CODEWITHSUNDEEP
javaclassobjectlinked-listinstance
satnam
satnam

Reputation: 1425

Java - What happens when we create a data type of type class in its own class?

I'm studying linked lists. Again and again I see code which declares a data type of class in the body of the that very class. Here is an example from the book Cracking the coding interview (creating a linked list)

class Node {
    Node next = null;
    int data;
    public Node(int d) { data = d; }
    void appendToTail(int d) {
        Node end = new Node(d);
        Node n = this;
        while (n.next != null) { n = n.next; }
        n.next = end;
    }
}

In the second line - as you can see 'next' is an instance variable of the type Node, is its own class.

My question is, if I create an instance of the class Node (say X) - 

Node X = new Node(10);

The books say that compiler will automatically reserve space for its instance variables (data and next) even if they are not initiated. The (int data = 10) is clearly handled in the constructor, but what happens with next? Seems to me like X will have infinite number of 'next' nodes inside it, because X will have a node inside it named next. And then since every node is supposed to have a data and next part, then next will have its own copy of data and next inside it, and so on and so on.....leading to something like this...

enter image description here

Upvotes: 3

Views: 291

Answers (1)

Ideasthete
Ideasthete

Reputation: 1541

The 'next' Node is simply a reference to a Node object. The fact that space is reserved for the reference to that Node does not mean that a whole new Node is created with sub-Nodes, it just means that the original Node has enough 'room' to store a reference to the other Node. Since 'next' initially has a reference to null, there is 'nothing there' until you initialize a Node and store a reference to it in 'next'.

Basically, a reference to a Node is not the same as a Node.

See Oracle's Documentation on Types, Values and Variables for more information.

Upvotes: 6

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