What is marker Interface in java?

Marker Interface doesn't have any method or field or constant declared within it. So a marker interface is an empty interface.

Example :

• Serializable, 
• Cloneable, 
• RandomAccess interface and 
• Remote interface

Now one question that would immediately pop-up in your mind is,

Why would one declare an empty interface? 
What good is it of?

In general a common belief is that a marker interface is generally used to send some kind of signal to the JVM and instructs JVM to  treat the class implementing it in a special way.

Like, when a class implements Cloneable marker interface, it signals the compiler that the class allows creation of clones of its objects.

Generally, a marker interface is used with the instanceof operator to check if a reference type variable refers to an object whose class implements the marker interface.


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• Class variable vs instance variable
• iterator vs list iterator
• Why String is immutable in java?

Traverse ArrayList using Enumeration

package javaRadarArrayList;

import java.util.ArrayList;

import java.util.Collections;

import java.util.Enumeration;

import java.util.ListIterator;

public class EnumerationTraversal {

      public static void main(String[] args) {

            //create Array List

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

            //Add elements to ArrayList

            javaRadarList.add("Java");

            javaRadarList.add("Jquery");

            javaRadarList.add("Spring");

            javaRadarList.add("Hibernate");

            javaRadarList.add("EJB");

            //creating enumeration to traverse over javaRadarList

            Enumeration<String> listEnumerator = Collections.enumeration(javaRadarList);

            System.out.println("List traversal using Enumeration");

            while(listEnumerator.hasMoreElements()){

                  System.out.println(listEnumerator.nextElement());

            }

      }

}

OUTPUT:

List traversal using Enumeration

Java

Jquery

Spring

Hibernate

EJB

Remove element from array list

package javaRadarArrayList;

import java.util.ArrayList;

public class RemoveAtIndex {

      public static void main(String[] args) {

            //create Array List

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

            //Add elements to ArrayList

            javaRadarList.add("Java");

            javaRadarList.add("Jquery");

            javaRadarList.add("Spring");

            javaRadarList.add("Hibernate");

            javaRadarList.add("EJB");

           

            System.out.println("Before Removal");

            for(String list : javaRadarList){

                  System.out.println(list);

            }

           

            //Remove element from 2nd position

            javaRadarList.remove(1);

           

            System.out.println("After Removal");

            for(String list : javaRadarList){

                  System.out.println(list);

            }

      }

}

OUTPUT:

 Before Removal

Java

Jquery

Spring

Hibernate

EJB

After Removal

Java

Spring

Hibernate

EJB

Compare the result and you will find that element at 2nd position(Jquery) will not appear in After Removal result.

Remove element from linked list

package javaRadarLinkedList;

import java.util.LinkedList;

public class RemoveAtIndex {

      public static void main(String[] args) {

            //create Array List

            LinkedList<String> javaRadarList = new LinkedList<String>();

            //Add elements to ArrayList

            javaRadarList.add("Java");

            javaRadarList.add("Jquery");

            javaRadarList.add("Spring");

            javaRadarList.add("Hibernate");

            javaRadarList.add("EJB");

           

            System.out.println("Before Removal");

            for(String list : javaRadarList){

                  System.out.println(list);

            }

           

            //Remove element from 2nd position

            javaRadarList.remove(1);

           

            System.out.println("After Removal");

            for(String list : javaRadarList){

                  System.out.println(list);

            }

      }

}

OUTPUT:

Before Removal

Java

Jquery

Spring

Hibernate

EJB

After Removal

Java

Spring

Hibernate

EJB

Traverse Linked list using iterator

package javaRadarLinkedList;

import java.util.Iterator;

import java.util.LinkedList;

public class ItrTraversal {

      public static void main(String[] args) {

            //create Linked List

            LinkedList<String> javaRadarList = new LinkedList<String>();

            //Add elements to LinkedList

            javaRadarList.add("Java");

            javaRadarList.add("Jquery");

            javaRadarList.add("Spring");

            javaRadarList.add("Hibernate");

            javaRadarList.add("EJB");

            //creating iterator to traverse over javaRadarList

            Iterator<String> listIterator = javaRadarList.iterator();

            System.out.println("Traversal in forward direction");

            while(listIterator.hasNext()){

                  System.out.println(listIterator.next());

            }

      }

}

OUTPUT:

Traversal in forward direction

Java

Jquery

Spring

Hibernate

EJB 

Traverse linked list using enumeration

package javaRadarLinkedList;

import java.util.Collections;

import java.util.Enumeration;

import java.util.LinkedList;

public class EnumerationTraversal {

      public static void main(String[] args) {

            //create Linked List

            LinkedList<String> javaRadarList = new LinkedList<String>();

            //Add elements to LinkedList

            javaRadarList.add("Java");

            javaRadarList.add("Jquery");

            javaRadarList.add("Spring");

            javaRadarList.add("Hibernate");

            javaRadarList.add("EJB");

            //creating iterator to traverse over javaRadarList

            Enumeration<String> listEnumerator = Collections.enumeration(javaRadarList);

            System.out.println("List traversal using Enumeration");

            while(listEnumerator.hasMoreElements()){

                  System.out.println(listEnumerator.nextElement());

            }

      }

}

Traverse linked list using ListIterator

package javaRadarLinkedList;

import java.util.LinkedList;

import java.util.ListIterator;

public class ListItrTraversal {

      public static void main(String[] args) {

            //create Linked List

            LinkedList<String> javaRadarList = new LinkedList<String>();

            //Add elements to LinkedList

            javaRadarList.add("Java");

            javaRadarList.add("Jquery");

            javaRadarList.add("Spring");

            javaRadarList.add("Hibernate");

            javaRadarList.add("EJB");

            //creating list iterator to traverse over javaRadarList

            ListIterator<String> listIterator = javaRadarList.listIterator();

           

            System.out.println("Traversal in forward direction");

            while(listIterator.hasNext()){

                  System.out.println(listIterator.next());

            }

           

            System.out.println("Traversal in backward direction");

            while(listIterator.hasPrevious()){

                  System.out.println(listIterator.previous());

            }

      }

}

 OUTPUT:

Traversal in forward direction

Java

Jquery

Spring

Hibernate

EJB

Traversal in backward direction

EJB

Hibernate

Spring

Jquery

Java