Users of the _value-based classes_ provided by the standard libraries—notably including users of the primitive wrapper classes—should avoid relying on the identity of class instances. Programmers are strongly discouraged from calling the wrapper class constructors, which are now deprecated for removal. New `javac` warnings discourage synchronization on value-based class instances. Runtime warnings about synchronization can also be activated, using command-line option `-XX:DiagnoseSyncOnValueBasedClasses`.

For further details, see [JEP 390](https://openjdk.java.net/jeps/390).