Re: Generics, factories and reflection

From:

Thomas Hawtin <usenet@tackline.plus.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 19 Sep 2006 13:12:39 +0100

Message-ID:

<450fde82$0$574$ed2619ec@ptn-nntp-reader03.plus.net>

Martin wrote:
> public static List<E> createList() {
public static <E> List<E> createList() {

You need to declare the generic parameter.

But in my special case, I want to (and have to) pass the implementing
class as an argument. So the factory could create instances of
ArrayList but also of LinkedList. The following method compiles without
warnings and errors:

--------------------------------------------------------------
public static List<E> createList(Class<? extends List<E>> listImpl) {
    try {
        List<E> l = listImpl.newInstance();
        return l;

I strongly suggest you don't use Class.newInstance. That method is evil.
Much better to write an abstract factory interface. Also, important for
this use, Class represents an erased type. In any case, creating a
LinkedList is likely to be a bad idea.

    }
    catch (Exception dontBotherMe) {
        return null;
    }
}

Nice error handling...

Tom Hawtin
--
Unemployed English Java programmer
http://jroller.com/page/tackline/