How do you refactor a large and complex JavaSE class to follow the single responsibility principle?

1 Identify the responsibilities

The first step is to identify the responsibilities of the class and how they are related to each other. You can use tools like code analysis, documentation, tests, or comments to help you with this task. You can also ask yourself some questions like: What does the class do? What are the inputs and outputs of its methods? What are the dependencies and collaborators of the class? What are the sources of change or variation for the class? Try to group the methods and fields of the class according to their responsibilities and label them accordingly.

2 Extract the responsibilities

The next step is to extract the responsibilities of the class into separate classes or interfaces. You can use techniques like extract method, extract class, extract interface, or extract superclass to do this. The goal is to create smaller and simpler classes that have a single responsibility and a clear interface. You can also use design patterns like strategy, decorator, or adapter to help you with this step. For example, if your class has multiple methods that implement different algorithms for the same task, you can extract them into separate classes that implement a common interface and use the strategy pattern to delegate the execution.

3 Refactor the original class

The final step is to refactor the original class to use the extracted classes or interfaces. You can use techniques like replace method with method object, replace inheritance with delegation, or replace conditional with polymorphism to do this. The goal is to reduce the complexity and coupling of the original class and increase its cohesion and readability. You can also use dependency injection or inversion of control to inject the extracted classes or interfaces into the original class and avoid hard-coding them.

By following these steps, you can refactor a large and complex JavaSE class to follow the SRP and improve its quality and maintainability. Remember that refactoring is an iterative and incremental process that requires testing and verification along the way. You can also apply the other SOLID principles to further enhance your software design.

4 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?