The compiler may choose foreach loop implementation
with respect to declared collection type.

I proposed the following rule :
if collection is a List that implements RandomAccess,
use indexed loop rather than iterator loop
else use Iterable interface.

In order to convince you, this paragraph is extracted from
RandomAccess documentation :

A List implementation should implement this interface if, for typical
instances of the class, this loop:

       for (int i=0, n=list.size(); i < n; i++)
           list.get(i);


runs faster than this loop:

       for (Iterator i=list.iterator(); i.hasNext(); )
           i.next();