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The get() method in HashMap is one of the most commonly used operations. Although it looks like a simple key lookup, internally it involves hashing, bucket indexing, and collision handling. In this article, we’ll break down the internal working of HashMap.get() step by step with examples. 1. Hashing the Key When you call map.get(key) , the HashMap computes a hash value using the key’s hashCode() . In Java 8+, this value is further processed with bitwise operations to spread the hash bits and reduce collisions. int hash = hash(key.hashCode()); 2. Finding the Bucket The hash value is then converted into an index in the internal array (called table ) using: int index = (n - 1) & hash; // n = table.length This determines the bucket where the entry might be stored. 3. Searching Inside the Bucket Each bucket can contain: null → no entry stored A single key-value pair A linked list of nodes (if multiple keys hash to the same bucket) A red-blac...

Introduction: System design can feel overwhelming — especially when vast topics like scalability, performance, reliability, and distributed architecture are thrown at you all at once. But once you master the foundational building blocks, designing robust and scalable systems transforms from stressful to doable. In this post, we’ll explore 30 essential system design concepts with explanation 1. Client–Server Architecture What it is: The foundational model: thin clients (browsers, mobiles, IoT) make requests; servers process logic and return responses. Servers can be single or a pool of machines. Why it matters: It separates concerns — UIs live in clients and heavy computation/state in servers — enabling centralized control, security, and shared business logic. Trade-offs & details: Clients must handle availability issues and degraded connectivity. This model fits web apps, but for extreme scale you need caching, CDNs, and stateless servers (see Diag...

In Java interviews, one of the most common topics you’ll encounter is object persistence —how Java objects are saved, transferred, and reconstructed. This is where concepts like Serialization , Deserialization , and Externalization come into play. These aren’t just theoretical ideas; they are crucial in distributed systems, caching, session management, and inter-process communication . Let’s explore these concepts step by step, highlight their differences, and discuss real-world use cases. 1. What is Serialization in Java? Serialization is the process of converting a Java object into a byte stream so that it can be stored in a file, transmitted over a network, or persisted in a database. How it works: The class must implement the Serializable interface (marker interface). Use ObjectOutputStream.writeObject() to serialize an object. Non-transient, non-static fields are serialized; transient fields are skipped. ...