Using Pairs or 2-tuples in Java [duplicate]

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 = ...

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.

javatuples is a dedicated project for tuples in Java.

Unit<A> (1 element)
Pair<A,B> (2 elements)
Triplet<A,B,C> (3 elements)

Apache Commons provided some common java utilities including a Pair. It implements Map.Entry, Comparable and Serializable.

If you are looking for a built-in Java two-element tuple, try AbstractMap.SimpleEntry.

As an extension to @maerics nice answer, I've added a few useful methods:

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; 
    }

    @Override
    public String toString() {
        return "(" + x + "," + y + ")";
    }

    @Override
    public boolean equals(Object other) {
        if (other == this) {
            return true;
        }

        if (!(other instanceof Tuple)){
            return false;
        }

        Tuple<X,Y> other_ = (Tuple<X,Y>) other;

        // this may cause NPE if nulls are valid values for x or y. The logic may be improved to handle nulls properly, if needed.
        return other_.x.equals(this.x) && other_.y.equals(this.y);
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((x == null) ? 0 : x.hashCode());
        result = prime * result + ((y == null) ? 0 : y.hashCode());
        return result;
    }
}