Sergii Shulga

🔑 𝗠𝗮𝘀𝘁𝗲𝗿𝗶𝗻𝗴 𝗦𝗢𝗟𝗜𝗗 𝗣𝗿𝗶𝗻𝗰𝗶𝗽𝗹𝗲𝘀 𝗶𝗻 𝗦𝗼𝗳𝘁𝘄𝗮𝗿𝗲 𝗗𝗲𝘀𝗶𝗴𝗻 Writing clean, maintainable, and scalable code isn’t just about syntaxit’s about design. That’s where SOLID Principles come in. These five timeless guidelines help developers build robust applications that are easier to extend, test, and maintain. Let’s break them down with practical detail: 1️⃣ 𝗦𝗶𝗻𝗴𝗹𝗲 𝗥𝗲𝘀𝗽𝗼𝗻𝘀𝗶𝗯𝗶𝗹𝗶𝘁𝘆 𝗣𝗿𝗶𝗻𝗰𝗶𝗽𝗹𝗲 (𝗦𝗥𝗣) 👉 𝗗𝗲𝗳𝗶𝗻𝗶𝘁𝗶𝗼𝗻: A class should have only one responsibility or reason to change. 📌 𝗪𝗵𝘆 𝗶𝘁 𝗺𝗮𝘁𝘁𝗲𝗿𝘀: - Classes that do too much quickly become fragile and hard to - maintain. Changing one responsibility might accidentally break another. 🔑 𝗕𝗲𝗻𝗲𝗳𝗶𝘁: Focused classes are easier to understand, test, and reuse. 2️⃣ 𝗢𝗽𝗲𝗻-𝗖𝗹𝗼𝘀𝗲𝗱 𝗣𝗿𝗶𝗻𝗰𝗶𝗽𝗹𝗲 (𝗢𝗖𝗣) 👉 𝗗𝗲𝗳𝗶𝗻𝗶𝘁𝗶𝗼𝗻: Classes should be open for extension, closed for modification. 📌 𝗪𝗵𝘆 𝗶𝘁 𝗺𝗮𝘁𝘁𝗲𝗿𝘀: - Keeps existing code stable while allowing new features to be added. - Prevents bugs from creeping in when requirements change. 🔑 𝗕𝗲𝗻𝗲𝗳𝗶𝘁: Future-proof code that supports growth without breaking existing features. 3️⃣ 𝗟𝗶𝘀𝗸𝗼𝘃 𝗦𝘂𝗯𝘀𝘁𝗶𝘁𝘂𝘁𝗶𝗼𝗻 𝗣𝗿𝗶𝗻𝗰𝗶𝗽𝗹𝗲 (𝗟𝗦𝗣) 👉 𝗗𝗲𝗳𝗶𝗻𝗶𝘁𝗶𝗼𝗻: Subclasses should replace their base classes without breaking the application. 📌 𝗪𝗵𝘆 𝗶𝘁 𝗺𝗮𝘁𝘁𝗲𝗿𝘀: Violations lead to unexpected behavior and broken inheritance chains. Ensures your abstractions actually behave as promised. 🔑 𝗕𝗲𝗻𝗲𝗳𝗶𝘁: Reliable and consistent code with true polymorphism. 4️⃣ 𝗜𝗻𝘁𝗲𝗿𝗳𝗮𝗰𝗲 𝗦𝗲𝗴𝗿𝗲𝗴𝗮𝘁𝗶𝗼𝗻 𝗣𝗿𝗶𝗻𝗰𝗶𝗽𝗹𝗲 (𝗜𝗦𝗣) 👉 𝗗𝗲𝗳𝗶𝗻𝗶𝘁𝗶𝗼𝗻: No client should be forced to depend on methods it does not use. 📌 𝗪𝗵𝘆 𝗶𝘁 𝗺𝗮𝘁𝘁𝗲𝗿𝘀: - Large interfaces become “fat” and force implementing classes to provide dummy methods. - Leads to unnecessary coupling. 🔑 𝗕𝗲𝗻𝗲𝗳𝗶𝘁: Flexible contracts that encourage clean, modular design. 5️⃣ 𝗗𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝗰𝘆 𝗜𝗻𝘃𝗲𝗿𝘀𝗶𝗼𝗻 𝗣𝗿𝗶𝗻𝗰𝗶𝗽𝗹𝗲 (𝗗𝗜𝗣) 👉 𝗗𝗲𝗳𝗶𝗻𝗶𝘁𝗶𝗼𝗻: Depend on abstractions, not concrete implementations. 📌 𝗪𝗵𝘆 𝗶𝘁 𝗺𝗮𝘁𝘁𝗲𝗿𝘀: - High-level modules shouldn’t be tied to low-level implementation details. - Makes code easier to test, mock, and extend. 🔑 𝗕𝗲𝗻𝗲𝗳𝗶𝘁: Enhances testability, reduces coupling, and increases flexibility. 💡 Next time you write a class, ask yourself: Am I following SOLID? 👉 Follow me Kanaiya Katarmal, and hit the 🔔 on my profile so you don’t miss upcoming .NET tips and deep dives. 𝗧𝗵𝗮𝗻𝗸𝘀 𝗳𝗼𝗿 𝗿𝗲𝗮𝗱𝗶𝗻𝗴 𝗹𝗲𝘁’𝘀 𝗰𝗼𝗻𝘁𝗶𝗻𝘂𝗲 𝗴𝗿𝗼𝘄𝗶𝗻𝗴 𝗮𝗻𝗱 𝗹𝗲𝗮𝗿𝗻𝗶𝗻𝗴 .𝗡𝗘𝗧 𝘁𝗼𝗴𝗲𝘁𝗵𝗲𝗿! 👉 𝗦𝘂𝗯𝘀𝗰𝗿𝗶𝗯𝗲 𝘁𝗼 𝗺𝘆 𝗻𝗲𝘄𝘀𝗹𝗲𝘁𝘁𝗲𝗿: https://lnkd.in/dp7tz_3V #SoftwareEngineering #SOLIDPrinciples #CleanCode #DesignPatterns #Programming #CodeQuality #Developers #SoftwareDesign #OOP

