Even without multithreading, mutating the value of a key (such that hashCode() changes) after putting it in the map entry won't return the same entry. This is a

Even without multithreading, mutating the value of a key (such that hashCode() changes) after putting it in the map entry won't return the same entry. This is a HashMap basic, not just something special jujitsu you need to learn with multithreading. I think blaming someone for using a non-thread-safe data structure without sufficient explicit locking is justifiable.