Java's Subtle Behaviors: 3 Surprising Edge Cases

🚀 Hey folks! I’m back with a Java concept — let’s decode Singleton in the simplest way possible 😄 🤔 What is Bill Pugh Singleton? (pronounced like “Bill Pew” 😄) Many of you know the Singleton pattern, but did you know there are multiple ways to implement it? 👉 Let’s quickly list them: 1️⃣ Eager Initialization 2️⃣ Lazy Initialization 3️⃣ Synchronized Singleton 4️⃣ Double-Checked Locking 5️⃣ Bill Pugh Singleton (Best Practice ⭐) 6️⃣ Enum Singleton (Most Secure) 🧠 Why Bill Pugh Singleton? It was popularized by Java expert Bill Pugh as a clean + efficient solution. 👉 It uses: Static inner class JVM class loading No locks, no volatile 🔥 Key Benefits ✔ Lazy loading (created only when needed) ✔ Thread-safe ✔ No synchronized overhead ✔ High performance ✔ Clean & simple ⚙️ How It Works (Internally) Step 1: Class Load Singleton s = Singleton.getInstance(); 👉 Only outer class loads ❗ Inner class NOT loaded yet Step 2: Method Call return Holder.INSTANCE; 👉 Now JVM triggers inner class loading Step 3: Inner Class Loads private static class Holder 👉 Loaded ONLY when accessed (Lazy 🔥) Step 4: Object Creation private static final Singleton INSTANCE = new Singleton(); 👉 Created once, safely 🔒 Why It’s Thread-Safe? JVM guarantees during class loading: ✔ Only ONE thread initializes ✔ Other threads WAIT ✔ Fully initialized object is shared 👉 Comes from Java Memory Model (JMM) ⚠️ Important Concept: Partial Construction What you THINK happens: Allocate memory Initialize object Assign reference What CAN happen (Reordering ❌): Allocate memory Assign reference ⚠️ Initialize object 💥 Real Problem Thread-1: instance = new Singleton(); Thread-2: System.out.println(instance.value); 👉 Output: Expected: 42   Actual:  0 ❌ 🚨 Object is visible BEFORE full initialization 👉 This is Partial Construction 🛠️ How volatile Fixes It (in DCL) private static volatile Singleton instance; ✔ Prevents reordering ✔ Ensures visibility ✔ Guarantees fully initialized object 🔥 Why Bill Pugh Avoids This? private static class Holder {   private static final Singleton INSTANCE = new Singleton(); } 👉 JVM ensures: No reordering No partial construction Happens-before guarantee 🧵 Internal Flow Thread-1 → creates instance Thread-2 → waits Thread-3 → waits 👉 All get SAME object 🏢 Simple Analogy Main Office = Singleton Storage Room = Holder 🚪 Room stays locked 👉 Opens only when needed 👉 Item created once 👉 Everyone uses same item ⚠️ Limitations ❌ Reflection can break it ❌ Serialization can break it 👉 Use Enum Singleton to fix these 🏁 Final Takeaway 👉 Bill Pugh = Lazy + Thread Safe + No Locks 🚀 💬 If this helped you understand Singleton better, drop a 👍 #Java #Multithreading #DesignPatterns #InterviewPrep #BackendDevelopment

🚀 Top 5 Tough Java Questions Asked in GCC Interviews (2026) — With Answers Cracking GCC companies today is not about syntax… it’s about how you think, design, and scale systems. Here are 5 real tough Java questions trending in interviews 👇 --- 1️⃣ Explain Java Memory Model (JMM) & Happens-Before Relationship 💡 Why they ask: Tests deep concurrency understanding ✅ Answer: - JMM defines how threads interact through memory (heap, stack) - Happens-before ensures visibility + ordering guarantees - Example: - Write to variable → happens-before → another thread reads it - Without it → race conditions / stale data 👉 Key point: "volatile", "synchronized", locks enforce happens-before --- 2️⃣ How would you design a thread-safe Singleton in Java? 💡 Why they ask: Tests design + concurrency ✅ Answer (Best approach): public class Singleton { private Singleton() {} private static class Holder { private static final Singleton INSTANCE = new Singleton(); } public static Singleton getInstance() { return Holder.INSTANCE; } } ✔ Lazy loaded ✔ Thread-safe ✔ No synchronization overhead --- 3️⃣ HashMap Internals – What happens during collision? 