Re: newInstance, generics, and "unchecked or unsafe operations"

From:

Stanimir Stamenkov <s7an10@netscape.net>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 15 Aug 2008 15:38:27 +0300

Message-ID:

<g83tc5$it3$1@registered.motzarella.org>

Fri, 15 Aug 2008 00:08:17 -0700, /Eric I./:

I'm trying to create a method in a class that takes some type of
genericized collection and creates a new, empty instance of it by
calling the newInstance method. I can get the code to work, but I do
get compiler warnings of "unchecked or unsafe operations".

[...]

class EmptyDuplicator<T>
{
    public Collection<T> duplicateEmptyVersionOf(Collection<T>
original)
           throws InstantiationException, IllegalAccessException
    {
        // COMPILER WARNING on next line; BUT I KNOW T at compile-
time!!!
        Collection<T> emptyVersionOf =
original.getClass().newInstance();
        return emptyVersionOf;
    }
}

Recently one has mentioned the Class.asSubclass [1] method but I
can't figure out which is the correct syntax, or if it is possible
at all:

         Class<? extends Collection<T>> c;
         // Syntax error in the |Collection<T>.class| part.
         c = original.getClass().asSubclass(Collection<T>.class);
         Collection<T> emptyVersionOf = c.newInstance();

[1]
http://java.sun.com/javase/6/docs/api/java/lang/Class.html#asSubclass(java.lang.Class)

--
Stanimir