Java JVM Execution Flow Explained

One Java mistake that cost us performance in production Early in my career, I thought: “The framework will handle performance.” I was wrong. In one production system, response times slowly increased under load. No errors. No crashes. Just slow. The mistake? 👉 Ignoring object creation and GC impact. We were: Creating unnecessary objects in hot paths Not understanding how GC pauses affected latency The fix: Reduced object creation Reused objects where possible Tuned JVM memory settings Result: 👉 ~30% improvement in response time. Lesson learned: Frameworks don’t replace understanding fundamentals. Java performance starts with knowing how the JVM behaves. What’s one performance issue you’ve faced in Java applications? #Java #JVM #BackendEngineering #Performance #SoftwareEngineering

### Java Custom Exception Internals Flow ### 1️⃣ Condition fails 2️⃣ Exception object created 3️⃣ Stored in Heap 4️⃣ throw breaks normal flow 5️⃣ JVM captures stack trace 6️⃣ catch handles or program crashes

You already know interfaces in Java. A Functional Interface is simply an interface with exactly one abstract method — nothing more. This constraint is intentional and it allows Java to represent behavior as a value. Runnable is a classic example. It defines a single contract: void run(); Because there is only one abstract method, the compiler can infer intent and accept a lambda as its implementation. Runnable task = () -> {   System.out.println("Executing task for Anwer Sayeed"); }; The lambda doesn’t replace Runnable. It implements its contract, concisely. This design choice is what enabled Java’s functional style without breaking its object-oriented foundations. #Java #FunctionalInterface #Runnable #LambdaExpressions #JavaDeveloper #CleanCode #Multithreading

One important lesson I’ve learned while working with Java applications: Memory issues can silently impact application performance. Some common mistakes developers make: • Creating too many unnecessary objects • Not closing database or stream resources • Improper caching strategies • Large collections staying in memory • Ignoring JVM monitoring and profiling These small issues can lead to: • High memory consumption • Garbage collection overhead • Application slowdowns • Even OutOfMemoryError in production A few good practices that help: ✔ Use try-with-resources to close resources properly ✔ Monitor JVM memory using tools like VisualVM or JConsole ✔ Avoid keeping large objects in memory unnecessarily ✔ Use caching carefully Sometimes performance problems are not about algorithms — they are about how efficiently memory is used. What tools do you use to monitor Java application performance? #Java #JVM #BackendDevelopment #SoftwareEngineering

💡 𝗝𝗮𝘃𝗮 𝗖𝗮𝘀𝘁𝗶𝗻𝗴: 𝗖𝗼𝗺𝗽𝗶𝗹𝗲-𝗧𝗶𝗺𝗲 𝘃𝘀 𝗥𝘂𝗻𝘁𝗶𝗺𝗲 𝗘𝘅𝗰𝗲𝗽𝘁𝗶𝗼𝗻𝘀 — 𝗘𝘅𝗽𝗹𝗮𝗶𝗻𝗲𝗱 𝗟𝗼𝗴𝗶𝗰𝗮𝗹𝗹𝘆 Many developers wonder why an invalid cast sometimes results in a ClassCastException at runtime, even when it looks obvious at compile time. The key reason: 👉 The 𝗰𝗼𝗺𝗽𝗶𝗹𝗲𝗿 𝗼𝗻𝗹𝘆 𝗸𝗻𝗼𝘄𝘀 𝘁𝗵𝗲 𝗿𝗲𝗳𝗲𝗿𝗲𝗻𝗰𝗲 𝘁𝘆𝗽𝗲, not the 𝗮𝗰𝘁𝘂𝗮𝗹 𝗼𝗯𝗷𝗲𝗰𝘁 𝘁𝘆𝗽𝗲 at compile time. Because of polymorphism, the compiler must assume that a subclass might exist that makes the cast valid—and therefore defers the decision to runtime. However, when you add stronger guarantees like final (or sealed classes), the compiler gains 𝗰𝗼𝗺𝗽𝗹𝗲𝘁𝗲 𝗰𝗲𝗿𝘁𝗮𝗶𝗻𝘁𝘆 and can reject the cast at 𝗰𝗼𝗺𝗽𝗶𝗹𝗲 𝘁𝗶𝗺𝗲. 📌 Takeaway: Java’s compiler is not dumb—it’s cautious. Give it enough information, and it becomes very smart. Understanding why this happens is far more powerful than memorizing rules. Check: https://lnkd.in/g88yhKev #Java #OOP #SoftwareEngineering #JavaConcepts #ClassCastException #LearningByUnderstanding

