Java: how to represent graphs?

Question

I'm implementing some algorithms to teach myself about graphs and how to work with them. What would you recommend is the best way to do that in Java? I was thinking something like this:

public class Vertex {

    private ArrayList<Vertex> outnodes; //Adjacency list. if I wanted to support edge weight, this would be a hash map.

    //methods to manipulate outnodes
}

public class Graph {
    private ArrayList<Vertex> nodes;
    //algorithms on graphs
}

But I basically just made this up. Is there a better way?

Also, I want it to be able to support variations on vanilla graphs like digraphs, weighted edges, multigraphs, etc.

Answer 1

Each node is named uniquely and knows who it is connected to. The List of connections allows for a Node to be connected to an arbitrary number of other nodes.

public class Node {
    public String name;
    public List<Edge> connections;
}

Each connection is directed, has a start and an end, and is weighted.

public class Edge {
    public Node start;
    public Node end;
    public double weight;
}

A graph is just your collection of nodes. Instead of List<Node> consider Map<String, Node> for fast lookup by name.

public class Graph {
    List<Node> nodes;
}