Question

My Hashtable in Java would benefit from a value having a tuple structure. What data structure can I use in Java to do that?

Hashtable<Long, Tuple<Set<Long>,Set<Long>>> table = ...

Answer 1

I don’t think there is a general purpose tuple class in Java but a custom one might be as easy as the following:

public class Tuple<X, Y> { 
  public final X x; 
  public final Y y; 
  public Tuple(X x, Y y) { 
    this.x = x; 
    this.y = y; 
  } 
} 

Of course, there are some important implications of how to design this class further regarding equality, immutability, etc., especially if you plan to use instances as keys for hashing.