Java partially ordered Collection

Question

I am looking for a Java implementation of a data structure which holds a collection of elements for which a partial ordering is defined, and which allows on

Answer 1

Would a directed acyclic graph be sufficiently general for your needs? I know that this doesn't capture posets generally, but you mentioned wanting to exclude graph cycles.

If so you might look at JGraphT: http://jgrapht.org/

There's a graph iterator for topological sorts.

Note that the directed graphs aren't java.util.Collections, but you can grab the vertices, which are a java.util.Set. If you need the data structure itself to be a Collection, you could probably wrap a JGraphT directed graph with a thin wrapper that is a Collection, treating the vertices as elements.

The potential drawback here is that you have to create edges explicitly, which may or may not be acceptable for your application.