public E getEdge(V sourceVertex, V targetVertex) { E res = null; if (g1.containsVertex(sourceVertex) && g1.containsVertex(targetVertex)) { res = g1.getEdge(sourceVertex, targetVertex); } if ((res == null) && g2.containsVertex(sourceVertex) && g2.containsVertex(targetVertex)) { res = g2.getEdge(sourceVertex, targetVertex); } return res; }