Iterator pattern or Cursor

Iterator pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

The iterator pattern decouples algorithms from containers; in some cases, algorithms are necessarily container-specific and thus cannot be decoupled.

package designpattern.iterator;

public interface Iterator {

      public boolean hasNext();

      public Object next();

}

public interface IContainer {

      public Iterator getIterator();

}

public class Mp3Player implements IContainer {

      private int size;

      private int index;

      private Object songsList[];

     

      public Mp3Player(int size) {

            songsList = new Object[size];

            this.size = size;

            index = 0;

      }

     

      @Override

      public Iterator getIterator() {

            return new SongsIterator();

      }

      private class SongsIterator implements Iterator {

            int index;

            @Override

            public boolean hasNext() {

                  if(index<songsList.length) {

                        return true;

                  }

                  return false;

            }

            @Override

            public Object next() {

                  if(this.hasNext()) {

                        return songsList[index++];

                  }

                  return null;

            }

      }

      public void addName(Object string) {

            if(index<size) {

                  songsList[index] = string;

            }

            index++;

      }

}

public class IteratorPatternTest {

      public static void main(String[] args) {

            Mp3Player mp3Player = new Mp3Player(2);

            mp3Player.addName("Is it love");

            mp3Player.addName("Feel me");

           

            Iterator iter = mp3Player.getIterator();

            while(iter.hasNext()) {

                  String name = (String) iter.next();

                  System.out.println("Song : " + name);

            }    

      }

}

Output:

Song : Is it love

Song : Feel me

https://en.wikipedia.org/wiki/Iterator_pattern