an API can return objects without making their classes public

[parthu_lkp]

How can we justify the below stmt

"an API can return objects without making their classes public"
(By using Static Factory methods)

If we justify the above stmt, can we access Objects in other packages also or those are valid in the same pack.?????

Could you please explain with example(without taking j2se/j2ee classes)???

thx
Parthu

[dlorde]

If the API returns an interface (as they generally should), then the caller doesn't need to know which class is implementing the interface. This means the class itself need not be public - it can even be a local anonymous class declared and instantiated inside the method being called; this is how iterators are provided by some collection classes. You don't have to use static factory methods, although they are useful for returning objects of different types depending on the context.

For example, the AbstractList class returns its iterators like this:

public Iterator<E> iterator() {
    return new Itr();
}

public ListIterator<E> listIterator() {
    return listIterator(0);
}

public ListIterator<E> listIterator(final int index) {
    if (index<0 || index>size())
        throw new IndexOutOfBoundsException("Index: "+index);

    return new ListItr(index);
}

The classes Itr and ListItr are private inner classes that implement the Iterator and ListIterator interfaces respectively.