Hire by Technology
SERVICES
Contents
Share this article
Key Takeaways
Professional software engineers are, by definition, well-equipped to handle a variety of software projects. Abiding by software design principles is one of the many ways in which these engineers ultimately optimize the development process.
Naturally, there are several different design principles that complement your specific needs, such as when your financial software development company is building a regulated product, but there are a few software design principles that every expert developer has hard-wired into their brains.
These principles stand out because they remain dependable, time and time again.
At Trio, our senior fintech developers apply these principles every day to deliver robust, high-performance systems for clients across industries.
Let's look at some of the most valuable software design principles driving successful software development.
If you are ready to start your own project in the financial software development industry, we have the developers you need, with guaranteed production experience.
Let's first ensure that you understand what software design principles actually are and why they matter.
Software design principles are a collection of time-tested guidelines that help developers create systems that are clean, maintainable, and easy to scale.
They provide a shared language for thinking about how to organize code, structure functionality, and manage change across the software life cycle.
In practice, these principles reduce complexity by encouraging good habits such as minimizing redundancy, simplifying logic, and separating responsibilities, and in doing so, they support teamwork by making code more readable and predictable, no matter who wrote it.
Essentially, design principles act as the foundation for quality software engineering. So, by following them, developers can build systems that evolve gracefully rather than degrade over time.
In fintech and other regulated domains, disciplined design principles are what keep high-stakes, audited systems reliable and safe to change as requirements evolve, which is why our fintech engineering teams treat them as non-negotiable.
The DRY principle basically aims to reduce repetition in software programming. In doing this, the hope is that you can avoid redundancy.
It's far too common for software engineers to have to write similar pieces of code over and over again.
Thankfully, the solution to this is quite simple. For example, object-oriented programming relies on classes to save bits of data into manipulable objects.
These objects can be called at any point in time and take on parameters that describe what the object works with or the extent of the object's function.
Encapsulating code into objects depends on several other guiding principles, such as:
Abstraction refers to consolidating the complexity of a program element by hiding its internal details.
The code that exists in an object, for instance, is hidden from the user after its creation.
While working with data structures in Python, users can edit lists via Python objects.
To append an item, they would use: [list name].append(x)
Or to remove an item, they'd use: [list name].remove(x)
In these examples, append() and remove() are object calls, and x defines which list item the object should append or remove.
This is particularly great because it means the Python user needs no prior understanding of the objects' code to use these objects. They only need to name its attributes (parameters).
Another modern example of DRY in practice would be Django Packages, a directory of apps and other resources built by Django contributors and available to all Django users.
Ironically, a violation of the DRY principle is dubbed WET, or 'waste everyone's time.' AHA stands for 'avoid hasty abstractions', which leads to premature optimization.
YAGNI asserts that programmers should only add functionality when absolutely necessary and never before.
The man behind this principle, Ron Jeffries, is also a co-founder of Extreme Programming (XP), a software development methodology and Agile framework.
The original words of Jeffries were, "Always implement things when you actually need them, never when you just foresee that you need them."
Without a doubt, this should be a priority in a software methodology that will have frequent releases on the basis of changing customer requirements.
YAGNI borrows from the XP principle DTSTTCPW, or 'do the simplest thing that could possibly work.' Continuous integration plays into it as well.
Continuous integration (CI) is a software development practice where developers regularly merge code changes into a shared repository.
In a CI environment, simplicity matters, because the smaller and more focused each change is, the less risk of integration conflicts and regressions.
It goes without saying that major changes can result in disorganization down the line.
The KISS principle reminds developers that simplicity is a strength. It mirrors YAGNI pretty closely, stating that programmers should keep each small piece of software as simple as possible and avoid unnecessary complexity.
In other words, clarity beats cleverness.
Implementations of this principle are far-reaching. As early as 1960, the U.S. Navy propagated the principle to emphasize that systems work best if they are simple rather than complex.
In fact, evidence traces the origins of the principle to Kelly Johnson, a lead engineer at the Lockheed Skunk Works, an aerospace technology corporation that frequently works with the U.S. military.
Other variations of KISS include 'Keep it short and simple' or 'Keep it simple and straightforward.'
The message remains the same: complexity increases the likelihood of failure, so the simpler the design, the easier it is to understand, maintain, and extend.
As far as both YAGNI and KISS are concerned, there are a few software development strategies you can use to ensure simplicity, like loose coupling and cohesion.
Loose coupling is software development's answer to tight coupling when program structures are so densely entangled that changes become difficult and time-consuming. Developers program software with room for modularity in return for interconnectivity.
As a result, an application's features and functions operate independently and don't malfunction when another application feature or function is compromised.
Cohesion might seem like the opposite of that sentiment, but low coupling and high cohesion actually work in tandem and make for good software design.
High cohesion entails that everything in the module or class ties together and supports its central purpose.
One software concept that illustrates both high cohesion and loose coupling is microservices.
Microservices consist of numerous services, each representing a single function or feature, that are bound together via APIs.
Services within this architecture should be highly cohesive so as to be independently functional and self-contained, but the coupling between services is low.
SOLID principles are a combination of other software design principles, wrapped up in one aesthetically pleasing acronym.
Together, they form the cornerstone of object-oriented programming (OOP) and serve as a practical guide for building modular, maintainable software systems.
Classes define the behavior and data of objects, so developers can instantiate or call objects later in the program using a predefined class.
However, SRP maintains that a class should have one and only one reason to change.
All this means is that a class should not have more than one responsibility.
By isolating responsibilities, you reduce the chance that one small change will cause unintended side effects elsewhere in the system.
