Mohamed Aymen Elarbi’s Post

💡 Today I Learned: What Happens If Two Keys Have the Same hashCode in HashMap? While preparing for Java interviews, I explored an interesting scenario: 👉 What if two different keys have the same hashCode() but are NOT equal? Here’s what actually happens inside HashMap: 1️⃣ HashMap uses the hashCode to find the bucket index. 2️⃣ If two keys land in the same bucket, a collision occurs. 3️⃣ Then HashMap uses equals() to compare keys. 4️⃣ If keys are not equal, both entries are stored in the same bucket. 🔎 Before Java 8 → collisions were stored using LinkedList. 🔎 From Java 8 → if bucket size exceeds threshold (default 8), it converts into a Balanced Tree (Red-Black Tree) for better performance. 📌 Key Insight: HashMap does NOT rely only on hashCode — it always checks equals() before deciding uniqueness. Understanding this helped me realize why properly overriding both hashCode() and equals() is critical. Still learning and improving every day 🚀 #Java #DataStructures #InterviewPreparation #BackendDeveloper #LearningInPublic

💡 One Java Question That Almost Every Interview Includes: HashMap While revisiting core Java concepts today, I went deep into how HashMap actually works internally — something many developers use daily but don’t always fully understand. Here are a few powerful takeaways: 🔹 How "HashMap.put()" stores data internally 🔹 How "HashMap.get()" retrieves values efficiently 🔹 What Hash Collisions are and how Java handles them 🔹 Why "equals()" and "hashCode()" are critical in HashMap 🔹 The Java 8 optimization where buckets convert from LinkedList ➝ Red-Black Tree 🔹 How this improves search complexity from O(n) ➝ O(log n) when collisions increase Understanding these internals is not just useful for interviews — it actually helps write better and more efficient Java code. If you're preparing for Java developer interviews or strengthening core. concepts, this explanation is worth watching. 🎥 https://lnkd.in/dcNyYqVG #Java #JavaDeveloper #HashMap #JavaInterviewQuestions #BackendDevelopment #SoftwareEngineering #LearningInPublic

Java Collections Framework Explained in Simple Terms. The Java Collections Framework provides powerful data structures and algorithms to manage data effectively. Commonly used classes: ✔ ArrayList ✔ LinkedList ✔ HashSet ✔ TreeSet ✔ HashMap ✔ PriorityQueue Each has different performance characteristics (Time Complexity matters!) 👉 Choosing the right collection improves performance and scalability of applications. Are you confident in explaining internal working of HashMap in interviews? 🤔 #JavaDeveloper #CollectionsFramework #CodingInterview #TechLearning

🚀 Java Interview Question Series What is the difference between HashMap and ConcurrentHashMap? HashMap: ❌ Not thread safe ❌ Multiple threads can modify data simultaneously ConcurrentHashMap: ✅ Thread safe ✅ Allows concurrent read/write operations Used in multithreaded environments. Many developers fail this simple interview question. Follow me for more Java interview questions and coding tips. 💻 #Java #Programming #CodingInterview #SoftwareDevelopment

Overriding equals() vs hashCode() in Java This is a VERY important interview question for Java placements and LinkedIn interviews. It is mainly asked in Collections topic (especially with HashMap, HashSet). 🔹 1️⃣ equals() Method Defined in java.lang.Object Used to compare content equality Default implementation compares memory address 🔹 2️⃣ hashCode() Method Also defined in java.lang.Object Returns integer hash value Used internally by hashing collections like: HashMap HashSet Hashtable So: 👉 equals() checks equality 👉 hashCode() decides bucket location Thankful to my mentor, Anand Kumar Buddarapu, and the practice sessions that continue to strengthen my core Java knowledge. Continuous learning is the key to growth!  #Java #Collections  #BackendDevelopment  #Coding

