Keeping the collection of objects without using Collections or Arrays

Hey Guys,

One of my colleague asked me how can I keep a collection of Objects without using any Collection framework or Arrays and neither Maps (further more Maps are not Collections, since they never implement Collections interface)?

At first I was numb, since I am unable to think how is it possible to have a group of objects without using Collections or Arrays or Maps, then I just got an idea when we implemented the Linked Lists using Node traversals in C Language like this,

#include <stdlib.h>

struct node {
  int x;
  struct node *next;
};

int main()
{
    /* This will be the unchanging first node */
    struct node *root;      

    /* Now root points to a node struct */
    root = malloc( sizeof(struct node) ); 

    /* The node root points to has its next pointer equal to a null pointer 
       set */
    root->next = 0;  
    /* By using the -> operator, you can modify what the node,
       a pointer, (root in this case) points to. */
    root->x = 5;     
}

//courtesy : Linked List in C

Using the same concept I proposed this solution, the solution is pretty much same as the concept of  C, here what I did;

public class Data{

 private int a;
 private Data next;

 public int getA() {
  return a;
 }

 public void setA(int a) {
  this.a = a;
 }

 public Data getNext() {
  return next;
 }

 public void setNext(Data next) {
  this.next = next;
 }

 @SuppressWarnings("unused")
 public static void main(String[] args) {
  
  Data d1 = new Data();
   d1.setA(1);
  Data d2 = new Data();
   d2.setA(2);
   d2.setNext(null);
   
  d1.setNext(d2);
  
  Data start = d1;
  Data startCopy = start;
  
  while(start!=null){
   System.out.println(start.getA());
   start = start.getNext();
  }
 }

}

In this way we can make a Doubly Linked List, with the functionalities like add(), next(), prev(), find(int), get(int), getFromEnd(int), getFromStart(int) and so on.