💡 Why they ask: Tests core + performance thinking ✅ Answer: - Uses array + linked list / tree (Java 8+) - Collision → same bucket index - Java 8: - LinkedList → converts to Red-Black Tree after threshold - Improves from O(n) → O(log n) 👉 Key: Good "hashCode()" + "equals()" matters --- 4️⃣ Difference between "synchronized", "ReentrantLock", and "volatile" 💡 Why they ask: Real-world concurrency decisions ✅ Answer: Feature| synchronized| ReentrantLock| volatile Locking| Yes| Yes (flexible)| No Fairness| No| Yes (optional)| No Interruptible| No| Yes| No Visibility| Yes| Yes| Yes 👉 Use: - "volatile" → visibility only - "synchronized" → simple locking - "ReentrantLock" → advanced control --- 5️⃣ How would you design a scalable REST API using Spring Boot? 💡 Why they ask: System design + real work ✅ Answer: - Use layered architecture (Controller → Service → Repository) - Apply: - Caching (Redis) - Async processing ("CompletableFuture") - Circuit breaker (Resilience4j) - Ensure: - Idempotency - Rate limiting - Proper exception handling 👉 Bonus: Use microservices + event-driven design --- 🔥 Pro Tip: In 2026, interviews focus on: - JVM internals - Concurrency - System design - Real production scenarios --- 💬 Which question surprised you the most? ♻️ Save this for your next interview prep! Do comment and like for more reach!!! #Java #GCC #InterviewPrep #Backend #SpringBoot #SoftwareEngineering

What Does a Java Full Stack Developer Interview Typically Cover? What a Java Full Stack Developer is expected to do:  Back-End: Java, Spring Boot, REST APIs, databases (SQL/NoSQL) Front-End: HTML, CSS, JavaScript, and frameworks like React, Angular, or Vue Tools & DevOps: Git, Docker, Jenkins, Maven/Gradle, CI/CD Soft Skills: Problem-solving, communication, teamwork Key Tips to Crack the Interview 1. Master the Basic Concepts of Java Concentrates on: OOP principles- Inheritance, Encapsulation, Polymorphism, and Abstraction Collections Framework Multithreading and Concurrency Exceptions Handling  Java 8+ features- Streams, Lambdas, Optional, Functional Interfaces. 2. Understand With Backend Frameworks (Spring, Spring Boot) Build REST APIs Using Annotation like @RestController, @Service, @Autowired Connect to databases using JPA/Hibernate Handle Exception globally Secure the API with Spring Security. 3. Be Good at Front End Development Key skills: HTML, CSS, and JavaScript(ES6+) Basics of React.js or Angular State Management, (Redux, useState, useEffect) Consume REST APIs  Responsive design using Bootstrap or Material UI 4. Refresh Your Knowledge of Databases Be prepared to: Write optimized SQL queries. Normalize database schemas. Work with PostgreSQL/MySQL/MongoDB. Use JPA/Hibernate to perform CRUD operations. 5. Refresh Basic System Design REST vs. SOAP Microservices vs. Monolithic Scalability, Load Balancing, and Caching API Gateway and Service Registry Database Partitioning and Replication Top Interview Questions by Category Core Java What are List, Set, and Map in Java? How does garbage collection work in Java? Explain synchronized versus volatile versus thread-safe collections. What are the differences between HashMap and ConcurrentHashMap?  What are the benefits of using Streams and Lambdas for a cleaner, more beautiful way of Java programming? Spring Boot What are the differences between Spring and Spring Boots How does Spring handle Dependency Injection? What is the use of @RestController, @RequestMapping, @PathVariable, and @RequestParam? How do you globally handle exceptions in Spring Boot? How to perform JWT-based authentication in Spring Boot? Frontend(React/Angular) What is the props and state difference in React? How do React Hooks such as useEffect and useState work? What are React lifecycle methods? Database Write a SQL query to find the second-highest salary in a table. What is implemented by Join and the reason for using it? What do you mean by ACID properties in transactions? How does JPA manage relationships such as OneToMany, ManyToMany? How to avoid a Hibernate N+1 problem? DevOps & Tools How do you deploy a Spring Boot app using Docker? What is the role of CI/CD in the full-stack development life cycle? How are you using Git for version control in a team setting? What's the difference between Maven and Gradle? How do you keep track of logs in production? Learn More at Softronix!

