Difference Between Iterator and Enumeration in Java

Iterator and Enumeration are both cursors to traverse and access elements from the collection. They both belong to the collection framework. Enumeration was added in JDK1.0 and Iterator in JDK 1.2 version in the collection framework. 

Java Enumeration

Enumeration: An enumeration is a special "class" that indicates a collection of constants. Enumeration can't make structural changes in the collection because it has read-only access to its elements. It has the following methods ?

• hasMoreElements(): The hasMoreElements() method checks to see if more elements exist in the underlying collection class
• nextElement(): The nextElement() method returns the next elements from the collection

Example of Enumeration

The following is the example of Enumeration ?

import java.util.*;

public class EnumerationExample {
   public static void main(String args[]) {
      List list = new ArrayList(Arrays.asList(new String[] {"Apple", "Cat", "Dog", "Rat"}));
      Vector v = new Vector(list);
      delete(v, "Dog");
   }

   private static void delete(Vector v, String name) {
      Enumeration e = v.elements();
      while (e.hasMoreElements()) {
         String s = (String) e.nextElement();
         if (s.equals(name)) {
            v.remove(name); // This causes ConcurrentModificationException in some JVMs
         }
      }

      // Display the names
      System.out.println("The names are:");
      e = v.elements();
      while (e.hasMoreElements()) {
         System.out.println(e.nextElement());
      }
   }
}

The output of the above Java program is ?

The names are:
Apple
Cat
Rat

Java Iterator

Iterator: An iterator can read and remove elements in the collection. It has the following methods ?

• hasNext(): The hasNext() method checks to see if more objects exist in the underlying collection class.
• next(): The next() method returns the next object from the collection.
• remove(): The remove() method removes the last element from the collection that was returned by the next() method.
• forEachRemaining(): The forEachRemaining() method performs a function on all remaining elements in the collection.

Example of Iterator

The following is the example of Iterator ?

import java.util.*;

public class IteratorExample {
   public static void main(String args[]) {
      List<String> list = new ArrayList<>(Arrays.asList("Apple", "Cat", "Dog", "Rat"));
      Vector<String> v = new Vector<>(list);
      delete(v, "Dog");
   }

   private static void delete(Vector<String> v, String name) {
      Iterator<String> i = v.iterator();
      while (i.hasNext()) {
         String s = i.next();
         if (s.equals(name)) {
            i.remove(); // Safe removal
         }
      }

      // Display the names
      System.out.println("The names are:");
      i = v.iterator();
      while (i.hasNext()) {
         System.out.println(i.next());
      }
   }
}

The output of the above Java program is ?

The names are:
Apple
Cat
Rat

Difference between Iterator and Enumeration

The following table shows the difference between Iterator and Enumeration ?