How do you design and test your objects for low coupling and high cohesion?

1 What is coupling?

Coupling refers to the degree of dependency or interaction between different components of a system, such as classes, methods, or modules. High coupling means that a change in one component affects many others, making the system complex, rigid, and fragile. Low coupling means that the components are loosely connected and can function independently, making the system simple, flexible, and robust.

2 What is cohesion?

Cohesion refers to the degree of relatedness or consistency of the responsibilities or functionalities of a single component of a system, such as a class, method, or module. High cohesion means that the component does only one thing well and has a clear purpose and scope. Low cohesion means that the component does many things poorly and has a vague or overlapping role and scope.

4 How to design your objects for low coupling and high cohesion?

Designing your objects for low coupling and high cohesion requires following common design principles and patterns. These include the Single Responsibility Principle, which states that each class or method should have only one reason to change and do one thing well. The Open-Closed Principle states that each class or method should be open for extension, but closed for modification. The Liskov Substitution Principle states that each subclass or derived class should be substitutable for its superclass or base class. The Interface Segregation Principle suggests that each interface or abstract class should be small and focused and not force its clients to depend on methods or properties they don't use. The Dependency Inversion Principle states that each class or method should depend on abstractions, not concretions. Additionally, there are Factory, Strategy, and Observer patterns which are creational, behavioral, and behavioral patterns respectively. These can be interchanged at runtime and provide a common interface to create different types of objects.

5 How to test your objects for low coupling and high cohesion?

To assess the low coupling and high cohesion of your objects, you need to apply certain testing techniques and tools that measure and enhance the quality of your code. Unit testing verifies the functionality and correctness of individual units or components of your code, while mocking replaces the behavior or state of a real dependency with a dummy object that can be monitored by the test. Code coverage is a metric that measures the percentage of your code that is executed by your tests, while code smell is a term for poor design or implementation that affects the quality, readability, or maintainability of your code. Refactoring is a technique that improves the structure, design, or implementation of your code without changing its functionality or behavior. This technique helps eliminate code smells, reduce complexity, and increase modularity, readability, and maintainability.

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?