Overriding same method twice from same class

Question

I was understanding how iterator() method works with ArrayList class . In ArrayList class I found iterator() method overridden twice from same class AbstractList .

public Iterator<E> iterator() {
    return new Itr();         // Itr is an inner private class of 
                               //   ArrayList which 
                              // implements Iterator interface .
}

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

But how is this possible ? There should be an error here of already defined . I am confused .

Answer 1

The first iterator() method you see belongs to the ArrayList class, but the second does not.

It belongs to the SubList class, which is an inner class of ArrayList :

private class SubList extends AbstractList<E> implements RandomAccess {
    ...
    public Iterator<E> iterator() {
        return listIterator();
    }
    ...
}

Therefore it is not overridden twice by the same class. Each class overrides it once.

Answer 2

Overriding the same method twice from same class is not allowed. In your case, these are two different classes, namely:

public class ArrayList<E> extends AbstractList<E>
private class SubList extends AbstractList<E> implements RandomAccess 

and the latter is an inner class of the former, that's why both can have same method with same signature.