Java Reference
In-Depth Information
Because
meth( )
is declared as
final
, it cannot be overridden in
B
. If you attempt to do so,
a compile-time error will result.
final Prevents Inheritance
You can prevent a class from being inherited by preceding its declaration with
final
. De-
claring a class as
final
implicitly declares all of its methods as
final
, too. As you might
expect, it is illegal to declare a class as both
abstract
and
final
since an abstract class is
incomplete by itself and relies upon its subclasses to provide complete implementations.
Here is an example of a
final
class:
As the comments imply, it is illegal for
B
to inherit
A
since
A
is declared as
final
.
Using final with Data Members
In addition to the uses of
final
just shown,
final
can also be applied to member variables to
create what amounts to named constants. If you precede a class variable's name with
final
,
its value cannot be changed throughout the lifetime of your program. You can, of course,
give that variable an initial value. For example, in
Chapter 6
a simple error-management
class called
ErrorMsg
was shown. That class mapped a human-readable string to an error
code. Here, that original class is improved by the addition of
final
constants which stand
for the errors. Now, instead of passing
getErrorMsg( )
a number such as 2, you can pass
the named integer constant
DISKERR
.
