Corporate Training Study
Material: Java Virtual Machine (JVM) Architecture
📌 Session Title: Java
Virtual Machine (JVM) Architecture
- Duration:
1 Hour
- Audience:
Corporate Employees, Software Developers, Java Beginners
- Learning
Objectives:
✅ Understand the role of JVM, JRE, and JDK
✅ Learn how Java code is compiled and executed
✅ Deep dive into JVM architecture and its components
📖 Module 1: Introduction
to Java Virtual Machine (JVM)
1.1 What is JVM?
📌 JVM (Java Virtual Machine) is
an abstract machine that enables Java programs to run on any device or
operating system. It is responsible for:
✔ Converting Java bytecode
into machine code
✔ Managing memory
allocation & garbage collection
✔ Ensuring Java follows
its "Write Once, Run Anywhere" principle
📌 JVM is platform-dependent, but
Java code is platform-independent.
📖 Module 2: Understanding
JDK, JRE, and JVM
2.1 JDK (Java Development
Kit)
✔ A development environment to
write, compile, and run Java applications.
✔ Includes JRE +
Compiler + Debugging Tools
✔ Used by developers for
Java application development.
✅ JDK Components:
- javac
→ Java Compiler
- java
→ Java Application Launcher
- javadoc
→ Java Documentation Tool
- jar
→ Java Archive Utility
📌 Popular JDKs: Oracle JDK,
OpenJDK, Amazon Corretto, IBM JDK
2.2 JRE (Java Runtime
Environment)
✔ A runtime environment to execute
Java programs.
✔ Includes JVM + Core
Java Libraries.
✔ Used by end-users to run
Java applications (e.g., Web browsers with Java Applets).
✅ JRE Components:
- JVM
(Java Virtual Machine) → Converts bytecode to machine
code.
- Core
Libraries → Java APIs like java.lang, java.io,
etc.
- Runtime
Libraries → Required dependencies to run Java
programs.
📌 If you only need to run Java
applications, install JRE.
2.3 JVM (Java Virtual
Machine)
✔ The heart of Java responsible for
executing Java bytecode.
✔ Converts .class files
(bytecode) into machine code.
✔ Manages memory
allocation & garbage collection.
✅ JVM Components:
- Class
Loader → Loads .class files
- Memory
Area → Heap, Stack, Method Area, PC Register
- Execution
Engine → Converts bytecode into native
machine code
- Garbage
Collector → Frees unused memory
📌 JVM is platform-dependent, but
Java bytecode runs on any JVM.
📖 Module 3: JVM
Architecture - How Java Code is Compiled and Executed
3.1 Java Compilation and
Execution Process
🔹 Step 1: Write a Java Program
(Hello.java)
public class Hello {
public static void main(String[] args) {
System.out.println("Hello,
World!");
}
}
🔹 Step 2: Compile Java Code
javac Hello.java
✔ The javac compiler converts Hello.java to
Hello.class (bytecode).
🔹 Step 3: Run Java Bytecode
java Hello
✔ The JVM reads Hello.class and
executes it on the machine.
📌 Key Point: Java runs in two
steps – Compilation (to bytecode) and Execution (by JVM).
3.2 JVM Internal
Architecture (Detailed Breakdown)
🛠 1. Class Loader Subsystem
✔ Loads Java classes into
memory (.class files).
✔ Performs Bytecode
Verification for security.
✔ Uses three class
loaders:
- Bootstrap
Class Loader (Loads core Java classes, e.g., java.lang.*).
- Extension
Class Loader (Loads Java extension libraries,
e.g., javax.crypto).
- Application
Class Loader (Loads user-defined classes).
🛠 2. Runtime Memory Areas (JVM
Memory Model)
📌 JVM divides memory into different
sections:
|
Memory Area |
Purpose |
|
Method Area |
Stores class metadata,
method bytecode, static variables. |
|
Heap Memory |
Stores objects and
class instances. |
|
Stack Memory |
Stores method call
stack, local variables. |
|
PC Register |
Stores memory address
of the executing instruction. |
|
Native Method Stack |
Handles OS-specific
native code execution. |
🛠 3. Execution Engine
✔ Converts Java bytecode
to native machine code.
✔ Uses Just-In-Time
(JIT) Compiler for performance optimization.
📌 JIT Compiler (Just-In-Time)
- Improves
speed by compiling frequently used bytecode into
machine code.
- Uses
techniques like Method Inlining, Loop Unrolling, Dead Code Elimination.
🛠 4. Garbage Collection (Memory
Management)
✔ JVM automatically
reclaims unused memory using Garbage Collection (GC).
✔ Types of GC
Algorithms:
- Serial
GC (Single-threaded, for small apps).
- Parallel
GC (Multi-threaded, for performance).
- G1
GC (Advanced, for large-scale applications).
- ZGC
& Shenandoah GC (Low-latency garbage
collectors).
📌 Best Practice: Always release
unused objects to avoid memory leaks.
📖 Module 4: JVM
Performance Tuning & Optimization
4.1 JVM Tuning Parameters
✅ Use JVM options to monitor &
optimize performance:
java -Xms512m -Xmx1024m -XX:+UseG1GC -XX:+PrintGCDetails
✔ -Xms → Initial heap size
✔ -Xmx → Maximum heap size
✔ -XX:+UseG1GC → Enable G1
Garbage Collector
✔ -XX:+PrintGCDetails →
Show garbage collection logs
📖 Module 5: Hands-on Lab
& Practical Session
✅ Demo 1: Installing and Configuring JDK
✔ Install JDK, set JAVA_HOME,
and configure PATH.
✅ Demo 2: Writing & Running a Java
Program
✔ Compile & execute
Java code using javac and java commands.
✅ Demo 3: Debugging JVM Memory Usage
✔ Use jconsole and VisualVM
to monitor JVM performance.
📖 Summary: Key Takeaways
✔ JVM is the runtime engine that
executes Java bytecode.
✔ JRE provides
runtime libraries, while JDK includes tools for development.
✔ JVM consists of Class
Loader, Runtime Memory, Execution Engine, and Garbage Collector.
✔ Java code is compiled
to bytecode and executed by JVM using Just-In-Time (JIT) compilation.
✔ Garbage Collection
(GC) manages memory efficiently and prevents memory leaks.
📌 "Write Once, Run
Anywhere" is possible because Java runs on JVM!
