Question

Iterable<E> is in java.lang whereas Iterator<E> is in java.util. Is there a good reason for this or is this merely an artifact of bad design?

It seems strange since the only thing that an Iterable<E> is good for is providing an Iterator<E>.

EDIT: One potential reason is because of the (then-)newly introduced for-each loop. I guess my question then would be, are they equivalent?

for(Object o : collection)
    ...
vs
for( Iterator iter = collection.iterator(); iter.hasNext(); ) {
    o = iter.next();
    ...

If they are, then that still doesn’t explain why the two classes are in different packages since the compiler would have to import java.util anyways to use the Iterator construct.

Answer 1

Part of it is history: Iterator has been with us since JDK 1.2, and Iterable came with JDK 1.5. Iterable came in with the enhanced for loop.

Bad design? No, evolution. There’s no all-knowing creator. As lessons are learned they’re incorporated into the JDK.