Implementors of ProvidesKey provide a key for list items, such that items that are to be treated as distinct (for example, for editing) have distinct keys.

The key must implement a coherent set of Object.equals(Object) and Object.hashCode() methods such that if objects A and B are to be treated as identical, then A.equals(B), B.equals(A), and A.hashCode() == B.hashCode(). If A and B are to be treated as unequal, then it must be the case that A.equals(B) == false and B.equals(A) == false.