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JetBrains just announced they're moving to a single, unified IntelliJ distribution starting with version 2025.3. No more choosing between Community and Ultimate - it's one IDE with features unlocked by subscription. Why does this matter? • Some previously paid features (Spring support, database tools) are becoming FREE • The open-source commitment remains, but with a twist • This signals bigger changes in how dev tools compete in the AI era I spent time analyzing the announcement and its implications. This isn't just about IntelliJ - it's about the future of IDEs in a world where AI assistants are changing how we write code. Full analysis here → https://lnkd.in/gBpSNWUu Curious: How many of you are using IntelliJ Community Edition today? What's your take on this change?

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From Developer to CEO Part 03: 5 to 10 years of experience Congratulations, you’re now a senior developer. But you’re not a senior just because you’ve reached 5 years of experience. You’re a senior because you’ve seen more problems— and you know how to prevent them. At this stage, you should be able to build software from A to Z. But your main focus must now shift to business impact. Not just how to code, but how to solve real business problems. Code shouldn’t be your challenge. Code should be your tool—to deliver value. For that, start asking the right questions: • What’s the real problem the customer is trying to solve? • Why does the client need this feature? • What’s the expected benefit for their business? • Is there a better solution? You’re not just a developer anymore. You should become a technical partner to your clients, not just someone who takes orders. Your new mindset: 👉 How can I maximize my customer’s success? If you follow these tips, you’ll level up faster. ⸻ After 20+ years in web development, I’m sharing what I wish I had known when I was younger. This post is a follow-up to Julien Rajerison’s post. Tomorrow, we’ll talk about developers with 10+ years of experience. ⸻ You’ve got this. I’m Toky RABESON. I’m a seasoned web developer.

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🚨 More than 70% of frontend devs struggles with this follow-up question in interview about PWAs? When asked: “How does offline access work in a PWA?” Most confidently say: “Because of Service Workers!” ✅ Correct… but do you know 👇 💡 “What’s the difference between Service Workers and Web Workers?” This is where many candidates struggle but not anymore Here’s the breakdown you should never forget: ⚡ Web Workers 1️⃣ Run JS in a separate thread → avoid blocking the UI. 2️⃣ Die when the page closes. 3️⃣ Best for CPU-heavy tasks (e.g. image processing, data crunching). 🌐 Service Workers 1️⃣ Act as a proxy between your app & the network. 2️⃣ Can intercept requests, cache responses, & serve content offline. 3️⃣ Live beyond page lifecycle → even when the app is closed. 4️⃣ Backbone of offline PWAs, push notifications, & background sync. 🚀 Key takeaway: Web Workers = Performance Service Workers = Offline + Background capabilities 📌 Have you ever faced this question in your system design interview? #Frontend #Interview #frontendinterview #PWA #SystemDesign #WebWorkers #ServiceWorkers #javascript #reactjs #frontendgeek

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Flaky tests feel random. They’re not. The patterns are clear: * Timing issues (async workflows, race conditions) * Shared state (bad test isolation, order dependencies) * Environment drift (things that work locally but fail in CI) By definition, though, they’re not obvious to spot. A missing await, an unseeded random number, a fragile assertion. These problems tend to show up after the developer who wrote them has moved on to the next thing, reducing the likelihood that anyone will take time to fix them. AI is going to multiply these issues. It’s *also* going to help us catch them faster. The challenge for leaders: don’t accept flaky tests as inevitable. They’re just tech debt we’ve been too slow to pay down.

