Re: Generics in Java 1.5 ( or is it java 5.0 ?... I always have
confusion)
Vikram wrote:
Hi,
Looking at the signature of the following method in
java.util.List
public interface List<E> extends Collection<E> {
.........
........
......
<T> T[] toArray(T[] a);
}
I wrote a small program as below:
ArrayList<String> c = new ArrayList<String>();
c.add("Vikram");
c.add("Pyati");
Integer[] i = new Integer[20];
c.toArray(i);
This did not give me a compilation error, though it fails at runtime
giving java.lang.ArrayStoreException, which is perfect.
My question is , why did the above mentioned method be declared as
<E> E[] toArray(E[] a);
which will force the method to take only the array of formal type ( in
this case a String[] ) at the compile time
So, first off, Generics and Arrays don't always mix well.
Second, I think you're attempting to express this:
<T super E> toArray(T[] a);
Although, that breaks this:
List<Number> c = new ArrayList<Number>();
c.add(new Integer(3));
c.add(new Integer(15));
Integer[] i = c.toArray(new Integer[0]);
the toArray(Object[]) method is inherently a run-time only method,
because it can be used to create any type of array.
--
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