A generic pair in Java
Java interview exercise on Generics & Optional, difficulty 1 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
Write record Pair<A, B>(A first, B second) with a static factory of(a, b), a method swap() returning a Pair<B, A>, and withFirst(a) returning a copy with the first element replaced (records are immutable, so every change is a new record).
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.