Generic pair class

Question

Just attempting this question I found in a past exam paper so that I can prepare for an upcoming Java examination.

Provide a generic class Pair for representing pair

Answer 1

The need for a Pair class usually crops up in larger projects - I'm about to (re)implement one for the current project (as previous implementations are not accessible).

Generally I make it an immutable POJO, with a convenience function to create instances. For example:

public class Pair
{
    public final T first;
    public final U second;
    public static  Pair of(T first, U second);
}

So that the end-user can write:

return Pair.of (a, b);

and

Pair p = someThing ();
doSomething (p.first);
doSomethingElse (p.second);

As mentioned above, the Pair class should also implement hashCode(), equals(), optional-but-useful toString(), as possibly clone() and compareTo() for use where these are supported by T and U - though extra work is required to describe how these contracts are supported by the Pair class.