I would suggest to use [`LocalDate`](https://docs.oracle.com/javase/8/docs/api/java/time/LocalDate.html) instead of [`String`](https://docs.oracle.com/javase/8/docs/api/java/lang/String.html) in the [Baffling Birthdays](https://exercism.org/tracks/java/exercises/baffling-birthdays) ([link](https://github.com/exercism/java/blob/9a9ff665f7513402e51eed9817020f1bb472f9fd/exercises/practice/baffling-birthdays/src/main/java/BafflingBirthdays.java) to the source) as it is more appropriate. Also, on the c sharp [tracks](https://github.com/exercism/csharp/blob/f7736850945f594606f80c027d0e5cf81ec7d6b4/exercises/practice/baffling-birthdays/BafflingBirthdays.cs) (which I believe is the first implementation of the exercise) the problem is modeled with a similar class [`DateOnly`](https://learn.microsoft.com/it-it/dotnet/api/system.dateonly?view=net-8.0).
