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A '''node''' is an abstract basic unit used to build linked [[data structure]]s such as [[tree data structure|trees]], [[linked list]]s, and computer-based representations of [[graph (data structure)|graphs]]. Each node contains some [[data]] and possibly links to other nodes. Links between nodes are often implemented by [[Data pointer|pointer]]s or [[Reference (computer science)|reference]]s.

A node can be thought of as a logical placeholder for some data. It is a memory block which contains some data unit and perhaps references to other nodes, which in turn contain data and perhaps references to yet more nodes. By forming chains of interlinked nodes, very large and complex data structures can be formed.

Nodes are conceptually similar to [[vertex (graph theory)|vertices]], which are elements of a [[Graph (mathematics)|graph]].

== Examples of Abstract Node Implementation ==

A node containing a single reference field.

  '''class''' ''Node'' {
     data ''// The data being stored in the node''
     next ''// A [[Reference (computer science)|reference]] to the next node, null if last node''
  }

Here three such nodes form a singly-linked list of length 3.

<br>[[Image:Singly-linked-list.svg]]

<br>

A node containing two reference fields.

  '''class''' ''Node'' {
     data ''// The data being stored in the node''
     previous ''// A [[Reference (computer science)|reference]] to the previous node, null if first node''
     next ''// A [[Reference (computer science)|reference]] to the next node, null if last node''
  }

Here three such nodes form a doubly-linked list of length 3.



&nbsp;&nbsp;&nbsp; [[Image:Doubly-linked-list.svg]]

<br>(...Java Example Link...)

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