Question

Enumeration interface has method hashMoreElements is used with refrence variable (Enumv), how can they be used
since they are not implemented ?
I meant it is an interface method so how can it be called – Enumv.hasMoreElements() it does not have a implementation .

Vector v = new Vector();
//v contains list of elements - Suppose
Enumeration Enumv = v.elements();
while(Enumv.hasMoreElements()) {
    System.out.println(Enumv.nextElement());
}

How is this possible?

Answer 1

For your code,

Enumeration Enumv = v.elements();

This is what Vector is returning to you.

public Enumeration<E> elements() {
    return new Enumeration<E>() {
        int count = 0;

        public boolean hasMoreElements() {
        return count < elementCount;
        }

        public E nextElement() {
        synchronized (Vector.this) {
            if (count < elementCount) {
            return (E)elementData[count++];
            }
        }
        throw new NoSuchElementException("Vector Enumeration");
        }
    };
}

As you can see, Vector returns an implemented Enumeration class (which annonymous to the developer).

so how can it be called – Enumv.hasMoreElements() it does not
have a implementation .

It is implemented (as shown above).