What is a Lambda Expression in Java?

🧭 Day 16: Iterating Through ArrayList in Java Today, I learned different ways to loop through an ArrayList — each method gives flexibility based on what you need. 💡 What I Learned Today For Loop – Access elements using index. Enhanced For Loop (for-each) – Simple and clean way to read data. Iterator – Best when you want to remove elements while looping. ListIterator – Can iterate both forward and backward. forEach() Method – Uses lambda expressions for modern Java style. 🧩 Example Code import java.util.*; public class IterateArrayList {   public static void main(String[] args) {     ArrayList<String> names = new ArrayList<>();     names.add("Raj");     names.add("Arun");     names.add("Kumar");     // For loop     for (int i = 0; i < names.size(); i++)       System.out.println("For Loop: " + names.get(i));     // For-each loop     for (String name : names)       System.out.println("For-each: " + name);     // Iterator     Iterator<String> it = names.iterator();     while (it.hasNext())       System.out.println("Iterator: " + it.next());     // forEach method     names.forEach(n -> System.out.println("Lambda: " + n));   } } 🗣️ LinkedIn Caption 🔁 Day 16 – Iterating through ArrayList in Java Today I explored 5 powerful ways to loop through ArrayLists — from classic for-loops to modern lambdas. Each method offers unique control and flexibility when working with lists. #Java #CoreJava #ArrayList #LearnJava #Programming

Day 90 of #100DaysOfCode Solved Squares of a Sorted Array in Java 🔠 Approach The task was to take an array of integers sorted in non-decreasing order, square each number, and then return the result array also sorted in non-decreasing order. Brute-Force Method The solution implemented here is a straightforward two-step brute-force approach: Squaring: I iterated through the input array nums and replaced each element with its square (i.e., nums[i] * nums[i]). This handles both positive and negative numbers correctly. Sorting: After squaring all elements, I used Java's built-in Arrays.sort(nums) method to sort the entire array. While correct, this approach has a time complexity dominated by the sorting step, which is O(NlogN), where N is the number of elements. The runtime of 10 ms shows that a more efficient, two-pointer approach (which can solve this in O(N) time) is generally preferred for optimal performance. #Java #100DaysOfCode #LeetCode #CodingChallenge #Algorithms #Array #Sorting #ProblemSolving

🚀 Day 76: Numerically Balanced Brute Force – Java Edition Today’s challenge was deceptively simple yet oddly satisfying: 🔢 Find the next numerically balanced number greater than a given integer. A number is numerically balanced if every digit d appears exactly d times. Examples: 22 → two 2s ✅ 1333 → one 1, three 3s ✅ 122 → one 1, two 2s ❌ (2 appears only once) I went full brute-force in Java, and it worked like a charm: java public int nextBeautifulNumber(int n) { for (int i = n + 1; i <= 1224444; i++) { if (isBalanced(i)) return i; } return -1; } private boolean isBalanced(int num) { int[] count = new int[10]; int temp = num; while (temp > 0) { count[temp % 10]++; temp /= 10; } for (int i = 0; i < 10; i++) { if (count[i] != 0 && count[i] != i) return false; } return true; } 🧠 Clean logic, no fancy tricks. Just a solid loop and a digit frequency check. 📌 Lesson: Sometimes brute force is enough—if you know your bounds and keep it clean. Let me know if you’ve tackled this one differently or optimized it further. #100DaysOfCode #Java #LeetCode #ProblemSolving #NumericallyBalanced #CodingJourney #Day76

Today I worked on the problem "Convert Sorted List to Binary Search Tree" in Java — a perfect blend of Linked List and Tree logic! 🌳 🔍 Key Concepts Covered: Finding the middle element of a Linked List using the slow & fast pointer approach Recursively constructing a height-balanced BST Strengthening understanding of Divide and Conquer strategies This problem really sharpened my thinking around recursive structures and pointer management — small yet powerful steps toward writing more efficient and elegant Java code. 💻✨ 💬 What’s your favorite data structure to work with — Linked Lists or Trees? #LeetCode #Java #DataStructures #Algorithms #CodingJourney #LearningEveryday #ProblemSolving #SoftwareEngineering

