Anis Rahman’s Post

Design Patterns — Must Know for Interviews What are Design Patterns? - Reusable solutions to common design problems - Help in writing clean, scalable, maintainable code - Widely expected in LLD interviews --- 1 — Singleton Pattern - Ensures only one instance of a class exists - Used in logging, configuration, cache Example: class Singleton { private static Singleton instance; private Singleton() {} public static Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; } } --- 2 — Factory Pattern - Creates objects without exposing creation logic - Promotes loose coupling Example: interface Notification { void notifyUser(); } class EmailNotification implements Notification { public void notifyUser() {} } class NotificationFactory { public static Notification create(String type) { if (type.equals("EMAIL")) return new EmailNotification(); return null; } } --- 3 — Strategy Pattern - Allows selecting behavior at runtime - Encapsulates algorithms Example: interface PaymentStrategy { void pay(); } class UpiPayment implements PaymentStrategy { public void pay() {} } --- 4 — Observer Pattern - One-to-many dependency - When one object changes, others are notified Example: interface Observer { void update(); } --- When to Use These in Interviews - Singleton → Shared resources (Config, Logger) - Factory → Object creation logic - Strategy → Multiple behaviors (Payment, Sorting) - Observer → Event systems (Notifications, Subscriptions) Common Mistakes - Using patterns unnecessarily - Over-complicating simple designs - Not explaining “why” you chose a pattern Action - Take a problem (e.g., Payment System) - Apply at least 2 design patterns - Focus on clarity, not complexity #LLD #DesignPatterns #SystemDesign #SDE #Java #CodingInterview #100DaysOfCode

Everyone says they know **Singleton Design Pattern**… But in interviews? That’s where reality hits 💀 Let’s break the *actual grilling* (SDE → Architect level) 👇 --- ### 🔥 Q1: Why not just use a static class? 👉 Because static ≠ flexible ✔ No lazy initialization ✔ No interface/extension support **Real Answer:** Singleton gives controlled instantiation + OOP flexibility. Static is just utility… not design. --- ### 🔥 Q2: Is your Singleton thread-safe? 👉 If you wrote basic code → NO ❌ **Real Answer:** We ensure thread safety using: * Double-checked locking (`volatile`) * Synchronized block * Or best → Enum Singleton **Key Insight:** Thread safety is not default… you design it. --- ### 🔥 Q3: Can Singleton break? 👉 YES. And most devs don’t know this. It can break via: * Reflection * Serialization * Cloning **Real Answer:** We secure it using constructor checks, `readResolve()`, disabling cloning… Or simply → use Enum. --- ### 🔥 Q4: Why Enum Singleton is best? 👉 Because JVM handles everything for you ✔ Thread-safe ✔ Reflection-safe ✔ Serialization-safe **Architect Line:** Don’t fight JVM… leverage it. --- ### 🔥 Q5: When NOT to use Singleton? 👉 This is where seniors stand out. Avoid when: * It creates global state * Hard to test * Future needs multiple instances **Reality:** Overuse of Singleton = design smell 🚨 --- ### 🔥 Q6: Real-world usage? * Logger * Config Manager * Cache * Thread Pool 👉 One system → One shared brain --- ### 🔥 Q7: What about Spring Boot? 👉 Plot twist 🔥 Spring beans are Singleton by default… But managed by IoC container. **Key Line:** Spring Singleton ≠ JVM Singleton It’s per container, not truly global. --- ### 🎯 Final Punch Singleton is easy to write… But **hard to design correctly in production**. Most devs stop at: 👉 “One class, one object” Real engineers think: 👉 Thread safety 👉 Security 👉 Scalability 👉 Testability --- If you can answer all these in an interview… You’re not a fresher anymore ⚡ #Java #SystemDesign #LowLevelDesign #Backend #SpringBoot #SoftwareEngineering

