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 somethi

Answer 1

If you need weighted edges and multigraphs, you might want to add another class Edge.

I would also recommend using generics to allow specifying which sub-class of Vertex and Edge are currently used. For example:

public class Graph<V extends Vertex> {
List<V> vertices;
...
}

When it comes to implementing graph algorithms, you could also define interfaces for your graph classes on which the algorithms can operate, so that you can play around with different implementations of the actual graph representation. For example, simple graphs that are well-connected might be better implemented by an adjacency matrix, sparser graphs might be represented by adjacency lists - it all depends...

BTW Building such structures efficiently can be quite challenging, so maybe you could give us some more details on what kind of job you would want to use them for? For more complex tasks I would suggest you have a look at the various Java graph libraries, to get some inspiration.

Answer 2

Time ago I had the same problem and did my own implementation. What I suggest you is to implement another class: Edge. Then, a Vertex will have a List of Edge.

public class Edge {
    private Node a, b;
    private directionEnum direction;     // AB, BA or both
    private int weight;
    ...
}

It worked for me. But maybe is so simple. There is this library that maybe can help you if you look into its code: http://jgrapht.sourceforge.net/

Answer 3

Even at the time of this question, over 3 years ago, Sage (which is completely free) existed and was pretty good at graph theory. But, in 2012 it is about the best graph theory tool there is. Thus, Sage already has a huge amount of graph theory material built in, including other free and open source stuff that is out there. So, simply messing around with various things to learn more is easy as no programming is required.

And, if you are interested in the programming part as well, first Sage is open source so you can see any code that already exists. And, second, you can re-program any function you want if you really want to practice, or you can be the first to program something that does not already exist. In the latter case, you can even submit that new functionality and make Sage better for all other users.

At this time, this answer may not be that useful to the OP (since it has been 3 years), but hopefully it is useful to any one else who sees this question in the future.

Answer 4

Adjacency List implementation of Graph is appropriate for solving most of the graph related problems.

Java implementation of the same is here on my blog.

Answer 5

Take a look at the http://jung.sourceforge.net/doc/index.html graph library. You can still practice implementing your own algorithms (maybe breadth-first or depth-first search to start), but you don't need to worry about creating the graph structure.

Answer 6

Why not keep things simple and use an adjacency matrix or an adjacency list?