🔥 DAY 17 – Cleaner Java with Streams Java Streams make collection handling elegant. Example: List<String> names = users.stream() .map(User::getName) .collect(Collectors.toList()); Why use Streams? ✔ Less boilerplate ✔ Functional style ✔ Cleaner logic But don’t overuse it for complex logic. Readable > Fancy. #Java #CleanCode

Missed posting yesterday. Used the time to revise Java fundamentals. Revision in Java isn’t about rereading syntax. It’s about rediscovering why things work the way they do. Yesterday’s revision focused on: • How memory is managed inside the JVM • Why equals() matters beyond comparisons • How exceptions propagate through method calls • The real difference between == and .equals() These topics feel small — until they cause real bugs. Frameworks change. APIs evolve. But Java fundamentals stay relevant. Revising basics is not going backward. It’s upgrading how you think. Back today. Building on stronger foundations. #Java #CoreJava #JVM #BackendDevelopment #SoftwareEngineering #LearningInPublic #BuildInPublic

Very interesting to see that java applies Levenshtein edit distance algorithm for JVM XX flags options but not the java launcher options. Is something stopping us to do so ? jdk-25.jdk/Contents/Home/bin/java -XX:+TiereddCompilation Unrecognized VM option 'TiereddCompilation' Did you mean '(+/-)TieredCompilation'? Error: Could not create the Java Virtual Machine. Error: A fatal exception has occurred. Program will exit. YOU CAN CLEARLY SEE THE HELP. BUT HERE jdk-25.jdk/Contents/Home/bin/java -list-module Unrecognized option: -list-module Error: Could not create the Java Virtual Machine. Error: A fatal exception has occurred. Program will exit. YOU CAN"T SEE THE HELP. In the end, both are not able to create JVM, so even the launcher option can "help" us. #java25 #jdk25 #jvm #java

Java Fundamentals Series – Day 3 JVM Memory Model : JVM divides memory into 5 main areas to manage program execution efficiently: 1. Method Area Stores class metadata, method details, and static variables. 2. Heap Stores all objects and instance variables. 3. Stack Stores method calls, local variables, and references. 4. Program Counter (PC) Register Stores the address of the currently executing instruction. 5. Native Method Stack Used for execution of native (non-Java) methods. #Java #JVM #Backend developer #Computer science #Placements

>Why JVM Is the Heart of Java? When we say “Java is platform independent,” The Java Virtual Machine (JVM) is the engine that runs Java applications. It converts bytecode into machine-level instructions that the system understands. But JVM is more than just an executor 👇 >What Does JVM Consist Of? 1. Class Loader Subsystem Loads .class files into memory and verifies bytecode. 2. Runtime Data Areas (Memory Areas) Heap (Objects) Stack (Method calls & local variables) Method Area (Class metadata) PC Register Native Method Stack 3. Execution Engine Interpreter JIT (Just-In-Time) Compiler Garbage Collector 4. Garbage Collector (GC) Automatically manages memory by removing unused objects. >Why JVM Is Important? - Enables platform independence - Provides automatic memory management - Improves performance using JIT - Ensures security through bytecode verification - Manages multithreading efficiently Without JVM, Java wouldn’t be scalable, secure, or enterprise-ready. JVM is not just a runtime — it’s a complete execution environment. #JVM #Java #JavaDeveloper #BackendDevelopment #SoftwareEngineering #CoreJava #JavaInternals #GarbageCollection #JITCompiler #MemoryManagement #PlatformIndependent #Bytecode #Multithreading #HighPerformance #SystemDesign #SpringBoot #Microservices #Programming #Coding #TechLearning #DeveloperJourney #JavaCommunity