Question

As a C++ oldtimer I have managed to solve my problem but I can not wrap my head around the underlying Java mechanisms here:

Vector<Object> x = new Vector<Object>();        // OK
ArrayList<Object> y = new ArrayList<Object>();  // OK
List<Object> zzz = new ArrayList<Object>();     // OK solves problem below but question remains
List<Object> z = new List<Object>();            // WHY? Compiler error: Cannot instantiate 

Answer 1

List is an interface, somewhat like a class with some = 0 methods in C++. You can’t instantiate it.

But ArrayList<T> “inherits” List<T> (or in Java terms, implements it), so those references are assignment-compatible.