⏳Day 28 – 1 Minute Java Clarity – ArrayList vs LinkedList Both are Lists… but they work very differently! ⚡ 📌 ArrayList: Backed by a dynamic array internally. 👉 Best for frequent read/search operations. 📌 LinkedList: Backed by a doubly linked list internally. 👉 Best for frequent insert/delete operations. 📌 Example: import java.util.*; public class ListComparison {   public static void main(String[] args) {     // ArrayList     List<String> arrayList = new ArrayList<>();     arrayList.add("Alice");     arrayList.add("Bob");     arrayList.add(1, "Charlie"); // insert at index 1 – slow!     System.out.println(arrayList); // [Alice, Charlie, Bob]     // LinkedList     LinkedList<String> linkedList = new LinkedList<>();     linkedList.add("Alice");     linkedList.add("Bob");     linkedList.addFirst("Charlie"); // insert at start – fast! ✅     System.out.println(linkedList); // [Charlie, Alice, Bob]   } } 📌 Head-to-Head Comparison: | Feature | ArrayList | LinkedList | |---|---|---| | Internal Structure | Dynamic Array | Doubly Linked List | | Search (get) | O(1) ⚡ Fast | O(n) 🐢 Slow | | Insert/Delete (middle) | O(n) 🐢 Slow | O(1) ⚡ Fast | | Memory | Less (stores data) | More (stores data + pointers) | | Best for | Read-heavy apps | Write-heavy apps | 💡 Real-time Example: 📚 Library System: ArrayList → Finding a book by shelf number (direct index access) ⚡ LinkedList → Adding/removing books frequently from shelves (no shifting needed) ✅ ⚠️ Interview Trap: Which is faster for iteration? 👉 ArrayList is faster for iteration due to memory locality (cache friendly). 👉 LinkedList nodes are scattered in memory → more cache misses. 📌 Pro Tip: // Use ArrayList by default List<String> list = new ArrayList<>(); // Switch to LinkedList only when insert/delete at ends is the main operation Deque<String> deque = new LinkedList<>(); // used as a Queue/Stack 💡 Quick Summary: ✔ ArrayList → fast read, slow insert/delete (middle) ✔ LinkedList → slow read, fast insert/delete ✔ ArrayList uses less memory ✔ LinkedList doubles as a Queue and Stack ✔ Default choice → ArrayList ✅ 🔹 Next Topic → HashMap Deep Dive in Java Did you know ArrayList grows by 50% of its size when full? Drop 🔥 if this was new to you! #Java #ArrayList #LinkedList #JavaCollections #CoreJava #JavaProgramming #JavaDeveloper #BackendDeveloper #1MinuteJavaClarity #100DaysOfCode #DataStructures

*⚡ Control Flow in Java (if-else & switch)* *✅ 1️⃣ What is Control Flow?* 👉 Control Flow determines which code runs and when. Example: If condition is true → do this Else → do something else *✅ 2️⃣ if Statement* Used when you want to execute code only if a condition is true. if (condition) { // code } Example: int age = 20; if (age >= 18) { System.out.println("You can vote"); } *✅ 3️⃣ if-else Statement* Used when you want two outcomes. if (condition) { // true block } else { // false block } Example: int age = 16; if (age >= 18) { System.out.println("Adult"); } else { System.out.println("Minor"); } *✅ 4️⃣ if-else if Ladder* Used when you have multiple conditions. int marks = 85; if (marks >= 90) { System.out.println("A Grade"); } else if (marks >= 75) { System.out.println("B Grade"); } else if (marks >= 50) { System.out.println("C Grade"); } else { System.out.println("Fail"); } *🔥 Important Rule ⭐* 👉 Conditions are checked top to bottom 👉 First true condition executes → rest are skipped *✅ 5️⃣ Nested if* 👉 if inside another if int age = 20; boolean hasID = true; if (age >= 18) { if (hasID) { System.out.println("Allowed"); } } *✅ 6️⃣ switch Statement* Used when you have multiple fixed values. 👉 Cleaner than multiple if-else switch (variable) { case value1: // code break; case value2: // code break; default: // code } Example: int day = 2; switch (day) { case 1: System.out.println("Monday"); break; case 2: System.out.println("Tuesday"); break; default: System.out.println("Invalid"); } *🔥 Important Concepts (switch ⭐)* 1️⃣ break keyword 👉 Stops execution after a case Without break: case 1: System.out.println("Monday"); case 2: System.out.println("Tuesday"); 👉 Output: Monday Tuesday 2️⃣ default case 👉 Runs when no case matches *✅ 7️⃣ When to Use What?