I'm going through a code for linked list operations on the internet and I found the following code snippet which i cannot understand.

class Node 
{
    int data;
    Node node; //reference to the next node
    :
    :
}

I've learned that Node node; line is the reference to the next node as nodes of linked list contain data and address of the next node.

But I cannot understand the concept behind it.

Can anybody explain what is the java concept/ theory if a variable is defined with the class name as it's Data Type?

CodePudding user response：

Can anybody explain what is the java concept/ theory if a variable is defined with the class name as it's Data Type?

If I understand your question correctly, you're confused by declaring a variable of the same type as the class it's in, correct? The fact that the class Node has an instance of itself as a variable Node node?

Well, there is no "theory or concept" here. A class can define variables of any known type. The class Node, by being defined is a known type. Thus it can declare variables of that type, even within itself.

This is use primarily in data structures that have some kind of nesting structure. You already gave one example, a Node that references the next node.

You could also have a bidirectional linked list:

class Node {
   Node previous;
   Node next;
}

You could have a Directory class that represents a folder structure:

class Directory {
   Directory[] subDirectories;
   File[] files;
}

Or a JSONObject class that holds a key/value pair of nested JSONObjects

class JSONObject {
    Map<String, JSONObject> children;
}

Etc, etc.

CodePudding user response：

Can anybody explain what is the java concept/ theory if a variable is defined with the class name as it's Data Type?

There is no such concept or theory.

From the Java language perspective, a variable name can be anything as long as it conforms to the required syntax.

From a Java style perspective, a variable name should convey meaning to the reader. But it is up to the author of the code to decide how to convey the meaning and what / how much meaning needs to be (explicitly) conveyed.

In this case, the author has decided that they will simply use node as the variable name. That conveys no meaning in addition to the obvious: it is a "node". The actual intended meaning for this variable is conveyed by the comment:

//reference to the next node

but you could probably figure that out by reading the rest of the code in the Node class and/or the code that uses the class.

^{For what it us worth, I would probably called the variable next rather than node. But I probably would not have called out the author's choice as incorrect in a code review.}

As a general statement, there are differing opinions on what and how much meaning variable names should convey. But there are no generally accepted rules. So you need to be prepared read the code rather than relying on the variable names.

This can be a problem if the code is complicated, or if you are trying to a learn about a new (to you) kind of data structure. But in the latter case, the solution may be to find a better code to learn from.

For instance, any good textbook on Data Structures will have example code for linked lists. The code should be better written and should have accompanying text to explain it. And if you don't want to buy / borrow a textbook, you can probably find better example code on the internet to learn from.

CodePudding user response：

//Node holds reference to Node
class Node{
    Node link;
    int info;
    public Node(){
    }
    public Node(int info){
        this.info=info;
    }
    public String toString(){
        return Integer.toString(info);
    }

}
class Linked{
    Node head;//head reference denoted the beginning of the linkedlist
    private int size=0;
    public void add(int info){
        if (size==0){
            head=new Node(info);
        }else{
            Node temp=head;
            while(temp.link!=null){
                temp=temp.link;
            }
            temp.link=new Node(info);
        }
        size  ;
    }
    public String toString(){
        String str="";
        var temp=head;
        while(temp!=null){
            str =temp.info " ";
            temp=temp.link;
        }
        return str;
    }
    public static void main(String ... $){
        Linked link=new Linked();
        link.add(10);
        link.add(555);
        link.add(55);
        var out=System.out;
        out.println(link);
    }

}