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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 = ... 
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A Pair is a Tuple from JavaTuples library that deals with 2 elements. Since this Pair is a generic class, it can hold any type of value in it. Since Pair is a Tuple, hence it also has all the characteristics of JavaTuples: They are Typesafe. They are Immutable.
Technically that should be a Tuple2 , as it is a container for two heterogeneous items. Scala has tuple classes that hold anywhere between two and twenty-two items, and they're named Tuple2 through Tuple22 . To do the same thing in Java you would just implement the same pattern for Tuple2 through Tuple22 in Java.
Note that the collection/ array must have the same type and values as the tuple. The collection/array must have the same type as the Tuple and the number of values in the collection/ array must match the Tuple class. Syntax: ClassName <type-1, type-2, …., type-n> object = ClassName.
Pairs provide a convenient way of handling simple key to value association, and are particularly useful when we want to return two values from a method. A simple implementation of a Pair is available in the core Java libraries.
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.
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