DIFFERENCE BETWEEN Enumeration and iterator?

[niisha guupta]

Can anyone explain me the difference between Enumeration and iterator?

[Christophe Verré]

Enumeration is an old twig from Java1.0. About the difference betweem Enumeration and Iterator, here is what the Enumeration API tells us :

API wrote:
The functionality of this interface is duplicated by the Iterator interface. In addition, Iterator adds an optional remove operation, and has shorter method names. New implementations should consider using Iterator in preference to Enumeration.

[Rob Spoor]

Like Christophe said, an Iterator can do the same an Enumeration can do, with added optional removal of elements. In fact, you can implement one backed by the other:

// given a final Iterator<? extends E> reference called iterator
new Enumeration<E>()
{
    public boolean hasMoreElements() { return iterator.hasNext(); }

    public E nextElement() { return iterator.next(); }
};

// given a final Enumeration<? extends E> reference called enumeration
new Iterator<E>()
{
    public boolean hasNext() { return enumeration.hasMoreElements(); }

    public E next() { return enumeration.nextElement(); }

    public void remove() { throw new UnsupportedOperationException(); }
};

Note that the remove() method throws an UnsupportedOperationException; this is done a lot when an interface defines an optional method and you wish not to really implement it. You must provide an implementation though because the interface still defines the method, so throwing this exception is the best implementation.