Iterator Interface. A question?

Question

I am unable to grasp the meaning of the following below :
As we all know,Interfaces have abstract methods,(ie methods that
have no body) and any class that implements the Interface has to
implement the methods defined in the interface.That is,write the body for those methods.
So far so good.
Now coming to Collections called Vector.
We have the 'Iterator' interface implemented by the vector class.
The Iterator interface has the methods hasNext(),next().
and we have the following code in the our class which iterates thru'
the vector:
MyClass item;
while(iter.hasNext())
item = (MyClass)iter.next();
// Do something here.....
We are using the methods hasNext() and next() above.
But as they belong to the Iterator interface,(which means they
are basically methods with no implementations) then how is iteration
possible? We havent defined anything in the hasNext() method or the next()
so how does Java automatically start iteration
Has any one understood my question?Arent hasNext() and next() supposed
to be methods with no body?.
Arent they supposed to be empty()?
If they have no body,then how are they being implemented?
If I am saying iter.hasNext(),that means hasNext() has been defined
somewhere to iterate thru the vector?
I am just confused regarding this issue as to how is hasNext() and next()
being implemented as I as the programmer have not implemented them
in my code
Please can some one answer my question?
Regards
Ajay

Answer 1

public Iterator iterator()
Returns an iterator over the elements in this list in proper sequence.
This implementation returns a straightforward implementation of the iterator interface, relying on the backing list's size(), get(int), and remove(int) methods.
Note that the iterator returned by this method will throw an UnsupportedOperationException in response to its remove method unless the list's remove(int) method is overridden.
This implementation can be made to throw runtime exceptions in the face of concurrent modification, as described in the specification for the (protected) modCount field.
Specified by:
iterator in interface List
Specified by:
iterator in class AbstractCollection
Returns:
an iterator over the elements in this list in proper sequence.
See Also:
modCount
So based on the above JavaDoc for java.util.AbstractList, which Vector sub-classes, the iterator() method returns an implementaion of the iterator interface. This is where the methods are defined.