Implement sorting with Java Streams

Problem Sort a collection of objects using the Java Streams API, then extend it to multi-key ordering. Be ready to fall back to implementing a sort manually if asked.

Input / Output

• Input: a List<T> (e.g. employees) and one or more sort keys.
• Output: a new sorted list (Streams are non-mutating).

Example

• Sort employees by department ascending, then by salary descending.