Java Reference
In-Depth Information
* name.
* The string must match exactly an identifier used to declare
* an enum constant in this type. (Extraneous whitespace
* characters are not permitted.)
*
* @return the enum constant with the specified name
* @throws IllegalArgumentException if this enum type has no
* constant with the specified name
*/
public static E valueOf(String name);
It follows that enum type declarations cannot contain fields that conflict with the
enum constants, and cannot contain methods that conflict with the automatically gen-
erated methods (
values()
and
valueOf(String)
) or methods that override the
final
methods
in Enum (
equals(Object)
,
hashCode()
,
clone()
,
compareTo(Object)
,
name()
,
ordinal()
, and
getDe-
claringClass()
).
It is a compile-time error to reference a
static
field of an enum type that is not a constant
variable (§
4.12.4
) from constructors, instance initializer blocks, or instance variable initial-
izer expressions of that type.
It is a compile-time error for the constructors, instance initializer blocks, or instance vari-
able initializer expressions of an enum constant
e
to refer to
e
or to an enum constant of the
same type that is declared to the right of
e
.
Example 8.9.2-1. Restriction On Enum Constant Self-Reference
Without this rule, apparently reasonable code would fail at run time due to the ini-
tialization circularity inherent in enum types. (A circularity exists in any class with a
“self-typed”
static
field.) Here is an example of the sort of code that would fail:
import java.util.Map;
import java.util.HashMap;
enum Color {
RED, GREEN, BLUE;
static final Map<String,Color> colorMap =
new HashMap<String,Color>();
Color() { colorMap.put(toString(), this); }
}
