public boolean addEdge(E e) {
    V a = e.getVertexA();
    if (a == null) {
      return false;
    }
    V b = e.getVertexB();
    if (b == null) {
      return false;
    }
    int idA = a.getId();
    int idB = a.getId();
    /* Ueberpruefen, ob Knoten in Graph */
    Integer idxA = vertexIndex.get(idA);
    Integer idxB = vertexIndex.get(idB);
    if (idxA == null || idxB == null) {
      return false;
    }
    return adjList.get(vertexIndex.get(idA)).add(e);
  }