Dependencies is a simple library for handling arbitrary dependency graphs and invalidation. It consists of two interfaces and two abstract implementations.
Dependent is an interface that is to be implemented by any class that depends on other classes. It has one method, invalidate(), which is called whenever any of the classes that it depends on has changed. If a dependent is also a dependency, invalidate must also call invalidate on all other dependents that depend on it.
Dependency is an interface that is to be implemented by any class that other classes depend on. It has one method, invalidateDependents(), that should call invalidate() on all of its dependents. It also has a variety of methods used for adding, removing and checking for the presence of dependents. It should not usually be implemented on its own, and instead the two abstract classes should be extended instead.
AbstractDependency is an abstract implementation of Dependency that contains a logger and a set of dependencies. It provides an implementation for all methods of Dependency, but is abstract due to being intended to be extended. Methods for adding dependents check for cyclic dependencies, but only for dependents that also implement dependency.
DependencyDependent is an abstract extension of AbstractDependency that also implements Dependent. It provides a new abstract method, onInvalidate() which has the same functionality as Dependent.invalidate(), but is separate since the class also implements invalidate() with code that first calls onInvalidate() and then invalidateDependents(). Overriding invalidate() is not recommended because then the user would need to call super.invalidate() or invalidateDependents() manually, which is the reasoning for the separate onInvalidate() method.