try-with-resources in Java
Java interview exercise on Exceptions & validation, difficulty 2 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.
Given class Connection implements AutoCloseable (it counts how many are open), write query(sql) that opens a Connection with try-with-resources, throws IllegalArgumentException when sql is blank, and otherwise returns "ok: " + sql. Whether it returns or throws, the connection must be closed afterwards.
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.