Java Reference
In-Depth Information
The identifiers
CAR
,
TRUCK
, and so on, are called
enumeration constants
. Each is im-
plicitly declared as a public, static member of
Transport
. Furthermore, the enumeration
constants' type is the type of the enumeration in which the constants are declared, which is
Transport
in this case. Thus, in the language of Java, these constants are called
self-typed
,
where “self” refers to the enclosing enumeration.
Once you have defined an enumeration, you can create a variable of that type. However,
even though enumerations define a class type, you do not instantiate an
enum
using
new
.
Instead, you declare and use an enumeration variable in much the same way that you do
one of the primitive types. For example, this declares
tp
as a variable of enumeration type
Transport
:
Because
tp
is of type
Transport
, the only values that it can be assigned are those defined
by the enumeration. For example, this assigns
tp
the value
AIRPLANE
:
Notice that the symbol
AIRPLANE
is qualified by
Transport
.
Two enumeration constants can be compared for equality by using the
= =
relational op-
erator. For example, this statement compares the value in
tp
with the
TRAIN
constant:
An enumeration value can also be used to control a
switch
statement. Of course, all of
the
case
statements must use constants from the same
enum
as that used by the
switch
ex-
pression. For example, this
switch
is perfectly valid:
