What is Iterator Interface In Java ?

Previously we have discussed about

What is Map.Entry In Java ?

Here we learn about Iterator Interface in Java, but before that we must know What is Collection Interface in Java ?

Interface Iterator<E>

Type Parameters:

E - the type of elements returned by this iterator

All Known Subinterfaces:

ListIterator<E>, XMLEventReader

All Known Implementing Classes:

BeanContextSupport.BCSIterator, EventReaderDelegate, Scanner

Declaration of Iterator:

public interface Iterator<E>

Each of the collection classes provides an iterator( ) method that returns an iterator to the start of the collection.By using this iterator object, you can access each element of the collection but one element at a time.

Iterator takes the place of Enumeration in the Java Collections Framework. Iterators differ from enumerations in two ways:

1) Iterators allows to remove elements from collection during the iteration.

2) Iterators have well improved method names.

To use an iterator to access the elements of a collection, follow these steps:

1) First call the collection Iterator() method.

2) Set up a loop that makes a call to hasNext() method, as long as this method returns true.

3) Now, with in the loop get each element by calling the next() method.

This interface is a member of the Java Collections Framework.

Method Summary of Iterator:

Modifier and Method Name	Description
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 this iterator (optional operation).

Example of Iterator:

import java.util.ArrayList;

import java.util.Iterator;

public class IteratorInterfaceExample {

public static void main(String[] args) {

ArrayList<String> al = new ArrayList<String>();

// Add elements to the array list.

al.add("C");

al.add("A");

al.add("E");

al.add("B");

al.add("D");

al.add("F");

// Use iterator to display contents of ArrayList 

System.out.println("Elements of ArrayList : ");

Iterator<String> itr = al.iterator();

while(itr.hasNext()) {

String element = itr.next();

System.out.println(element);

}

//Remove method removes all the elements from Iterator

itr.remove();

System.out.println("No Elements Found After Iterator Remove method : ");

while(itr.hasNext()) {

String element = itr.next();

System.out.println(element);

}

}

}

Program Output:

Elements of ArrayList : 

C

A

E

B

D

F

No Elements Found After Iterator Remove method : 

      

Blog Author - Pushkar Khosla,
Software Developer by Profession with 3.0 Yrs of Experience , through this blog i'am sharing my industrial Java Knowledge to entire world. For any question or query any one can comment below or mail me at pushkar.itsitm52@gmail.com.

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