Composing Objects - Java Concurrency in Practice - page 73

4.3.1. Example: Vehicle Tracker Using Delegation
As a more substantial example of delegation, let's construct a version of the vehicle tracker
that delegates to a thread-safe class. We store the locations in a Map , so we start with a thread-
safe Map implementation, ConcurrentHashMap . We also store the location using an im-
mutable Point class instead of MutablePoint , shown in Listing 4.6 .
Listing 4.6. Immutable Point class used by DelegatingVehicleTracker .
Point is thread-safe because it is immutable. Immutable values can be freely shared and
published, so we no longer need to copy the locations when returning them.