A repository of "shared secrets", which are a mechanism for calling implementation-private methods in another package without using reflection. A package-private class implements a public interface and provides the ability to call package-private methods within that package; the object implementing that interface is provided through a third package to which access is restricted. This framework avoids the primary disadvantage of using reflection for this purpose, namely the loss of compile-time checking.

Usage of these APIs often means bad encapsulation designs, increased complexity and lack of sustainability. Use this only as a last resort!