Re: Interface inheritance vs Implementation inheritance.
Patricia Shanahan <pats@acm.org> writes:
To make this a bit more specific, consider ArrayList. It implements a
series of interfaces. Those describe the general behavior its callers
can depend on: it's a list, it has fast random access, it can be cloned
and serialized, and it has an Iterator.
In addition, it extends AbstractList. That seems to me to be part of its
implementation, and not something I would use in my code. And yet, a
class outside java.util could declare:
AbstractList<String> someList = new ArrayList<String>();
It might be advantageous to split AbstractList, for example to provide
different implementations depending on whether the list has fast random
access. That cannot be done, because of the public nature of the uses of
AbstractList.
Agreed.
I wouldn't mind a language where implementation inheritance wasn't public,
i.e., your type only consists of interfaces. If you extend another class,
you also implements its interfaces, but the extended class is not part
of your type.
And I would also like an easy way to create a composition, e.g.,
class Foo implements Bar(b) {
private Bar barbarbar implements Bar; // or delegates Bar
public Foo(int i) {
super(i);
this.barbarbar = new Bar(i);
}
//...
}
/L
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