Java, A Beginner's Guide, 5th Edition, 5th Edition

Enumerations Inherit Enum

Although you can’t inherit a superclass when declaring an enum, all enumerations automatically inherit one: java.lang.Enum. This class defines several methods that are available for use by all enumerations. Most often you won’t need to use these methods, but there are two that you may occasionally employ: ordinal( ) and compareTo( ).

The ordinal( ) method obtains a value that indicates an enumeration constant’s position in the list of constants. This is called its ordinal value. The ordinal( ) method is shown here:

final int ordinal( )

It returns the ordinal value of the invoking constant. Ordinal values begin at zero. Thus, in the Transport enumeration, CAR has an ordinal value of zero, TRUCK has an ordinal value of ...