Java Reference
In-Depth Information
Suppose we had a custom list implementation called
MyCustomList
and had implemented a
custom
addAll
method, and the new
List
interface provided a
default addAll
that deleg-
ated to the
add
method. If the
default
method wasn't guaranteed to be overridden by this
addAll
method, we could break the existing implementation.
Multiple Inheritance
Because interfaces are subject to multiple inheritance, it's possible to get into situations
where two interfaces both provide
default
methods with the same signature. Here's an ex-
ample in which both a
Carriage
and a
Jukebox
provide a method to
rock
—in each case, for
different purposes. We also have a
MusicalCarriage
, which is both a
Jukebox
Example 4-19. Jukebox
public
public interface
interface
Jukebox
Jukebox
{
public
public default
default
String
rock
() {
return
return
"... all over the world!"
;
}
}
Example 4-20. Carriage
public
public interface
interface
Carriage
Carriage
{
public
public default
default
String
rock
() {
return
return
"... from side to side"
;
}
}
public
public class
class
MusicalCarriage
MusicalCarriage
implements
implements
Carriage
,
Jukebox
{
}
Because it's not clear to
javac
which method it should inherit, this will just result in the
compile error
class MusicalCarriage inherits unrelated defaults for rock()
from types Carriage and Jukebox
. Of course, it's possible to resolve this by implement-