* - Simple condition: Use if - Two outcomes: Use if-else - Multiple conditions: Use if-else if - Fixed values: Use switch *🔥 Example Program* 👉 This program performs two tasks: 1️⃣ Checks whether a number is positive or negative 2️⃣ Prints the day based on a number using switch class ControlFlowDemo { public static void main(String[] args) { int number = 10; if (number > 0) { System.out.println("Positive"); } else { System.out.println("Negative"); } int day = 1; switch (day) { case 1: System.out.println("Monday"); break; default: System.out.println("Other day"); } } } ✔ Checks number → Positive/Negative ✔ Uses switch → prints day ✔ Uses break → stops execution ✔ Uses default → fallback *⭐ Common Interview Questions* - Difference between if-else and switch - When to use switch over if - What happens if break is missing? - Can we use String in switch? (👉 Yes, Java 7+) *🔥 Quick Revision* if → single condition if-else → two outcomes if-else if → multiple conditions

*⚡ Control Flow in Java (if-else & switch)* *✅ 1️⃣ What is Control Flow?* 👉 Control Flow determines which code runs and when. Example: If condition is true → do this Else → do something else *✅ 2️⃣ if Statement* Used when you want to execute code only if a condition is true. if (condition) { // code } Example: int age = 20; if (age >= 18) { System.out.println("You can vote"); } *✅ 3️⃣ if-else Statement* Used when you want two outcomes. if (condition) { // true block } else { // false block } Example: int age = 16; if (age >= 18) { System.out.println("Adult"); } else { System.out.println("Minor"); } *✅ 4️⃣ if-else if Ladder* Used when you have multiple conditions. int marks = 85; if (marks >= 90) { System.out.println("A Grade"); } else if (marks >= 75) { System.out.println("B Grade"); } else if (marks >= 50) { System.out.println("C Grade"); } else { System.out.println("Fail"); } *🔥 Important Rule ⭐* 👉 Conditions are checked top to bottom 👉 First true condition executes → rest are skipped *✅ 5️⃣ Nested if* 👉 if inside another if int age = 20; boolean hasID = true; if (age >= 18) { if (hasID) { System.out.println("Allowed"); } } *✅ 6️⃣ switch Statement* Used when you have multiple fixed values. 👉 Cleaner than multiple if-else switch (variable) { case value1: // code break; case value2: // code break; default: // code } Example: int day = 2; switch (day) { case 1: System.out.println("Monday"); break; case 2: System.out.println("Tuesday"); break; default: System.out.println("Invalid"); } *🔥 Important Concepts (switch ⭐)* 1️⃣ break keyword 👉 Stops execution after a case Without break: case 1: System.out.println("Monday"); case 2: System.out.println("Tuesday"); 👉 Output: Monday Tuesday 2️⃣ default case 👉 Runs when no case matches *✅ 7️⃣ When to Use What?* - Simple condition: Use if - Two outcomes: Use if-else - Multiple conditions: Use if-else if - Fixed values: Use switch *🔥 Example Program* 👉 This program performs two tasks: 1️⃣ Checks whether a number is positive or negative 2️⃣ Prints the day based on a number using switch class ControlFlowDemo { public static void main(String[] args) { int number = 10; if (number > 0) { System.out.println("Positive"); } else { System.out.println("Negative"); } int day = 1; switch (day) { case 1: System.out.println("Monday"); break; default: System.out.println("Other day"); } } } ✔ Checks number → Positive/Negative ✔ Uses switch → prints day ✔ Uses break → stops execution ✔ Uses default → fallback *⭐ Common Interview Questions* - Difference between if-else and switch - When to use switch over if - What happens if break is missing? - Can we use String in switch? (👉 Yes, Java 7+) *🔥 Quick Revision* if → single condition if-else → two outcomes if-else if → multiple conditions

