Graph Adjacency list Representation

GraphAdjacencyListRepresentation.java

import java.util.LinkedList;

public class GraphAdjacencyListRepresentation {
    public static void main(String[] args) throws GraphRep.GraphException {
       GraphRep graphRep = new GraphRep(6);
        graphRep.addVertexTo(new GraphNode(4), new GraphNode(5));
        graphRep.addVertexTo(new GraphNode(4), new GraphNode(1));
        graphRep.addVertexTo(new GraphNode(4), new GraphNode(6));

        graphRep.addVertexTo(new GraphNode(5), new GraphNode(1));
        graphRep.addVertexTo(new GraphNode(5), new GraphNode(7));

        graphRep.addVertexTo(new GraphNode(6), new GraphNode(1));
        graphRep.addVertexTo(new GraphNode(6), new GraphNode(2));
        graphRep.addVertexTo(new GraphNode(1), new GraphNode(2));
        graphRep.printGraph();

        //     4------------5--------7
        //     |\           |
        //     |  \         |
        //     |    \       |
        //     |      \     |
        //     |        \   |
        //     |          \ |
        //     6------------1
        //      \          /
        //       \        /
        //        \      /
        //         \    /
        //          \  /
        //           2


    }
    static class GraphNode {
        int data;

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

    static class GraphRep {
        LinkedList<GraphNode>[] adjList;
        int count = 0;

        public GraphRep(int nodesNumber) {
            adjList = new LinkedList[nodesNumber];
        }

        public void addVertexTo(GraphNode source, GraphNode destination) throws GraphException {
            insert(source, destination);
            insert(destination, source);

        }

        private void insert(GraphNode source, GraphNode destination) throws GraphException {
            if (count >= adjList.length) {
                throw new GraphException("Out of bound check The right number of your vertices ");
            }
            int index = vertexExist(source);
            if (index != -1) {
                LinkedList<GraphNode> graphNodes = adjList[index];
                graphNodes.addLast(destination);
            } else {
                adjList[count] = new LinkedList<>();
                adjList[count].addFirst(source);
                adjList[count].addLast(destination);
                count++;
            }
        }

        private int vertexExist(GraphNode source) {
            for (int i = 0; i < adjList.length; i++) {
                LinkedList<GraphNode> graphNodes = adjList[i];
                if (graphNodes != null && graphNodes.getFirst().data == source.data) {
                    return i;
                }
            }
            return -1;
        }

        public void printGraph() {
            for (LinkedList<GraphNode> graphNodes : adjList) {
                System.out.println("Nodes For " + graphNodes.poll().data);
                while (!graphNodes.isEmpty()) {
                    System.out.print(" " + graphNodes.poll().data);
                }
                System.out.println("");
                System.out.println("----------");
            }
        }

        class GraphException extends Exception {
            public GraphException(String message) {
                super(message);
            }
        }

    }
}