Object-oriented systems are usually partitioned into layers of related responsibilities and only dependencies in one direction are allowed, from higher layers (more specific, less reusable) to lower ...

Reference objects aren't just useful when memory is at a premium; they can also be used to provide slick caching abilities to any application.

Get to know the Java persistence standard based on Hibernate and learn how to use JPA to store and manage Java objects in a relational or NoSQL database.