⏳Day 25 – 1 Minute Java Clarity – throw vs throws Two words, one letter difference… huge impact! ⚡ 📌 What is throw? Used to manually throw an exception inside a method. 👉 Followed by an exception object. 📌 What is throws? Used to declare that a method might throw an exception. 👉 Written in the method signature. 📌 Example: class AgeValidator {   // throws declares the exception   void validateAge(int age) throws IllegalArgumentException {     if (age < 18) {       throw new IllegalArgumentException("Age must be 18+"); // throw triggers it     }     System.out.println("Access granted ✅");   }   public static void main(String[] args) {     AgeValidator av = new AgeValidator();     try {       av.validateAge(15);     } catch (IllegalArgumentException e) {       System.out.println(e.getMessage());     }   } } 📌 Key Differences at a Glance: | Feature | throw | throws | | Purpose | Trigger an exception | Declare an exception | | Location | Inside method body | Method signature | | Followed by | Exception object | Exception class name | | Count | One exception at a time | Multiple allowed | 💡 Real-time Example: Think of a security guard 🏢 throw → Guard physically stops you ("You can't enter!") throws → Sign on the door ("ID required to enter") ⚠️ Interview Trap: Can throw handle checked exceptions without try-catch? 👉 NO! Checked exceptions thrown via `throw` must be caught or declared with `throws`! 📌 Quick Tip: java // Multiple exceptions with throws void readFile() throws IOException, FileNotFoundException {   // code } 💡 Quick Summary: ✔ throw → manually raises an exception (action) ✔ throws → warns callers about possible exceptions (declaration) ✔ throw is inside the method, throws is on the method ✔ throw handles one; throws can declare many 🔹 Next Topic → Custom Exceptions in Java Did you know you can throw any object that extends Throwable? Drop 🔥 if this was clear! #Java #ThrowVsThrows #ExceptionHandling #CoreJava #JavaProgramming #JavaDeveloper #BackendDeveloper #1MinuteJavaClarity #100DaysOfCode #Coding

Stop writing Java Switch statements like it’s 2004!   If you are still writing switch statements with break; at the end of every line, you are living in the past! Java has transformed the humble switch from a clunky branching tool into a powerful, functional expression.   Here is the evolution of how we control logic in Java:   1️⃣ The "Classic" Era (Java 1.0 - 6) * Syntax: case X: ... break; * Limitation: Only primitives (int, char) and Enums. * The Risk: "Fall-through" bugs. Forget one break and your logic cascades into chaos. 2️⃣ The "Modern Expression" (Java 14) Java 14 turned the Switch into an Expression. It can now return a value! * Arrow Syntax (->): No more break. It’s cleaner and safer. * Assignment: var result = switch(val) { ... }; * Yield: Use yield to return values from complex multi-line blocks.   3️⃣ The "Pattern Matching" Powerhouse (Java 21) This is the game changer. Switch is no longer just for values; it’s for Types.   * Case Patterns: Switch directly on an Object. * Automatic Casting: No more instanceof followed by manual casting. * Guarded Patterns: Use the when keyword to add logic filters directly into the case.  * Null Safety: Explicitly handle case null without crashing. Sample : /** * SCENARIO: Processing a result object that could be  * a String, an Integer, or a custom Status record.  */ // 🛑 THE OLD WAY (Java 8) - Verbose and manual public String handleResultOld(Object result) {    if (result == null) {    return "Unknown";  }  if (result instanceof String) {    String s = (String) result; // Manual casting    return "Message: " + s;  } else if (result instanceof Integer) {    Integer i = (Integer) result;    return "Code: " + i;  }  return "Unsupported"; } // ✅ THE MODERN WAY (Java 21) - Concise and Type-Safe   public String handleResultModern(Object result) {  return switch (result) {    case null -> "Unknown";    case String s when s.isBlank() -> "Empty Message";    case String s -> "Message: " + s; // Automatic casting    case Integer i -> "Code: " + i;    default -> "Unsupported";  };  }   #Java21 #ModernJava #BackendDevelopment #Coding #TechCommunity #Developers #LearningToCode

💡 Functional Interfaces in Java — Beyond the Basics If you think Functional Interfaces are just about Lambda expressions, you're only scratching the surface. Let’s go deeper 👇 🔹 Recap: What is a Functional Interface? An interface with exactly one abstract method, annotated optionally with "@FunctionalInterface" for clarity and compile-time safety. --- 🔹 Key Characteristics ✔ Can have multiple default and static methods ✔ Enables functional programming style in Java ✔ Works seamlessly with lambda expressions and method references --- 🔹 Custom Functional Interface Example @FunctionalInterface interface Calculator { int operate(int a, int b); } Usage: Calculator add = (a, b) -> a + b; System.out.println(add.operate(5, 3)); // 8 --- 🔹 Lambda vs Method Reference Lambda: (a, b) -> a + b Method Reference: Integer::sum 👉 Cleaner and more reusable when method already exists. --- 🔹 Where are Functional Interfaces Used? 