在堆栈数据结构上存储新元素时，.next如何工作？ 【JAVA]

Question

I'm learning to implement a Stack and I'm struggling to understand what .next REALLY means. I've seen it in many data structures and it's obvious what its purpose is until I actually ask myself if it is a keyword or how it functions. It looks like it is an object but it seems to be acting like a pointer (like in a LinkedList) to each of the item objects that are created.

Please help in any way you can to shed some light on my confusion!

class Item {
    intdata;
    Item next;

    public Item(int data) {
        this.data = data;
    }
}

public class Stack {

   private Item top;

   public void push(int data) {
       if (null == top) {
           top = new Item(data);
       } else {
           Item item = new Item(data);
           item.next = top;
           top = item;
       }
   }
}

Answer 1

Just think about this, if you have two initial raw data 1 and 2 . And, on the other hand, I tell you to map all the natural numbers as Item s and then put them into a stack.

Considering, you might just come up with let us say, two Item objects currently unrelated as -

Item item1 = new Item(1);

and

Item item2 = new Item(2);

and then as you put them into the Stack , you push item1 and you would eventually push item2 . There could similarly be N number of data that you might have pushed.

And now to make you a little smarter, I would ask you to remember while you pop an element from that Stack as to what could be the next element possible, just to see if we might even need to pop more or not from that stack. [Let's say need be to display only elements greater than 5]

That is where the relation between the two items would become useful. You make one item point to the next while pushing them into the stack to keep a reference of the same. And so you do:-

item2.setNext(item1); // using setter for 'next'

Which eventually means while accessing item2 you can actually be aware of the next Item it points to ie item1 .

PS : The same implementation as item2.setNext(item1) is generalized in your code's push method which accepts a data and creates a new instance of Item every time its called.