“Iterable cannot be cast to List” - Isn't `List` a type of `Iterable`?

Question

I called a getElements method which returns Iterable.

I did this:

List elements = (List

        

Answer 1

You can turn Iterable into a List with

List<Element> elements = Lists.newArrayList( getElements() );

Answer 2

List extends Collection which in turn extends Iterable. You therefore trying to cast to a subtype which won't work unless getElements() really is returning a List (which the signature doesn't in any way guarantee).

See: http://download.oracle.com/javase/1.5.0/docs/api/java/util/List.html

Answer 3

Not all Iterables are Lists, thus it's not safe to cast an arbitrary Iterable to a List.

Take any Set for instance, a HashSet is Iterable but the elements has no order, so it can't implement the List interface, and is thus not a List.

Answer 4

why not:

    Iterable<Element> i = ...; //is what you have
    List<Element> myList = new LinkedList<Element>();
    for (Element e:i) {
        myList.add(e);
    }

? needs no google lib.

Answer 5

List<Element> is a type of Iterable<Element>, but that doesn't mean that all Iterable<Element> objects are List<Element> objects. You can cast a List<Element> as an Iterable<Element>, but not the other way around.

An apple is a type of fruit, but that doesn't mean that all fruits are apples. You can cast an apple as a fruit, but not the other way around.

Answer 6

From exception message it is clear that Iterable<Element> is not castable to List<Element>

SO you need to return List<Element> from getElements()