Address Book with Collections and Streams

This GitHub Classroom kata mirrors real-world work with messy CSV data. You’ll load contacts, validate rows using a custom exception, and query with Java Streams.

How to run

./gradlew test

Or compile & run a main if you add one:

javac src/main/java/com/example/addressbook/AddressBook.java
java com.example.addressbook.AddressBook

Tasks (driven by tests)

1. Load valid contacts from contacts.csv.
2. Throw a custom exception for malformed rows and log errors without crashing.
3. Search by name (partial, case-insensitive).
4. Filter by city (case-insensitive).
5. Filter by phone prefix.
6. Return unique cities (Set<String>).
7. Sort contacts by name (case-insensitive).
8. Group & count contacts by city (Map<String, Long>).

Templates are intentionally minimal so you write most of the code. Read each test to see expected behaviour and method signatures.