An Optional chain in Java
Java interview exercise on Generics & Optional, difficulty 2 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.
Given record User(String name, String email) where email may be null, write findEmail(users, id) that returns an Optional<String> holding the user's email in lower case and trimmed, empty when the id is unknown, the email is null, or the email is blank. One chain: Optional.ofNullable, map, filter.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Progress is saved in your browser, and in your account if you sign in.