Where possible, code that previously synchronized on this (or on the
class in the case of static methods) has been updated to use an
internal monitor object instead. This allows the locking model that's
employed to be an implementation detail rather than part of the
class's API.
Classes that override a synchronized method continue to declare
the overriding method as synchronized. This ensures that locking
is consistent across the superclass and its subclass.
Closes gh-6262
Ensure that Collections.isEmpty() is used to check if there are no
elements in a collections. This is more explicit and can be faster than
calling .size().
Closes gh-4783
Andy Wilkinson
Phillip Webb
Kirill Vlasov