How do you choose the right level of granularity for your Java modules?

1 Define your module boundaries

The first step to choose the right level of granularity for your Java modules is to define your module boundaries. A module boundary is the interface that exposes the functionality of a module to other modules, and hides the implementation details. A good module boundary should follow the principles of high cohesion and low coupling. High cohesion means that a module should have a clear and single responsibility, and that its elements should be closely related and work together to achieve that responsibility. Low coupling means that a module should have minimal dependencies on other modules, and that its interface should be stable and abstract. By following these principles, you can ensure that your modules are easy to understand, reuse, and change.

2 Apply the single responsibility principle

The single responsibility principle (SRP) is a software design principle that states that every module or class should have one and only one reason to change. This means that a module or class should have a single, well-defined, and coherent purpose, and that it should not perform multiple unrelated tasks. Applying the SRP can help you choose the right level of granularity for your Java modules, because it can help you avoid creating modules that are too large, too complex, or too vague. A good way to apply the SRP is to use the nouns and verbs in your domain language to identify the responsibilities of your modules. For example, if you are developing a banking system, you might have modules such as Account, Transaction, Customer, or Report.

3 Use the common closure principle

The common closure principle (CCP) is a software design principle that states that classes or modules that change for the same reasons should be grouped together, and that classes or modules that change for different reasons should be separated. This means that a module should encapsulate the changes that are likely to occur in the future, and that it should not depend on other modules that change for different reasons. Using the CCP can help you choose the right level of granularity for your Java modules, because it can help you minimize the impact of changes on your system, and improve its maintainability and testability. A good way to use the CCP is to analyze the sources of change in your system, such as user requirements, business rules, or external dependencies, and group your modules accordingly.

4 Consider the module size

When determining the optimal size of your Java modules, there is no one-size-fits-all answer as it depends on multiple factors, such as complexity, readability, reusability, and testability. To ensure you choose the right module size, avoid creating modules that are too small or too large. Too small modules can increase the overhead of managing and integrating them, while too large modules can reduce cohesion and increase coupling. Aim for modules that are consistent and proportional in size for improved readability and understandability. Additionally, use metrics and tools to measure and compare your module size. Metrics like lines of code, number of classes, methods, or dependencies can help you quantify the size of your modules. Meanwhile, code analyzers, visualizers, or refactoring tools can help you identify and improve your module size.

5 Refine your module design

The final step to choose the right level of granularity for your Java modules is to refine your module design. This means reviewing, evaluating, and improving your module design based on feedback, testing, and experience. This can help you achieve a balance between modularity and simplicity and make sure your modules meet functional and non-functional requirements. To refine your module design, you can use code reviews and peer feedback to identify and fix errors or inconsistencies. Testing and debugging tools can also be used to verify performance and reliability. Moreover, refactoring and restructuring techniques can help modify and evolve your module design without changing its behavior.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?