Refactoring is the process of restructuring a code without changing or adding to its functionality and external behavior. There are a lot of ways to go about refactoring but it mostly goes towards applying standard basic actions. These changes in the existing code save the software’s functionality and behavior since the changes are so tiny, they are less likely to cause any errors. So, what is the point of refactoring? Well, refactoring is to turn any messy confusing code into a clean understandable one instead. When a code is messy it means that the code is hard to understand and maintain, when it’s time to add a required functionality it causes a lot of problems with the code because it’s confusing already. With a clean code, it’s easier to make any changes and improve on any problems. Also with a clean code anybody who ever works with the code is able to understand the code and can appreciate how organized it is. When a messy code isn’t cleaned up it can affect any feature developments because developers have to take more time to understand the code and track the code so that they can make any changes themselves.

Knowing when to refactor is important and there are different times to refactor your code. Like refactoring, while you’re reviewing the code, reviewing the code before it goes live is the best time to refactor and make any changes you can before pushing it through. You can also schedule certain parts of your day to refactor your code instead of doing it all at once. By cleaning your code you are able to catch any bugs before they create any problems in your code. The main thing about refactoring your code is that cleaning up a dirty code can reduce technical debt. Clean code is easier to read and if anybody else besides the developer works on that code they are also able to easily understand that code as well as maintain and add features to it. The less complicated the code is, it can lead to improved source-code maintenance. With a clean code, the design can be used as a tool for any other developers it can become the basis of a code elsewhere. This is why I believe that refactoring is important because changing just the smallest piece of code can lead to a better functional approach to programming. It helps developers get a better understanding of the code as well as making better design decisions.

From the blog CS@Worcester – Kaylene Noel's Blog by Kaylene Noel and used with permission of the author. All other rights reserved by the author.

This week, I wanted to continue writing about the SOLID software design principles. The next principle I have to cover is the Liskov substitution principle. This principle expands upon the Open/Closed principle I wrote about the previous week, providing a guideline on how a superclass and its child classes should behave.

This principle was first defined by Barbara Liskov in 1987, and later adopted by Robert C. Martin. From a paper that Barbara Liskov cowrote with Jeanette Wing, they defined the Liskov substitution principle as a mathematical property: “Let Φ(x) be a property provable about objects x of type T. Then Φ(y) should be true for objects y of type S where S is a subtype of T.”

Translated into plain English, this principle states that instances of a superclass in a program should be able to be replaced by one of its subclasses without breaking the program. Overridden methods from a subclass must accept the same input as the superclass’s original method, and the return value of a subclass’s method must be able to be used the same way as the value returned by a superclass’s original method.

Creating code that abides by this principle isn’t simple, as the compiler can only verify that the structure of your code is correct, not that any specific behavior of your code always executes when desired. Creating robust test classes and cases is the best way to check if your code is following the Liskov substitution principle, checking portions of your program using all subclasses of a particular component to ensure there are no resulting errors or loss in performance.

The author of this article series has included another code example representing a coffee machine to illustrate this design principle, as they have done in their previous articles. They present the problem of creating different subclasses of coffee machines from a generic parent class, with two classes with an “addCoffee()” method that accepts two different types of objects, CoffeeBean and GroundCoffee. The author suggests two solutions, either creating a common Coffee class that can be utilized by both the BasicCoffeeMachine class and the PremiumCoffeeMachine class, or create a common implementation of a “brewCoffee()” method that also appears in both CoffeeMachine classes. The first solution would violate the Liskov substitution principle, because each CoffeeMachine class would need to validate that they are receiving the correct input type for the addCoffee() method, as the BasicCoffeeMachine class can only use the GroundCoffee type, and not the CoffeeBean type. The author’s preferred solution is to remove the addCoffee() method from both CoffeeMachine classes and implement a common brewCoffee() method in the CoffeeMachine interface implemented by BasicCoffeeMachine and PremiumCoffeeMachine. Since all CoffeeMachines are expected to brew filtered coffee grounds, this brewCoffee() method should have that responsibility.

I want to further understand this principle because in a past project, I made a simple video game that used lots of objects of different subtypes that inherited from a single GameObject parent class. If I want to return to that project, or begin a similar one in the future, I want to make sure that I am not losing any functionality as I design and implement subclasses of a broader parent class.

From the blog CS@Worcester – Michael's Programming Blog by mikesprogrammingblog and used with permission of the author. All other rights reserved by the author.

SOLID Design Principles

SOLID is a subcategory of five principles, the first being:

Single Responsibility Principle (SRP)

SRP states that a class, module, or function should only have a singular function.

For example, having a class ‘Animal’ with methods ‘displayAnimalName()’, ‘animalSound()’, ‘feedAnimal()’ would be a violation of SRP because each method has a different function. Creating three separate classes that would each represent a functionality resolves the violation. This entails new classes are created for DisplayName, Sound, and Feeding. Although this may lead to more code overall, having separate classes allows for better maintainability. Without SRP, making changes to one functionality may break another.

Open-Closed Principle (OCP)

OCP states that code should be open for extension, but closed for modification. Therefore the code’s behavior should be extended by adding more code rather than modifying the existing code.

Function ‘getArea()’ calculates the area of a shape using a switch statement where there are cases for a square and circle. To add another shape, the switch statement must be modified to add a case for the new shape, violating OCP. To satisfy OCP, one would create separate classes for each shape that implements the Area interface. Now to add a new shape, one would add a new class and implement the Area interface rather than modify the original switch statement.

Liskov Substitution Principle (LSP)

LSP states that child class objects must be substitutable with objects of the parent class without affecting the correctness of the code.

Imagine a parent class ‘Bird’ with method ‘fly()’, and child classes ‘Penguin’ and ‘Eagle’. Both inherit ‘fly()’ because ‘Penguin’ and ‘Eagle’ are child classes of ‘Bird’. Because penguins cannot fly, the ‘fly()’ method in ‘Penguin’ has been overridden to do nothing. Doing this would violate LSP because objects of ‘Penguin’ would not be substitutable for objects of ‘Bird’.

Interface Segregation Principle (ISP)

ISP states that users should not be forced to implement interfaces they will not use.

Imagine an interface ‘Worker’ that has methods ‘work()’ and ‘eatOfficeLunch()’. Classes ‘FieldWorker’ and ‘OfficeWorker’ both implement the ‘Worker’ interface. Because ‘FieldWorker’ does not eat in office, the method ‘eatOfficeLunch()’ is unnecessary. This violates ISP because ‘FieldWorker’ is forced to implement ‘eatOfficeLunch()’ although the method will not be used.

Dependency Inversion Principle (DIP)

DIP states that high-level modules should not depend on low-level modules, keeping that as separate as possible.

For example, there’s a project with high-level systems (backend logic), that relies on low-level modules (database access). However the project’s team wants to change the database from one type to a different. Because the high-level systems are specifically written and depend on the database type, they would no longer work once the database type changes. Having high-level systems be more abstract and able to be implemented in different ways is ideal.

Conclusion

The article used was chosen because it gave examples with code, making understanding easy. As someone who wishes to have a career in software development, knowing the best practices for designing maintainable code is crucial. I expect to apply these principles to all future projects.

Resources:

https://www.freecodecamp.org/news/solid-design-principles-in-software-development/

From the blog CS@Worcester – Zack's CS Blog by ztram1 and used with permission of the author. All other rights reserved by the author.