Iterators

• An iterator is an Object that enables to cycle through a collection , obtain or remove elements.
• Before you can access a collection through an iterator , you must obtain 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 ,  we can acccess each elements in the collection , one element at a time.
• The iterator class provides the following methods-
• hasNext() – Returns true if there is atleast one or more element ;Otherwise it return false.
• next() – Return the next object & advance the iterator.
• remove() – Removes the last object that was returned by the next form the collection.
• Iterator class must be imported from java.util package.

Example-
import java.util.Iterator;
import java.util.LinkedList;
public class Myclass{
     public static void main(String args[]){
       LinkedList<String> animals = new LinkedList<String>();
       animals.add("fox");
       animals.add("cat");
       animals.add("dog");
       animals.add("rat");
       Iterator<String> it = animals.iterator();
       String value = it.next();
       System.out.println(value);
   }
}
output-
fox

• it.next() returns the first element in the list and then moves the iterator on to the next element.
• Each time you call it.next() , the iterator moves to the next element of the list
• Typically , iterator are used in loops. At each iteration of the loop , you can access the corresponding list element.

• Example-
  import java.util.Iterator;
  import java.util.LinkedList;
  public class Myclass{
       public static void main(String args[]){ 
              LinkedList<String> animals = new LinkedList<String>(); 
              animals.add("fox"); 
              animals.add("cat"); 
              animals.add("dog"); 
              animals.add("rat"); 
              Iterator<String> it = animals.iterator(); 
              while(it.hasNext()){
                    String value = it.next();
                    System.out.println(value);
           }
  }
  Output-
  fox
  cat
  dog
  rat