🚀 𝐋𝐋𝐃 𝐒𝐞𝐫𝐢𝐞𝐬: 𝐂𝐫𝐞𝐚𝐭𝐢𝐨𝐧𝐚𝐥 𝐃𝐞𝐬𝐢𝐠𝐧 𝐏𝐚𝐭𝐭𝐞𝐫𝐧𝐬 Over the past few days, I’ve been breaking down core creational design patterns in the simplest way possible — with clear Java examples and real-world use cases. If you’re preparing for backend roles or system design interviews, these are must-know concepts. Here’s the complete list: 🔹 𝐋𝐋𝐃 #𝟏: 𝐅𝐚𝐜𝐭𝐨𝐫𝐲 𝐃𝐞𝐬𝐢𝐠𝐧 𝐏𝐚𝐭𝐭𝐞𝐫𝐧 https://lnkd.in/gEvYbeNQ 🔹 𝐋𝐋𝐃 #𝟐: 𝐀𝐛𝐬𝐭𝐫𝐚𝐜𝐭 𝐅𝐚𝐜𝐭𝐨𝐫𝐲 𝐏𝐚𝐭𝐭𝐞𝐫𝐧 https://lnkd.in/gMCDEZUN 🔹 𝐋𝐋𝐃 #𝟑: 𝐒𝐢𝐧𝐠𝐥𝐞𝐭𝐨𝐧 𝐏𝐚𝐭𝐭𝐞𝐫𝐧 https://lnkd.in/gAzNNxEY 🔹 𝐋𝐋𝐃 #𝟒: 𝐁𝐮𝐢𝐥𝐝𝐞𝐫 𝐏𝐚𝐭𝐭𝐞𝐫𝐧 https://lnkd.in/gcEwS55R 🔹 𝐋𝐋𝐃 #𝟓: 𝐏𝐫𝐨𝐭𝐨𝐭𝐲𝐩𝐞 𝐏𝐚𝐭𝐭𝐞𝐫𝐧 https://lnkd.in/gzi447Pz Each article focuses on: When to use the pattern Clean implementation Real-world scenarios If you’re learning LLD or brushing up design patterns, this series should give you a solid foundation. #LLD #Java #DesignPatterns #Backend #SoftwareEngineering #SystemDesign

**Understanding the Singleton Design Pattern in C++** One instance. Controlled access. Global impact. The **Singleton Pattern** is one of the most widely used — and often misused — design patterns in software development. In this lesson from *The Ray Code*, I break it down in a practical, beginner-friendly way: • **What & Why** — when a single instance actually makes sense • **UML walkthrough** — visualize the structure clearly • **C++ code demo** — step-by-step implementation • **S.W.O.T. analysis** — strengths, weaknesses, opportunities, threats If you're learning **object-oriented design** or preparing for interviews, understanding Singleton is essential. 🎥 Watch here: [https://lnkd.in/g8x2qZxr) --- 💬 **Discussion:** Where have you used (or misused) Singleton in your projects?

I still remember the early days of my development career, spending hours debugging code that could have been simplified with the right design pattern. As I grew as a developer, I realized that understanding design patterns is crucial for writing efficient, scalable, and maintainable code. We've all been there - trying to fix a complex issue, only to realize that a simple creational pattern like Singleton or Factory could have prevented it. Having a solid grasp of design patterns can make a huge difference in the quality of our code. I've found that patterns like Observer, Strategy, and Template Method help me write more flexible and reusable code. They also make it easier for my team to collaborate and understand each other's work. By using the right design pattern, we can avoid common pitfalls and focus on delivering high-quality solutions. What are some design patterns that you think every developer should understand? Are there any specific patterns that have helped you simplify complex problems or improve your code quality? #DesignPatterns #SoftwareDevelopment #CodingBestPractices

🔄 Continuing my Design patterns learning journey… After understanding Creational Design Patterns, today I explored Structural Design Patterns — which focus on how different components of a system are structured and connected. 💡 Why Structural Patterns? They simplify complex systems by organizing relationships between classes and objects, making them easier to scale, extend, and maintain. 📌 Key Structural Design Patterns: 1️⃣ Adapter – Helps incompatible interfaces work together 2️⃣ Bridge – Separates abstraction from implementation for flexibility 3️⃣ Composite – Treats individual objects and groups uniformly 4️⃣ Decorator – Adds new behavior dynamically without changing existing code 5️⃣ Facade – Provides a simple interface to a complex system 6️⃣ Flyweight – Optimizes memory usage by sharing common data 7️⃣ Proxy – Controls access to an object (e.g., security, caching, lazy loading) 🧠 These patterns are especially useful when building scalable systems where components need to interact efficiently without tight coupling. 🚀 Tomorrow, I’ll dive into code implementations. #DesignPatterns #Java #BackendDevelopment

