public T getEdge(int i, int j) throws IllegalArgumentException {
		// check the passed vertex indizes
		if (i < 0 || i >= numberOfVertices || j < 0 || j >= numberOfVertices) {
			String errorMessage =
				"Allows vertex indizes are 0.."
				+ (numberOfVertices - 1) + ".";
			
			throw new IllegalArgumentException(errorMessage);
		}
		
		for (T e : adjacencyList[i]) {
			if (e.getTarget() == j) {
				return e;
			}
		}
		
		return null;
	}