Java Program to Implement the graph data structure

Example: Implement Graph Data Structure

class Graph {

  // inner class
  // to keep track of edges
  class Edge {
    int src, dest;
  }

  // number of vertices and edges
  int vertices, edges;

  // array to store all edges
  Edge[] edge;

  Graph(int vertices, int edges) {
    this.vertices = vertices;
    this.edges = edges;

    // initialize the edge array
    edge = new Edge[edges];
    for(int i = 0; i < edges; i++) {

      // each element of the edge array
      // is an object of Edge type
      edge[i] = new Edge();
    }
  }

  public static void main(String[] args) {

    // create an object of Graph class
    int noVertices = 5;
    int noEdges = 8;
    Graph g = new Graph(noVertices, noEdges);

    // create graph
    g.edge[0].src = 1;   // edge 1---2
    g.edge[0].dest = 2;

    g.edge[1].src = 1;   // edge 1---3
    g.edge[1].dest = 3;

    g.edge[2].src = 1;   // edge 1---4
    g.edge[2].dest = 4;

    g.edge[3].src = 2;   // edge 2---4
    g.edge[3].dest = 4;

    g.edge[4].src = 2;   // edge 2---5
    g.edge[4].dest = 5;

    g.edge[5].src = 3;   // edge 3---4
    g.edge[5].dest = 4;

    g.edge[6].src = 3;   // edge 3---5
    g.edge[6].dest = 5;

    g.edge[7].src = 4;   // edge 4---5
    g.edge[7].dest = 5;

    // print graph
    for(int i = 0; i < noEdges; i++) {
      System.out.println(g.edge[i].src + " - " + g.edge[i].dest);
    }

  }
}

Output

1 - 2
1 - 3
1 - 4
2 - 4
2 - 5
3 - 4
3 - 5
4 - 5

In the above example, we have implemented the graph data structure in Java. To learn more about graphs, visit Graph Data Structure.