I still remember the early days of my development career, spending hours debugging code that could have been simplified with the right design pattern. As I grew as a developer, I realized that understanding design patterns is crucial for writing efficient, scalable, and maintainable code. We've all been there - stuck with a complex problem, wishing we had a blueprint to follow. Design patterns provide just that - a set of tried and tested solutions to common problems. They help us write code that is easy to understand, modify, and extend. I've found that having a solid grasp of patterns like Singleton, Factory, and Observer has saved me from a lot of headaches. It's not about memorizing a list of patterns, but about understanding the principles behind them and knowing when to apply them. So, what are some design patterns that you think every developer should understand? Are there any specific patterns that have helped you simplify your code or tackle a particularly tough problem? #designpatterns #softwaredevelopment #codingbestpractices

🚦 Designing a Traffic Light System — Using State Design Pattern Ever noticed how a traffic light smoothly changes from Red → Green → Yellow without confusion............... It looks simple, but behind the scenes, each color represents a different behavior. I recently built a mini version of this system in Java, and it turned into a great example of using the State Design Pattern effectively. 🧩 The Problem We have a traffic light with multiple states: 🔴 Red → Stop 🟢 Green → Go 🟡 Yellow → Slow down Now the challenge: 👉 The system should behave differently based on its current state 👉 And it should be easy to add new states like: Blinking (night mode) Maintenance mode ❌ The Naive Approach Most people start with: if (color.equals("RED")) { ... } else if (color.equals("GREEN")) { ... } else if (color.equals("YELLOW")) { ... } 🚫 Problems: Not scalable Becomes messy with more states Violates Open/Closed Principle Hard to maintain ✅ The Better Approach: State Design Pattern We shift from conditions → objects Instead of one class handling everything: 👉 Each state becomes its own class ⚙️ How It Works Step 1: Define a State Interface Each state defines what happens next Step 2: Create Separate State Classes RedState → decides next = Green GreenState → decides next = Yellow YellowState → decides next = Red Each state controls its own behavior 🔥 Step 3: Context Class (TrafficLight) 👉 Holds the current state 👉 Delegates behavior to that state 👉 The context doesn’t care how things work internally 🔥 Why This Design Wins ✅ Open/Closed Principle Add new modes without modifying old code ✅ High Cohesion Each class = one responsibility ✅ Low Coupling States don’t interfere with each other ✅ Cleaner Thinking You model real-world behavior naturally 🌍 Real-World Use Cases 🎬 Media players (Play, Pause, Stop) 🥤 Vending machines (NoCoin, HasCoin) 📄 Document workflows (Draft, Review, Published) 🎮 Game characters (Idle, Running, Attacking) 🚀 Interview Insight If you explain this well, you show: 1. Real understanding of design patterns 2. Ability to write scalable code 3. Strong problem-solving mindset #SystemDesign #Java #DesignPatterns #StatePattern #CleanCode #SoftwareEngineering #InterviewPrep

𝐃𝐞𝐬𝐢𝐠𝐧 𝐏𝐚𝐭𝐭𝐞𝐫𝐧𝐬 𝐟𝐨𝐫 𝐄𝐯𝐞𝐫𝐲 𝐃𝐞𝐯𝐞𝐥𝐨𝐩𝐞𝐫 𝐋𝐞𝐯𝐞𝐥 𝐉𝐮𝐧𝐢𝐨𝐫 → Write clean, flexible code (Builder, Factory, Singleton, Decorator) 𝐌𝐢𝐝→ Build scalable & modular systems (Strategy, Adapter, Facade, Command) 𝐒𝐞𝐧𝐢𝐨𝐫→ Handle complexity like a pro (Prototype, State, Proxy, Interpreter) Patterns aren’t just concepts — they’re your shortcut to writing better code faster. Follow Madhu K. for more coding & system design content #DesignPatterns #SoftwareEngineering #Java #SystemDesign #Coding