public boolean isEdgeExists(int i, int j) {
		if (i < vertexNum && j < vertexNum && i >= 0 && j >= 0) {
			if (i == j) return false;
			if (i > j) { //exchange i & j
				int k = i; i = j; j = k; 
			}
			if (vector[i] == null) vector[i] = new Vector<Integer>(8);
			for (int q = 0; q < vector[i].size(); q++) {
				if ((vector[i].get(q)).intValue() == j) {
					System.out.println(" An edge exists between vertex" + i + " and " + " vertex " + j);
					return true;
				}
			}
		}
		return false;
	}