Differences between Iterator & Enumeration:
Enumeration is twice as fast as Iterator and uses very less memory. Enumeration is very basic and fits to basic needs. But Iterator is much safer as compared to Enumeration, b’ coz it always denies other threads to modify the collection object which is being iterated by it. Whenever a second thread tries for that Iterator will throw a ConcurrentModificationException. Iterators that do this are known as fail-fast iterators, as they fail quickly and cleanly.

public interface Iterator

An iterator over a collection. Iterator takes the place of Enumeration in the Java collections framework. Iterators differ from enumerations in one way:

• Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics.

Method Summary

boolean hasNext() : Returns true if the iteration has more elements.

E next() : Returns the next element in the iteration.

void remove() : Removes from the underlying collection the last element returned by the iterator (optional operation).

An object that implements the Enumeration interface generates a series of elements, one at a time. Successive calls to the nextElement method return successive elements of the series.

For example, to print all elements of a vector v:

Methods are provided to enumerate through the elements of a vector, the keys of a hashtable, and the values in a hashtable. Enumerations are also used to specify the input streams to a SequenceInputStream.

Method Summary

boolean hasMoreElements() : Tests if this enumeration contains more elements.

E nextElement() : Returns the next element of this enumeration if this enumeration object has at least one more element to provide.