Java Iterator

Iterator In Java

Often, you will want to cycle through the elements in a collection.
For example, you might want to display each element.
One way to do this is to employ an iterator.
Before you can access a collection through an iterator,you must have one
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 in the collection, one element at a time.
In general, to use an iterator to cycle through the contents of a collection, follow these steps -

Obtain an iterator to the start of the collection by calling the collection’s iterator( ) method.
Set up a loop that makes a call to hasNext( ). Have the loop iterate as long as hasNext( ) returns true.
Within the loop, obtain each element by calling next( ).

Following are the methods used to iterate in Collections in Java -

Example -

package javaLearnings;

import java.util.*;

// Web desining House

// Online Promotion House
// Demonstrate Iterator -.
public class Main {

public static void main(String args[]) {
// Create an array list.
ArrayList<String> al = new ArrayList<String>();
// Add elements to the array list.
al.add("W");
al.add("E");
al.add("B");
al.add("S");
al.add("I");
al.add("T");
al.add("E");
// Use iterator to display contents of al.
System.out.print("Original contents of al: ");
Iterator<String> itr = al.iterator();
while(itr.hasNext()) {
String element = itr.next();
System.out.print(element + " ");
}
System.out.println();
// Modify objects being iterated.
ListIterator<String> litr = al.listIterator();
while(litr.hasNext()) {
String element = litr.next();
litr.set(element + "+");
}
System.out.print("Modified contents of al: ");
itr = al.iterator();
while(itr.hasNext()) {
String element = itr.next();
System.out.print(element + " ");
}
System.out.println();
// Now, display the list backwards.
System.out.print("Modified list backwards: ");
while(litr.hasPrevious()) {
String element = litr.previous();
System.out.print(element + " ");
}
System.out.println();
}
}

Output -

We can also use FOR-each loop instead of iterator() method is as follow:

Example-

Output -