Enumeration Types - The Java Programming Language - page 231

6.4. java.lang.Enum
All enum types implicitly extend java.lang.Enum , [3] but no class is allowed
to extend Enum directly. Although Enum does provide some methods that
can be useful for working with enums, its main role is to establish some
useful properties for all enum types:
[3] Enum is actually a generic class defined as Enum<T extends Enum<T>>. This circular definition is prob-
ably the most confounding generic type definition you are likely to encounter. We're assured by the type
theorists that this is quite valid and significant, and that we should simply not think about it too much, for
which we are grateful.
• The clone method is overridden to be declared final and to throw
CloneNotSupportedException making it impossible to ever clone an
enum instance.
• The hashCode and equals methods are overridden and declared fi-
nal ensuring consistent and efficient hashing for enums, and ensur-
ing that equivalence is the same as identity.
• The compareTo method of interface java.lang.Comparable is imple-
mented and defined such that enum constants have a natural or-
dering based on their order of declarationthe first declared enum
constant has the lowest position in the ordering.
Enum also provides a toString implementation that returns the name of
the enum constant, as we have mentioned, but which you can chose to
override. It also provides a finalname method that also returns the name
of the enum constant as a String . The difference between these two
methods is that name will return the exact name of the enum constant,
while toString may be overridden to return a more "user friendly" version
of the namefor example, returning "Diamonds" instead of "DIAMONDS" .
The additional methods of Enum are:
public final int ordinal()