🔥 1. Streams API list.stream() .filter(x -> x > 10) // Predicate .map(x -> x * 2) // Function .forEach(System.out::println); // Consumer 🔥 2. Multithreading new Thread(() -> System.out.println("Running thread")).start(); 🔥 3. Event Handling & Callbacks Used heavily in asynchronous and reactive programming. --- 🔹 Types of Functional Interfaces (Deep View) ✨ Predicate<T> → Boolean conditions Used for filtering data ✨ Function<T, R> → Transformation Convert one form of data to another ✨ Consumer<T> → Performs action Logging, printing, updating ✨ Supplier<T> → Generates data Lazy loading, object creation ✨ BiFunction / BiPredicate → Work with 2 inputs --- 🔹 Why Companies Care? (Interview Insight) ✔ Reduces boilerplate code ✔ Encourages clean architecture ✔ Essential for Spring Boot & Microservices ✔ Frequently used in real-world production code --- 🔹 Common Mistakes to Avoid ❌ Adding more than one abstract method ❌ Ignoring built-in functional interfaces ❌ Overusing lambdas (readability matters!) --- 🔹 Pro Tip for Freshers 🚀 When solving DSA or backend problems, try rewriting logic using: 👉 Lambda expressions 👉 Streams 👉 Built-in functional interfaces This shows modern Java proficiency in interviews. --- 💬 Final Thought: Functional Interfaces are not just a feature—they represent a shift in how Java developers think and write code. Master them, and your code becomes shorter, smarter, and more powerful ⚡ #Java #FunctionalProgramming #Java8 #BackendDeveloper #CodingJourney #SoftwareEngineering #InterviewPrep

🚀 One of the Most Complex Java Problems Asked in Top Tech Interviews 💡 Design a Thread-Safe LRU Cache with O(1) Operations --- 🧠 Problem Statement: Design and implement an LRU (Least Recently Used) Cache with the following operations: - "get(key)" → Returns value if present, else -1 - "put(key, value)" → Insert/update the value ⚡ Constraints: - Both operations must run in O(1) time - Must be thread-safe (handle concurrent access properly) --- 🔥 Why this is challenging? This problem tests: - Data Structures (HashMap + Doubly Linked List) - Concurrency (Locks, synchronization) - Real-world system design (cache eviction strategy) --- 🛠️ Approach: To achieve O(1): - Use a HashMap → Fast lookup - Use a Doubly Linked List → Maintain LRU order For Thread Safety: - Use ReentrantLock (better than synchronized for flexibility) --- 💻 Java Implementation: import java.util.*; import java.util.concurrent.locks.ReentrantLock; class LRUCache { class Node { int key, value; Node prev, next; Node(int k, int v) { key = k; value = v; } } private final int capacity; private Map<Integer, Node> map; private Node head, tail; private ReentrantLock lock = new ReentrantLock(); public LRUCache(int capacity) { this.capacity = capacity; this.map = new HashMap<>(); head = new Node(0, 0); tail = new Node(0, 0); head.next = tail; tail.prev = head; } public int get(int key) { lock.lock(); try { if (!map.containsKey(key)) return -1; Node node = map.get(key); remove(node); insert(node); return node.value; } finally { lock.unlock(); } } public void put(int key, int value) { lock.lock(); try { if (map.containsKey(key)) { remove(map.get(key)); } if (map.size() == capacity) { Node lru = tail.prev; remove(lru); map.remove(lru.key); } Node newNode = new Node(key, value); insert(newNode); map.put(key, newNode); } finally { lock.unlock(); } } private void remove(Node node) { node.prev.next = node.next; node.next.prev = node.prev; } private void insert(Node node) { node.next = head.next; node.prev = head; head.next.prev = node; head.next = node; } } --- ⚠️ Common Mistakes: - Forgetting to update order after "get()" - Not handling concurrency → leads to race conditions - Using only HashMap (misses LRU behavior) --- 📈 Follow-up Questions Asked in Interviews: - Can you make it lock-free? - How would you scale this in distributed systems? - What if capacity is millions? #Java #SystemDesign #CodingInterview #Concurrency #TechCareers