Java Code of AdjacencyList representation of Graph

We strongly recommend to refer below post before moving on to this post.

Introduction of graph

An undirected graph:

Below is the java code of adjacency list representation of Graph

//A java code to demonstrate adjacency list representation of an undirected graph
public class GraphRepresentation {

 // class to represent an adjacency list node of graph
 class GraphNode {
  int key;
  GraphNode next;

  public GraphNode(int key) {
   this.key = key;
  }
 }

 // class to represent a graph. A graph is an array of adjacency list of
 // GraphNode
 class Graph {
  // v is number of vertex in graph
  int v;
  GraphNode arr[];

  public Graph(int v) {
   this.v = v;
   arr = new GraphNode[v];

  }

  // add an edge in an undirected graph
  public void addEdge(int i, int j) {
   GraphNode node = new GraphNode(j);
   node.next = this.arr[i];
   this.arr[i] = node;

   node = new GraphNode(i);
   node.next = this.arr[j];
   this.arr[j] = node;

  }

  // a function to print adjacency list representation of a graph
  public void printGraph() {
   for (int i = 0; i < this.v; i++) {
    GraphNode gCrawl = this.arr[i];
    System.out.print("Adjacency list of array " + i + "\nhead");
    while (gCrawl != null) {
     System.out.print("-->" + gCrawl.key);
     gCrawl = gCrawl.next;
    }
    System.out.println();
   }
  }

 }

 public static void main(String[] args) {
  // create a graph of which have 5 vertices.
  int v = 5;
  GraphRepresentation gr = new GraphRepresentation();
  Graph graph = gr.new Graph(v);
  // add edges of graph
  graph.addEdge(0, 1);
  graph.addEdge(0, 4);
  graph.addEdge(1, 2);
  graph.addEdge(1, 4);
  graph.addEdge(2, 3);
  graph.addEdge(2, 4);
  graph.addEdge(3, 4);
  // print adjacency list representation of above graph
  graph.printGraph();
 }
}

Output of above program is shown below:

Adjacency list of array 0
head-->4-->1
Adjacency list of array 1
head-->4-->2-->0
Adjacency list of array 2
head-->4-->3-->1
Adjacency list of array 3
head-->4-->2
Adjacency list of array 4
head-->3-->2-->1-->0

find the above working code from git.