Ivor Horton's Beginning Java™ 2, JDK™ 5th Edition

6.10. More on Enumerations

When I introduced enumerations in Chapter 2, I said that there was more to enumerations than simply a type with a limited range of integer values. In fact, an enumeration type is a special form of class. When you define an enumeration type in your code, the enumeration constants that you specify are created as instances of a class that has the Enum class, which is defined in the java.lang package, as a superclass. The object that corresponds to each enumeration constant stores the name of the constant in a field, and the enumeration class type inherits the toString method from the Enum class. The toString() method in the Enum class returns the original name of the enumeration constant, so that's why you get the name you gave to an enumeration constant displayed when you output it using the println() method.

You have seen that you can put the definition of an enumeration type within the definition of a class. You can also put the definition is a separate source file. In this case you specify the name of the file containing the enumeration type definition in the same way as for any other class type. An enumeration that you define in its own source file can be accessed by any other source file in exactly the same way as any other class definition.

An object representing an enumeration constant also stores an integer field. By default, each constant in an enumeration will be assigned an integer value that is different from all the other constants in the ...