Can I add a convenient function to a type without changing its source code? *Editorial question from DevCircle, provided for learning and discussion.*

Does declaring a variable as List guarantee that nobody can change the underlying collection? *Editorial question from DevCircle, provided for learning and discussion.*

Why does the compiler reject assigning null to a String variable? *Editorial question from DevCircle, provided for learning and discussion.*

I need a small object for carrying fields and comparing values. *Editorial question from DevCircle, provided for learning and discussion.*

Should I use val for a collection that may have elements added later? *Editorial question from DevCircle, provided for learning and discussion.*