Iterator interface in java and its use.

Iterator interface in java is a part of collection framework in java.util package.It is used to iterate through a collection Ex : HashMap , HashSet etc.

There are three types iterators :

• Enumeration ~

this interface is for legacy collection(Vector, Hashtable) .it goes only in forward direction.

//e is an object of Enumeration type interface
//vec is a vector class object
Enumeration e = vec.elements();

• iterator ~

this is an universal iterator which can be used for any collection object.It is only forward directional.

//instantiating iterator object
Iterator itrerator_object = collection_object.iterator()

it has followinf functions:

// Returns true if the iteration(vales in a collection) has more elements
// public boolean hasNext();
//public Object next();
//public void remove();
while(iterator_object.hasNext())
{
int x = iterator_object.next();
System.out.println(x);
//removing the next element from the  iteration
iterator_object.remove();
}

• ListIterator ~

this only applicable for list collection and is bidirectional.

// ListIterator_object is of type ListIterator interface
ListIterator ListIterator_object = list_object.listIterator();

it has more functions than iterator:

// Forward direction

//public boolean hasNext(); 
//public Object next();
//public int nextIndex();

// Backward direction

//public boolean hasPrevious();
//public Object previous();
//public int previousIndex();

// Other Methods
 

//public void remove();

// Replaces at current position 
public void set(Object obj);

// Inserts at current position 
public void add(Object obj);