AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph();
AdjacencyMatrixVertex v1 = new AdjacencyMatrixVertex(graph, "A");
AdjacencyMatrixVertex v2 = new AdjacencyMatrixVertex(graph, "B");
AdjacencyMatrixVertex v3 = new AdjacencyMatrixVertex(graph, "C");
AdjacencyMatrixVertex v4 = new AdjacencyMatrixVertex(graph, "D");
graph.addVertex("A");
graph.addVertex("B");
graph.addVertex("C");
graph.addVertex("D");
graph.addEdge("A", "B");
graph.addEdge("A", "C");