For the full description, implementation variations, consequences, and detailed sample, see Page 150 in Java Application Architecture.
Statement
Modules should be externally configurable.
Description
The ability to configure a module to it’s usage context increases our ability to reuse the module across contexts, whereas tightly coupling configuration to the module prohibits reuse. External configuration allows a module to be [...]
For the full description, implementation variations, consequences, and detailed sample, see Page 150 in Java Application Architecture.
Statement
Create a facade serving as a coarse-grained entry point to the modules underlying implementation.
Description
We create fine-grained and lightweight modules to increase module reuse. Unfortunately, fine-grained modules can also be difficult to use because the user must understand the API [...]
For the full description, implementation variations, consequences, and detailed sample, see Page 150 in Java Application Architecture.
Statement
Exceptions should be close to the class or interface that throw them.
Description
Sadly, dealing with exceptions in enterprise software systems is often an afterthought. But allocation of exceptions to modules has significant implications on the modularity, and more specifically the [...]
For the full description, implementation variations, consequences, and detailed sample, see Page 150 in Java Application Architecture.
Statement
Modules should be independent of the runtime container.
Description
Modules with excessive runtime container dependencies are heavyweight modules that cannot execute outside the confines of the runtime container. Lightweight modules with no container dependencies have significant advantages.
For the full description, implementation variations, consequences, and detailed sample, see Page 150 in Java Application Architecture.
Statement
Module relationships should be levelized.
Description
Levelized modules demand that module relationships be acyclic. Any cycles in module relationships therefore prevents levelization. To levelize modules relationships, there are several steps.
For the full description, implementation variations, consequences, and detailed sample, see Page 150 in Java Application Architecture.
Statement
Module behavior should serve a singular purpose.
Description
There are two key elements that affect module cohesion. These follow:
The rate at which the software entities within a module change.
The likelihood that the software entities within a module are reused together.
Based on [...]
For the full description, implementation variations, consequences, and detailed sample, see Page 150 in Java Application Architecture.
Statement
Use factories to create a modules implementation classes.
Description
One of the challenges we face with Abstract Modules is how the object relationships are established at runtime. A class dependent on an abstraction should avoid referencing any of the implementing classes, [...]
For the full description, implementation variations, consequences, and detailed sample, see Page 150 in Java Application Architecture.
Statement
Place abstractions and the classes that implement them in separate modules.
Description
You create an abstract class or interface to help reduce coupling between classes. This offers the ability to create new implementations of the abstraction without impacting clients dependent on [...]
For the full description, implementation variations, consequences, and detailed sample, see Page 150 in Java Application Architecture.
Statement
Depend upon the abstract elements of a module.
Description
Modules heavily depended upon have many incoming dependencies. In other words, you may have many modules that all depend on a single module. On one hand, this is a good thing because [...]
For the full description, implementation variations, consequences, and detailed sample, see Page 150 in Java Application Architecture.
Statement
Each module should have a corresponding test module.
Description
Writing tests is one of the most important activities you should perform as a developer. Create a robust suite of tests has significant advantages, both long and short term. Short term, tests [...]