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Waiting half an hour for your tests to finish? That’s not feedback - that’s punishment 🧪 You might have been there: Every new integration test adds another minute to your overall build time. Twenty minutes turn to thirty. CI times explode. Developers stop writing integration tests and become unhappy. Flaky tests appear. Bugs slip through. Releases slow down. But what if you could slash that time, without deleting a single test? With Spring Test, that's possible. It's a hidden gem called Spring TestContext Context Caching 🏆 So, how do you know how many contexts are spinning up? More importantly, how do you figure out why they aren’t being reused? That’s why I built Spring Test Profiler ⏱️ Meet Spring Test Profiler - the free, open-source x-ray for your test suite. Integration is as simple as this three-step process: 1. Add the dependency (Maven/Gradle snippets appear on screen). 2. Run your tests. 3. Open the report at: target/spring-test-profiler/report.html. Within the report, you’ll see: • How many contexts started, and why. • Which tests are sharing configs versus starting their own. • Exact diffs: profiles, properties, or annotations blocking cache reuse. The overall goal is to help identify cache misses and align your tests to reuse contexts for faster feedback 🚤 Spring Test Profiler: Profile. Optimize. Deliver. Try it yourself: https://lnkd.in/djXVJiNE Below is a demo of a section in the report to analyze and compare two contexts 🆚

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Most engineers get stumped by high-level design in system design interviews. Often, they aren't even sure where to begin. Luckily, we've put together a tried and tested framework for easily building up to a working application. 1) Identify "what the system should do" 🔶 These are also known as the functional requirements 🔶 E.g. The users can make posts, like posts, follow other users etc 💡Think about what features you would want the system to have 2) Identify "how the system should behave" under specific constraints 🔶 What are the latency requirements? 🔶 How do we ensure our servers don't crash with an increasing number of users? 🔶 How do we ensure the system is always available when it's expected to be available? 🔶 How do we ensure fault tolerance to prevent data loss? 🔶 What are the trade-offs? Why should we choose one technique over the other? 3) Start addressing functional requirements in the most basic way possible 🔶 Map the data flow for each requirement with some services. E.g. When the client makes a post, they interact with a "Tweet Service" and that gets stored in a "Tweet DB" ❌ Do not add any complicated parts - this way the interviewer can correct you early on if you've made a mistake. 4) Think about how you can use your knowledge of the core system design components when addressing the functional requirements 🔶 If we have multiple services, it probably makes sense to use an API Gateway. Think of it, you wouldn't want to expose the services directly to clients. Instead, you want controlled access. 5) Once you have a feasible "what" down, address the non-functional requirements ❌ Biggest mistake candidates make here is to not tie the recommendations back to the original non-functional requirements they identified. Think about: 🔶 How you would choose between vertical scaling and horizontal scaling, and why? In our case, we can deploy more instances of the same service so we can handle requests in parallel. 🔶 Hmm... but how would you decide traffic is distributed evenly across all instances? Maybe we should consider a load balancer. 🔶 For latency, would the system benefit from caching? Is it necessary? 🔶 Think about edge cases when it comes to preventing data loss - would it make sense to have a buffer? 🔶 How do we safeguard against a database going down? A distributed database is designed to replicate and store data across multiple nodes in a cluster. High-level design should take 15-20 minutes, which is the bulk of the interview. This is then followed by a deep dive session, which lasts another 10-15 minutes. We will be covering how to ace your deep dive session in the upcoming posts. Stay tuned! --- Put this framework into practice today -> https://lnkd.in/ecQeq-s6

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Systems don’t fail from missing features. They fail because the core architecture was never solid. In system design, everything depends on the foundation. Remove it, and the system collapses: - A payments platform without reliable transaction handling isn’t a platform. - A chat system without fault-tolerant real-time delivery isn’t chat. - An analytics pipeline without accurate, durable event storage isn’t analytics. Yet, teams often start at the edges, focusing on UI polish, onboarding flows, and third-party integrations, before locking in the core. Here is what I had learn: 1. Find the core Ask: If I remove this component, does the system still exist? And make it resilient. 2. Separate core from extras Core = the minimal set of services that must stay consistent and reliable. Extras = scalability add-ons, convenience APIs, or UX niceties. 3. Invest in the core first - Design for correctness and durability before performance. - Keep protocols and data models simple and explicit. - Make failure handling clear and predictable. 4. Defer the extras Adding complexity before the foundation is proven is like scaling a system that doesn’t even work correctly yet. 5. Stress test the core Push it to its breaking point early. Load, failure, recovery, and consistency testing matter more than flashy features. The truth: Shiny features don’t save a weak system. A solid core: durable, reliable, and simple, does.

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'We only hire senior developers' Congrats! You're building a time bomb. Here's why: Senior-only teams create: • Echo chambers of outdated practices • Zero knowledge transfer • Expensive solutions to simple problems • 10 architects, no builders What you're really missing: • Fresh perspectives • Hunger to learn • Questions that challenge assumptions • Future leaders The brutal truth: • Your 'senior' requirements are fear-based • Your '10 years experience' is arbitrary • Your 'no junior devs' policy is expensive technical debt Why this matters: • Innovation needs new eyes • Growth requires teaching • Sustainability demands succession • AI is leveling the experience gap anyway How to fix it: 1. Hire for potential, not just experience 2. Create mentorship structures 3. Balance your team pyramid 4. Accept that juniors today code better than seniors did 5 years ago Remember: Today's 'risky' junior is tomorrow's 'savior'. What's your take on the senior-only trend? Drop your thoughts below 👇 *** P.S. If your entire team is senior developers, who's asking the 'stupid' questions that prevent stupid mistakes?

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