Day 88 of #100DaysOfCode Solved Decrypt String from Alphabet to Integer Mapping in Java 🔡 Approach Today's challenge involved mapping a string of digits to lowercase English characters, where single digits '1' through '9' map to 'a' through 'i', and two digits followed by a '#' (e.g., '10#', '11#') map to 'j' through 'z'. I used an iterative approach with a while loop and an index i to traverse the input string. I checked ahead to see if a two-digit mapping existed by looking for a '#' at s.charAt(i + 2). If a '#' was found, I parsed the two-digit number (e.g., "10", "11") using s.substring(i, i + 2), converted it to an integer, and then mapped it to the correct character by adding it to the ASCII value of 'a' and subtracting one. I then advanced the index i by 3. If no '#' was found, it meant the current character s.charAt(i) was a single-digit mapping. I converted this digit to an integer and mapped it to a character similarly, then advanced the index i by 1. This approach processes the string from left to right, correctly handling the two-digit encodings first, which resulted in a quick runtime that beat 79.30% of other submissions. #Java #100DaysOfCode #LeetCode #CodingChallenge #Algorithms #StringManipulation #ProblemSolving

Understanding Method Overloading & Method Overriding in Java 💡 Both concepts seem similar — but they’re not! Here’s the difference 👇 🔹 Method Overloading (Compile-Time Polymorphism) ➡️ Same method name, different parameters ➡️ Happens within the same class ➡️ Resolved at compile time class Calculator { int add(int a, int b) { return a + b; } double add(double a, double b) { return a + b; } // Overloaded } 📘 Use when you want flexibility with inputs but same logic. 🔹 Method Overriding (Runtime Polymorphism) ➡️ Same method name & parameters ➡️ Happens in subclass ➡️ Resolved at runtime class Animal { void sound() { System.out.println("Animal sound"); } } class Dog extends Animal { @Override void sound() { System.out.println("Bark"); } } 📘 Use when a child class modifies parent behavior. 🔑 Key Takeaways ✅ Overloading → same method name, different parameters ✅ Overriding → same method signature, different behavior ✅ Overloading = Compile-time | Overriding = Runtime ✨ #Java #OOPs #MethodOverloading #MethodOverriding #JavaLearning

💡A method is a function that settled down , inside a class, or wherever belonging felt right. Most languages let you write free-floating functions, but Java doesn’t really have them. The Java Language Specification (JLS) never even uses the word “function.” Instead, it uses the word “method” - behavior that must always belong to something. That’s why in Java you can’t just write println("Hello, World"); Every piece of behavior needs a home, System.out.println("Hello, World"); Or in newer versions such as Java 25, IO.println("Hello, World"); It still belongs to something - a class, an object, or a type reference. 🏠 However, with java.util.function, Java introduced a new way to act functional without ever changing its true nature. These aren’t real functions; they’re functional interfaces, single-method contracts. 🧾 When you write a lambda like x -> x * 2 you’re not creating a standalone function , you’re creating an object that behaves like one. The JVM quietly builds a lightweight instance that points to an underlying method, keeping it anchored in Java’s object-oriented structure. #Java #Programming #Coding #ObjectOriented #SoftwareDevelopment #TechExplained #LearnJava #CodingLife

⚙️ Deep Dive into Java Interfaces, Exception Handling, and Collections Framework Ever wondered how Java manages polymorphism, abstraction, and safe error handling — all while keeping performance in check? 🤔 That’s exactly what I explored this week while learning Java in depth. Here’s a quick breakdown of what I learned 👇 💥 1️⃣ Exception Handling — Writing Robust Code Learned about throw, throws, and the difference between checked & unchecked exceptions. Explored how try, catch, and finally blocks work under the hood. Understood how Java ensures program stability even when errors occur. 📚 2️⃣ Collections Framework — Efficient Data Management Understood why Java Collections are used instead of arrays. Studied the time complexity and internal working of List, Set, and Map. Learned how data structures like HashMap, LinkedHashSet, and ArrayList are implemented internally. 🧩 3️⃣ Interfaces — The Power of Abstraction Understood how interfaces help achieve polymorphism and multiple inheritance in Java. Learned that interfaces can extend other interfaces but cannot implement them. Explored default methods (Java 8+), which allow method bodies inside interfaces. Attached my handwritten summary 📸 for a quick glance at these key interface concepts. 🚀 Takeaway: Understanding these topics gave me deeper insight into how Java ensures modularity, flexibility, and runtime efficiency — the backbone of backend development. #Java #BackendDevelopment #LearningJourney #JavaDeveloper #ExceptionHandling #CollectionsFramework #Interface #OOP #SpringBoot #CodingJourney #SoftwareDevelopment #TechLearning

