Java HashMap Internals: Key-Value Pairs, Hashing, and Resizing

📌 HashSet vs HashMap in Java — Understanding the Core Difference In the Java Collections Framework, both HashSet and HashMap are widely used — but they serve different purposes. 🔹 HashSet Implements the Set interface Stores unique elements only Does not maintain insertion order Internally backed by a HashMap Does not allow duplicate values Used when you only care about storing unique data. 🔹 HashMap Implements the Map interface Stores key–value pairs Keys must be unique (values can be duplicated) Does not maintain insertion order Provides fast lookup using hashing Used when you need to associate a value with a unique key. 💡 Key Difference: HashSet stores only values (unique elements), while HashMap stores key–value pairs. Understanding this difference helps you choose the right data structure for performance, scalability, and clean design. #Java #CoreJava #CollectionsFramework #HashSet #HashMap #JavaDeveloper #BackendDevelopment #Programming #JavaProgramming #LearnJava #JavaCollections #DataStructures #SoftwareDeveloper #BackendEngineer #CodingLife #TechLearning #ProgrammingConcepts

Hello Java Developers, 🚀 Day 16 – Java Revision Series Today’s topic: Internal Working of LinkedHashMap — the perfect blend of HashMap performance and predictable iteration order. 💡 LinkedHashMap = Hash table + Doubly Linked List 🔹 Internals: Uses the same bucket array as HashMap for O(1) average access Each entry also participates in a doubly-linked list (before / after) This maintains insertion-order or access-order 🔹 How put() works: Compute hash → find bucket Handle collision like HashMap Insert node into bucket and append it to the linked list tail 🔹 How get() works: Compute hash → search bucket using equals() If access-order is enabled, the accessed node is moved to the tail 🎯 Why it matters: Predictable iteration order Great for LRU cache implementations Slightly more memory than HashMap, but same average O(1) performance 📄 I’ve shared a PDF with diagrams + step-by-step flow for quick revision. #Java #CoreJava #LinkedHashMap #JavaInternals #DataStructures #InterviewPreparation #LearningInPublic

Today I revised the differences between HashMap, LinkedHashMap, and TreeMap in Java. 🔹 HashMap – Stores data as key-value pairs, does not maintain order, allows one null key and multiple null values. 🔹 LinkedHashMap – Similar to HashMap but maintains insertion order. 🔹 TreeMap – Stores data in sorted order (ascending by keys) and does not allow null keys. Understanding these differences helps in choosing the right Map implementation e based on ordering and requirements. Thanks to my mentors for their guidance: Saketh Kallepu Anand Kumar Buddarapu Uppugundla Sairam Kishor Kumar #Java #HashMap #LinkedHashMap #TreeMap #JavaCollections #LearningJourney #Codegnan

💡 HashMap vs HashSet in Java Both are part of the Java Collection Framework but serve different purposes. 🔹 HashMap Stores data in key–value pairs. Each key must be unique. Example: {1 → "Java", 2 → "Spring"} 🔹 HashSet Stores only unique elements. No duplicate values allowed. Example: ["Java", "Spring", "SQL"] 📌 Simple way to remember: HashMap → Key + Value HashSet → Only Values #Java #JavaCollections #Programming #BackendDeveloper

Most Java developers use HashMap every day. But very few actually know how HashMap works internally. Here’s a simple visual explanation of how HashMap stores (put) and retrieves (get) data. #java #backenddevelopment #springboot #softwareengineering #datastructures

🚀 Moving Zeros to the End Using Java Streams I recently solved the classic “move zeros to the end” problem using a Java Streams approach, a bit different from the traditional two-pointer technique. The goal is simple: 👉 Move all zeros to the end 👉 Maintain the order of non-zero elements 🔹 Approach 1. Used Stream.concat() to concatenate two streams: 2. First stream, filters all non-zero elements 3. Second stream, filters all zero elements 4. Finally, collect the combined stream into a List. 💻 I’ve added my Java solution in the comments below. #Java #Java8 #Streams #Arrays #ProblemSolving #Coding

🚀 Java Interview Insight – Understanding HashMap Internals Most Java developers use HashMap daily… But very few truly understand how it works internally. 🔹 HashMap stores data in an array of buckets. 🔹 It uses the hashCode() of the key to calculate the index. 🔹 If multiple keys land in the same bucket, collision handling happens using LinkedList (Java 7) or balanced Tree (Java 8+). 🔹 When the load factor threshold is exceeded, resizing happens — which can impact performance. 💡 Why should you care? Because understanding this helps in writing better hashCode() methods, improving performance, and confidently answering interview questions. Backend development is not just about writing APIs — it’s about understanding what happens underneath. #Java #SpringBoot #Backend #InterviewPreparation

🚀 Strengthening My Java Fundamentals — ArrayList Example I recently practiced implementing ArrayList from the Java Collections Framework to better understand how dynamic data structures work in real-world applications. ✔️ Created and initialized an ArrayList ✔️ Added and accessed elements using index positions ✔️ Demonstrated flexible data handling compared to traditional arra Key takeaway 👉 Unlike arrays, ArrayList can grow dynamically, making it more flexible for real-world applications where data size is unpredictable. #Codegnan #Java #CollectionsFramework #CodingJourney #AnandKumarBuddarapu #SakethKallepu #UppugundlaSairam

Hello Java Developers, 🚀 Day 17 – Java Revision Series Today’s topic: Internal Working of TreeMap in Java 🌳 Unlike HashMap and LinkedHashMap, TreeMap stores keys in sorted order. 💡 Internally, TreeMap uses a Red-Black Tree (self-balancing BST). 🔹 How put(key, value) works: Compare key using compareTo() or Comparator Traverse left/right like a BST Insert node at correct position Rebalance the tree using rotations & recoloring 🔹 How get(key) works: Start from root Compare and move left/right Find the node in O(log n) time 🎯 Key points: Always sorted order Operations: O(log n) Supports range queries: subMap(), headMap(), tailMap() Slower than HashMap, but perfect when ordering matters 📄 I’ve shared a PDF with diagrams + step-by-step flow for quick revision. #Java #CoreJava #TreeMap #JavaInternals #DataStructures #InterviewPreparation #LearningInPublic

99% of Java Developers Use HashMap Every Day — But Don’t Know How It Actually Works | by Shanu Reddy | Mar, 2026 | Medium https://lnkd.in/gaacvBWR