Why is remove forbidden in for/in?

Question

Java

All sources simply indicate this limitation, but the reason is not indicated, and for me it is not obvious. Requires explicit use of Iterator. Why can't you do this:

public void remove(Set<Cat> cats) {
for (Cat cat : cats) 
    cats.remove(cat);
}

Answer 1

Because you're cutting the branch you're sitting on.

List<String> names = ....
Iterator<String> i = names.iterator();
while (i.hasNext()) {
   String s = i.next(); // must be called before you can call i.remove()
   // Do something
   i.remove();
}