OCP stresses that software entities should be open for extension but closed for modification.
Basically, this specifies that adding new functionality should occur by extending existing functions, making the software development life cycle much more efficient.
Following OCP allows your development teams to build upon stable, tested code instead of rewriting it, minimizing regression risk and improving agility.
The Liskov Substitution Principle holds that an object and its sub-object must be interchangeable without disrupting the program.
More simply put, every square is a rectangle, but not every rectangle is a square.
Apply this to software development, and you'll find that giving every square object the properties of the rectangle class won't make for the most accurate geometry.
Maintaining this relationship ensures consistency and prevents unexpected behavior when working with inheritance hierarchies.
The ISP is similar to the SRP in that it aims to mitigate the negative impact of frequent changes, but it does this by urging developers to split code into multiple, independent parts.
In particular, the principle states that many client-specific interfaces are better than one general-purpose interface.
Again, microservice vs. monolithic architecture models why this is true.
Our fintech developers favor microservices over monolithic architecture because, although the latter is general-purpose, it necessitates excessive dependencies that further complicate the program.
Smaller, purpose-built interfaces make systems easier to understand, test, and evolve, reducing ripple effects when changes occur.
The Dependency Inversion Principle makes multiple assertions:
In this case, the principle emphasizes the importance of abstractions to induce low coupling.
In plain English, the principle suggests reducing dependencies by disentangling modules and abstracting details where you can, decoupling code components, and allowing independent updates and easier testing. This is a critical trait of robust architectures.
While DRY, YAGNI, KISS, and SOLID cover the foundation, experienced developers tend to keep a few other principles in their mental toolkit to fill in the gaps, especially when codebases grow or teams expand.
Each one circles back to the same goals: clarity, maintainability, and long-term stability.
It's often tempting to use inheritance because it looks neat in diagrams, but it rarely stays neat for long.
Inheritance chains can lock you into rigid structures that are hard to change without breaking something else.
Composition, on the other hand, is more flexible. You build features by combining smaller, self-contained parts instead of extending a long family tree of classes.
A lot of modern frameworks encourage this naturally.
In React, for instance, you build reusable components and piece them together, not subclass them. That approach may feel less formal at first, but it tends to survive growth and refactoring better than deep inheritance hierarchies.
Composition makes software easier to evolve and lets you swap or modify parts without rewriting everything around them. It's not always the right answer, but in most cases, it keeps complexity where it belongs, local and predictable.
The idea here is that each part of your program should handle one job and handle it well. Mixing too many responsibilities into a single place almost always leads to confusion later.
You can see this principle at work in the Model–View–Controller (MVC) pattern, where data, logic, and presentation each live in their own space. It's not perfect, but it demonstrates the value of clear boundaries.
When each layer has a clear role, you can adjust one without disturbing the others.
Objects shouldn't reach too far. The Law of Demeter says that an object should only talk to its direct neighbors, not their neighbors' neighbors.
In practice, that means avoiding long call chains like user.profile.address.city. Every extra link in that chain makes your code more fragile. If one piece changes shape, everything upstream breaks.
By keeping interactions close and deliberate, you reduce hidden dependencies and make the code easier to reason about.
Good code should do what people expect it to do. The Principle of Least Astonishment (POLA) applies to naming, behavior, and even user experience.
If a method is called deleteUser(), it should actually delete the user, not archive them or flip a flag somewhere. When code behaves in ways that surprise developers, bugs are almost guaranteed to follow.
POLA often comes down to thinking about how someone else, or your future self, will read and use the code. Predictable behavior makes systems easier to trust and much easier to maintain.
Applying design principles well is rarely as straightforward as it sounds. A principle that seems perfectly clear in theory can twist in practice, especially under pressure or when working in large, fast-moving teams.
One common trap is abstraction for its own sake.
A pattern or utility that seems clever in week one may turn into a maintenance headache by month six. You might end up designing frameworks inside frameworks, all to avoid writing the same five lines twice.
It's usually wiser to repeat yourself once or twice, then refactor later if a clear pattern emerges.
DRY, in particular, is often misunderstood. People sometimes stretch it so far that clarity gets lost.
A single shared function buried in a utilities folder may look efficient, but if no one remembers what it does or where it lives, the cost outweighs the benefit.
Inheritance is another point of friction. It's tempting to lean on class hierarchies because they look clean on paper, yet they tend to lock you into rigid structures.
Composition, or assembling behavior from smaller pieces, usually works better. It's easier to test, simpler to replace, and less likely to surprise the next person who reads your code.
Overengineering is the quieter cousin of over-abstraction. You see it in the "just in case" features: the unfinished analytics dashboard, the placeholder API endpoints, the empty caching layer. They're built with good intentions, but most never pay off.
Sticking to YAGNI keeps teams honest about what actually delivers value right now.
Simplicity can go too far as well. KISS doesn't mean flatten every idea into a one-liner. Code that's overly clever or condensed may look neat, but it often reads like a puzzle. A few extra lines written clearly are worth far more than an unreadable trick.
And finally, it's easy to treat these ideas as rules instead of reminders. SOLID, DRY, and YAGNI are meant to guide your thinking, not to police it. Real-world systems are messy, and sometimes trade-offs are unavoidable.
What matters is staying thoughtful about why you're choosing one approach over another.
The design principles you've seen here are instrumental to every programming endeavor. Make sure that these principles guide your next software project.
And if you need human resources as well, you're in luck. Trio has the key to qualified software engineers who have your best interests at heart, with production experience in the unique requirements of the fintech industry.
Expertise
Subscribe to our newsletter
Related
Content
Continue Reading
