How to create a graph using Java

How to create a graph using Java

How to create a graph using Java  

Let's see simple graph creation using core java and printing all the vertex along with list of edges which goes from that particular Vertex.

public class MyGraph {

 public static void main(String[] args) {
  
  /* Initilize graph with 5 vertex and as 
   * going to be directed graph
   */
  
  Graph myGra = new Graph(5, "directed");
  
  /*
   * Add vertex 
   */
  myGra.addVertex("A");
  myGra.addVertex("B");
  myGra.addVertex("C");
  myGra.addVertex("D");
  myGra.addVertex("E");
  
  /*
   * Add edges between each vertex and their distance 
   */
  myGra.addEdge("A", "B",5);
  myGra.addEdge("A", "E",1);
  myGra.addEdge("B", "C",2);
  myGra.addEdge("C", "D",2);
  myGra.addEdge("E", "D",2);
  myGra.addEdge("E", "A",2);
  
  // Print the created graph
  myGra.printMyGraph();
  
 }
}

public class Graph {

 // Graph direction (directed / undirected graph)
 private boolean undirected = true;
 
 // No. of vertex in the graph
 private Vertex[] arrayOfVertex;
 
 private int indexCounter = 0;
 
 // Constructor to create graph vertex 
 public Graph(int noOfVertex, String graphType) {
  if (graphType.equalsIgnoreCase("directed")) {
   this.undirected = false;
  }
  arrayOfVertex = new Vertex[noOfVertex];
 }
 
 // Vertex class
 class Vertex {
  // Name of the Vertex
  private String name;
  
  // Holds the list of all edges from current vertex 
  private Edge edge;

  // Create vertex 
  public Vertex(String name, Edge aNode) {
   this.name = name;
   this.edge = aNode;
  }
 }
 
 // Edge between 2 Vertex
 class Edge {
  // Destination vertex Id
  private int vertexId;
  
  // In list point to next edge if its else null 
  private Edge next;
  
  // Weight of current edge
  private int weight;

  // Create edge
  public Edge(int vertexId, Edge next, int weight) {
   this.vertexId = vertexId;
   this.next = next;
   this.weight = weight;
  }
 }

 // Adding Vertex 
 public void addVertex(String vertexName) {
  arrayOfVertex[indexCounter] = new Vertex(vertexName, null);
  indexCounter++;
 }

 // Adding Edge
 public void addEdge(String sVertex, String dVertex, int weight) {
  int sId = indexOfName(sVertex);
  int dId = indexOfName(dVertex);

  /*
   * Find source and destination vertexId and create new Edge and 
   * point it to source edge link
   */
  arrayOfVertex[sId].edge = new Edge(dId, arrayOfVertex[sId].edge, weight);
  
  /*
   * If undirected then create 2 edge's between source and destination and 
   * destination to source 
   */
  if (undirected) {
   arrayOfVertex[dId].edge = new Edge(sId, arrayOfVertex[dId].edge, weight);
  }
 }

 /*
  * Getting indexId of given vertex name
  */
 private int indexOfName(String name) {
  for (int v = 0; v < arrayOfVertex.length; v++) {
   if (arrayOfVertex[v].name.equals(name)) {
    return v;
   }
  }
  return -1;
 }

 /*
  * Print the graph in vertex order and listing all outgoing edges from that vertex
  */
 public void printMyGraph() {
  System.out.println("VERTEX\t----> EDGES WITH WEIGHT");
  for (int v = 0; v < arrayOfVertex.length; v++) {
   System.out.print(arrayOfVertex[v].name +" \t ----> ");
   for (Edge aNode = arrayOfVertex[v].edge; aNode != null; aNode = aNode.next) {
    System.out.print( "<==>"+ arrayOfVertex[aNode.vertexId].name + ":" + aNode.weight);
   }
   System.out.println();
  }

 }
}

OUTPUT:

VERTEX         ----> EDGES WITH WEIGHT
A          ----> <==>E:1<==>B:5
B          ----> <==>C:2
C          ----> <==>D:2
D          ----> 
E          ----> <==>A:2<==>D:2