I'm having a problem with this program I want to write. I have bipartite graph and I first want to store vertex from the left side in array, and then under that every vertex I want to save all the edges, that go from that vertex to another (the number of edges varies). I've tries with ArrayList of ArrayList's but I have problems, with searching for existing vertices in the array. So if anyone knows for a better way, or knows how to realize that with ArrayList I would be very grateful.