.log(Level.SEVERE, ex.getMessage(), ex);
				} catch (IllegalAccessException ex) {
					// normal behaviour, this property is private, so skip it
					logger.fine("field " + field.getName() + " is private : " + ex.getMessage());
				}
			}

			if (name == null) {
				throw new IllegalArgumentException("Can't find name for enum");
			}
		}
		return name;
	}

Usage is as follows:

String name = YesNo.YES.getName();
YesNo yes = YesNo.get(YesNo.class, name);
assert (yes == YesNo.YES);

  There is a typed getter that retrieves all the items:

YesNo[] items = yes.getItems();
assert (items.length == 2);

It allows to add members dynamically at run time with (from database or from file):

YesNo maybe = getOrCreateIfNotExists(YesNo.class, "MAYBE");
items = yes.getItems();
assert (items.length == 3);

Which have the same behavior as the static members: 

YesNo unknown = YesNo.get(YesNo.class, "MAYBE");
assert (unknown == maybe);