𝐓𝐨𝐩 𝐉𝐚𝐯𝐚 𝐕𝐢𝐫𝐭𝐮𝐚𝐥 𝐓𝐡𝐫𝐞𝐚𝐝𝐬 𝐈𝐧𝐭𝐞𝐫𝐯𝐢𝐞𝐰 𝐐𝐮𝐞𝐬𝐭𝐢𝐨𝐧𝐬 (2025) If you're preparing for Java interviews or brushing up on Project Loom, here are the MOST asked Virtual Threads questions you should master: ✅ 𝐓𝐨𝐩 𝐕𝐢𝐫𝐭𝐮𝐚𝐥 𝐓𝐡𝐫𝐞𝐚𝐝𝐬 𝐈𝐧𝐭𝐞𝐫𝐯𝐢𝐞𝐰 𝐐𝐮𝐞𝐬𝐭𝐢𝐨𝐧𝐬 1. What are Virtual Threads in Java? 2. Why were Virtual Threads introduced in Java? 3. How do Virtual Threads differ from Platform Threads? 4. What problem do Virtual Threads solve? 5. In which Java version did Virtual Threads become a stable feature? 6. Are Virtual Threads suitable for CPU-bound or I/O-bound tasks? 7. How do Virtual Threads improve scalability? 8. How does the JVM schedule Virtual Threads? 9. What happens when a Virtual Thread performs a blocking I/O operation? 10. What is the role of carrier threads in Virtual Threads? 11. How do Virtual Threads reduce memory usage? 12. Can we create millions of Virtual Threads? Why? 13. How do you create a Virtual Thread in Java? 14. What is 𝐓𝐡𝐫𝐞𝐚𝐝.𝐨𝐟𝐕𝐢𝐫𝐭𝐮𝐚𝐥() used for? 15. What is 𝐄𝐱𝐞𝐜𝐮𝐭𝐨𝐫𝐬.𝐧𝐞𝐰𝐕𝐢𝐫𝐭𝐮𝐚𝐥𝐓𝐡𝐫𝐞𝐚𝐝𝐏𝐞𝐫𝐓𝐚𝐬𝐤𝐄𝐱𝐞𝐜𝐮𝐭𝐨𝐫()? 16. Do Virtual Threads eliminate the need for thread pools? 17. What is structured concurrency in Project Loom? 18. How do Virtual Threads integrate with Executors? 19. What are the limitations of Virtual Threads? 20. What happens if a Virtual Thread enters a long synchronized block? 21. Are Virtual Threads preemptive or cooperative? 22. Do existing Java libraries need to change to support Virtual Threads? 23. How do Virtual Threads help in designing scalable servers? 24. Can Virtual Threads run on multiple CPU cores? 25. How do Virtual Threads handle blocking JDBC calls? 26. What challenges might occur when using Virtual Threads with legacy code? 27. How do Virtual Threads compare to Kotlin coroutines or Go goroutines? 28. What is pinning in the context of Virtual Threads? 29. How do Virtual Threads interact with locks and synchronization? 30. Can Virtual Threads be debugged like normal threads? If you found this helpful, follow Madhu K. for more Java, Spring Boot, and backend interview content #Java #SpringBoot #VirtualThreads #ProjectLoom #BackendDevelopment #InterviewPrep #CodingMadeSimple #MadhuKumari #BiharGeeks

👉 Why should a Functional Interface contain only one abstract method? 📌 Ex - interface Interf { public void m1(int i) } Interf I = i -> System.out.println(i * i); I.m1(10); I.m2(20); 👉 A functional interface must have exactly one abstract method because a lambda expression is meant to represent a single functionality or behavior. When you write a lambda expression, it needs to map to one specific abstract method in the interface. If the interface had multiple abstract methods, the compiler wouldn’t know which method the lambda is referring to — leading to ambiguity. That’s why a functional interface can have only one abstract method, and it is the only type of interface that can be used with lambda expressions in Java. 👉 Why can’t a Functional Interface have two abstract methods? 📌 Ex - interface Interf { public void m1(int i); public void m2(int i); } Interf I = i -> System.out.println(i * i); 💡Compile Time Error - Interf is not a Functional Interface - Multiple non-overriding abstract method in interface Interf 👉 If an interface contains two abstract methods, a lambda expression won’t know which method to map to, because there are multiple choices. That’s why a Functional Interface must contain exactly one abstract method this ensures that the lambda expression can clearly represent that single method. #OOP #Abstraction #CleanCode #LearningJava #Programming #Developers #String #CodingTips #CoreJava #Learning #JavaDeveloper #CodingPractice #Interface #JavaInterviewPreparation #LearnToCode #JavaInterviewPreparation #JavaFresher #Java #Java8 #FunctionalInterface #LambdaExpressions