newInstance, generics, and "unchecked or unsafe operations"

"Eric I." <>
Thu, 14 Aug 2008 21:05:00 -0700 (PDT)
Hi Everyone,

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".

Please note, I would like this code to be flexible, so whether the
method gets an ArrayList<Integer> or a LinkedList<String> it will work
and not generate compiler warnings.

In trying to hunt down a solution by reading
and other online sources, I became aware of the issue of "type
erasure". In fact, at compile time I should know the full type of the
collection. Is there a way to "nicely" re-write this code, so it
doesn't generate the warning? If not "nicely" how about "nastily"?


import java.util.Collection;
import java.util.ArrayList;

class EmptyDuplicator<T>
    public Collection<T> duplicateEmptyVersionOf(Collection<T>
           throws InstantiationException, IllegalAccessException
        // COMPILER WARNING on next line; BUT I KNOW T at compile-
        Collection<T> emptyVersionOf =
        return emptyVersionOf;

public class Sample
    public static void main(String[] args)
           throws InstantiationException, IllegalAccessException
        ArrayList<Integer> original = new ArrayList<Integer>();

        EmptyDuplicator<Integer> duplicator = new
        Collection<Integer> clone =

        for(int i : original) {

        for(int i : clone) {


Thanks in advance,


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