Classes in higher layers can extend or wrap classes in lower ones, but not the other way around. However, they can register themselves as event listeners with classes in lower levels through a generic ...

In JPA, you define your persistence rules in the realm of Java code ... the Musician class should be stored. In JPA, the primary key is the field used to uniquely identify each object in the ...

Get an overview of design patterns, then use what you've learned to evaluate whether the Composite pattern is a good choice for a particular Java ... the classes and interacting objects used ...