Re: Destructively merging two LinkedLists

From:
Eric Sosman <esosman@ieee-dot-org.invalid>
Newsgroups:
comp.lang.java.programmer
Date:
Mon, 10 Jan 2011 09:55:16 -0500
Message-ID:
<igf6lq$nfi$1@news.eternal-september.org>
On 1/10/2011 9:26 AM, Joshua Cranmer wrote:

On 01/10/2011 09:14 AM, Eric Sosman wrote:

class RaphfrkList<T> extends AbstractSequentialList<T> {
boolean stealAll(RaphfrkList<? extends T> from) {
// O(1) magic here ...
}
boolean stealAll(Collection<? extends T> from) {

if (from instanceof RaphfrkList)
return stealAll((RaphfrkList)from);

boolean result = addAll(from);
from.clear();
return result;
}
// ...
}


Java does not do dynamic dispatch based on real types of arguments.


     True, if he uses a List (or Queue or Collection or ...) reference
to point to a RaphfrkList object, he'll get the vanilla stealAll().
but if he uses a RaphfrkList reference

    RaphfrkList listA = new RaphfrkList();
    RaphfrkList listB = new RaphfrkList();
    // ...
    listA.stealAll(listB);

.... then he'll get the specialized version. (The usual advice to use
interface references in preference to implementation references can
be disregarded, I think, in cases where an implementation-specific
functionality is desired.)

     Alternatively, he could decorate the vanilla method:

    boolean stealAll(Collection<? extends T> from) {
        if (from instanceof RaphfrkList)
            return stealAll( (RaphfrkList<? extends T>)from );
        //...
    }

(Double-check the cast; I'm not at all sure I wrote it correctly.)

--
Eric Sosman
esosman@ieee-dot-org.invalid

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