Do You Know How HashMap Works Internally in Java? As a Java Backend Developer, understanding fundamentals is very important for cracking interviews and writing efficient code. Here’s a quick breakdown of how HashMap works internally: ✅ HashMap stores data in key-value pairs ✅ It uses an array of buckets internally ✅ When we insert a key: HashMap calculates the hashcode() It converts it into a bucket index If collision happens → it uses LinkedList (Java 7) or Tree (Red-Black Tree in Java 8) 💡 Important Points: Default initial capacity = 16 Load factor = 0.75 Not synchronized (not thread-safe) Allows one null key and multiple null values Why is this important? Because interviewers don’t just ask “What is HashMap?” They ask: What happens during collision? How resizing works? Difference between HashMap and ConcurrentHashMap? Why is HashMap not thread-safe? Understanding internals makes you a better backend developer. I’m currently strengthening my Java fundamentals and diving deeper into Spring Boot and backend architecture. #Java #SpringBoot #BackendDevelopment #JavaDeveloper #InterviewPreparation #Programming Durgesh Tiwari Harsh Mishra

🚨 One Java Interview Question Many Developers Still Get Wrong equals() vs hashCode() Most developers know these methods exist in Java, but many don’t fully understand why they must work together. Let’s break it down 👇 🔹 equals() • Used to compare the logical equality of two objects • By default, it compares memory references, not values • We override it when we want to compare object content 🔹 hashCode() • Returns an integer hash value for the object • Used internally by HashMap, HashSet, and HashTable • Helps Java quickly locate objects in hash buckets ⚠️ Important Rule If two objects are equal using equals(), they must return the same hashCode(). Otherwise, collections like HashSet or HashMap may behave incorrectly. 💡 Example Issue You add two logically equal objects into a HashSet, but because their hashCode values are different, both get stored. Result? Duplicate objects inside a Set. ✅ Takeaway Whenever you override equals(), always override hashCode() as well. This small rule can prevent subtle and hard-to-debug issues in real applications. 💬 Have you ever faced a bug related to equals() and hashCode()? #Java #SoftwareDevelopment #Programming #JavaDeveloper #CodingInterview #BackendDevelopment

🚀 Learning Java the Right Way Today, I practiced one of the most popular interview questions — 👉 Two Sum Problem. 📌 Problem: Given an array of integers and a target value, find two numbers that add up to the target. Example: Array = {2, 7, 11, 15} Target = 9 Output → 2 + 7 = 9 ✅ 🔹 What I learned: Instead of using nested loops (O(n²)), I solved it using a HashMap for an optimized O(n) solution. ✔ Used complement logic → target - currentElement ✔ Stored visited elements in HashMap ✔ Checked pair existence in a single pass This problem strengthens: • Logical thinking • Optimization mindset • HashMap concepts • Real interview preparation Understanding when to optimize from brute-force to efficient solutions is what makes a developer grow 🚀 📌 Think smart • Code clean • Optimize always 💡 #java #javafullstack #javadeveloper #corejava #codingjourney #coding

This was a question I was recently asked in an interview: 👉 Is Java a purely object-oriented language? At first glance, many people say “Yes” because Java strongly follows core OOPS principles: • Encapsulation • Inheritance • Polymorphism • Abstraction However, the correct answer is: Java is not a purely object-oriented language. Here’s why: • Java supports primitive data types like int, double, char, and boolean, which are not objects. • We can define and use static methods and variables without creating objects. In a purely object-oriented language, everything must be treated as an object. Java is strongly object-oriented, but not purely object-oriented. Conceptual questions like this often test clarity of fundamentals more than coding ability. #Java #OOPS #InterviewPreparation #SoftwareEngineering #BackendDevelopment

🚀 A Java Interview Experience Recently had an interesting technical discussion for a Java-based role. The conversation was not limited to basic theory it focused more on understanding how things work internally and how concepts are applied in real applications. The discussion started around my projects and gradually moved into deeper Java and backend concepts. Some of the topics and questions that came up: • How HashMap works internally and how collisions are handled • Difference between fail-fast and fail-safe iterators in Java Collections • What happens inside the JVM when a Java program runs • Explain Garbage Collection mechanisms and different GC types • Difference between Comparable and Comparator with use cases • How multithreading works in Java and difference between Runnable and Thread • What are synchronization issues and race conditions • How REST APIs are designed in backend applications • Writing optimized SQL queries with JOINs and indexing concepts • Discussion around project architecture and design decisions What stood out was that the focus was not just on answers, but on how well concepts are understood and explained with practical scenarios. Experiences like this always help in identifying areas to improve and strengthening the overall understanding of backend development. Looking forward to more such technical discussions and continuous learning. #Java #BackendDevelopment #InterviewExperience #SoftwareEngineering #JavaDeveloper #TechLearning