How can you improve the cohesion and coupling of your software components?

1 Why cohesion and coupling matter

Cohesion and coupling matter because they influence how easy or hard it is to modify, test, debug, and reuse your software components. High cohesion and low coupling are desirable qualities that make your components more modular, independent, and understandable. Low cohesion and high coupling, on the other hand, make your components more complex, interdependent, and brittle. Therefore, improving the cohesion and coupling of your software components can help you create more robust, flexible, and maintainable software.

2 How to measure cohesion and coupling

When measuring the cohesion and coupling of your software components, various metrics can be used depending on the level of abstraction and type of analysis. Lines of code (LOC) is a simple way to estimate component cohesion by counting the number of lines. However, this metric does not account for quality or complexity of the code. Alternatively, the Lack of Cohesion in Methods (LCOM) metric compares the number of methods that share at least one attribute with those that don't, with higher LCOM indicating lower cohesion and a higher chance of splitting the component into smaller ones. Coupling between Objects (CBO) counts the number of other components a component is directly or indirectly connected to, with higher CBO indicating higher coupling and risk of ripple effects when changing the component. Efferent and afferent coupling (Ce and Ca) additionally measure how many components depend on each other, with higher Ce indicating higher coupling and lower stability, and higher Ca indicating higher coupling and popularity.

3 How to improve cohesion

One way to improve the cohesion of your software components is to apply the single responsibility principle (SRP), which states that a component should have only one reason to change. This means that a component should perform only one well-defined task and delegate other tasks to other components. For example, if you have a component that handles both user authentication and data validation, you can split it into two components: one for authentication and one for validation. This way, you can reduce the LOC and the LCOM of each component and make them more cohesive.

Another way to improve the cohesion of your software components is to use abstraction and encapsulation, which are techniques that hide the implementation details and expose only the essential functionality of a component. This way, you can reduce the complexity and increase the readability of your component. For example, if you have a component that performs a complex calculation, you can hide the algorithm and the variables inside the component and provide a simple method to access the result. This way, you can isolate the logic and the data of the component and make it more cohesive.

4 How to improve coupling

One way to improve the coupling of your software components is to apply the dependency inversion principle (DIP), which states that a component should depend on abstractions rather than on concrete implementations. This means that a component should use interfaces or abstract classes to communicate with other components, rather than relying on specific classes or objects. For example, if you have a component that uses a database to store data, you can define an interface that specifies the methods to access the data and use it as a parameter for the component. This way, you can reduce the CBO and the Ce of the component and make it more loosely coupled.

Another way to improve the coupling of your software components is to use dependency injection, which is a technique that allows a component to receive its dependencies from an external source, rather than creating or obtaining them itself. This way, you can decouple the creation and the usage of the dependencies and make your component more adaptable and testable. For example, if you have a component that needs a logger to record its activities, you can pass a logger object as an argument to the component's constructor or setter method, rather than instantiating a logger inside the component. This way, you can reduce the CBO and the Ce of the component and make it more loosely coupled.

5 How to refactor your code

Refactoring is the process of improving the design of your existing code without changing its functionality. It is a beneficial practice to apply tips and techniques to improve the cohesion and coupling of software components. However, refactoring can also introduce errors or break existing features, so it is important to adhere to best practices. These include planning your refactoring by identifying components that need improvement, goals you want to achieve, and steps you want to take. Additionally, testing your code before and after refactoring is essential to ensure functionality and quality. Finally, committing changes to a version control system like Git or SVN will enable you to keep track of modifications and revert them if needed. Tools like code review, code diff, or code documentation can help with communicating and documenting changes as well as getting feedback from others.