🏗️ Java Architecture

Understanding the Java Architecture is essential for grasping how Java programs are compiled, executed, and made platform-independent. It consists of several components that work together to run your Java application.

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🧱 Core Components of Java Architecture

Component	Description
📝 Source Code	You write your Java code in .java files using a text editor or IDE
🧮 Compiler (javac)	Converts .java source code into .class bytecode
📦 Bytecode	Intermediate, platform-independent code understood by the JVM
🧠 Java Virtual Machine (JVM)	Executes the bytecode and makes Java platform-independent
⚙️ Java Runtime Environment (JRE)	Provides the JVM + core libraries to run Java programs
🔧 Java Development Kit (JDK)	Contains the JRE + development tools (compiler, debugger, etc.)

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🔄 Java Program Execution Flow

1. Write your Java program: Hello.java

2. Compile it using javac Hello.java → generates Hello.class

3. Run it with java Hello → JVM loads and executes bytecode

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🔁 Step-by-Step Flow Diagram (Textual)

plaintext
.java file
   ↓ (compiled by javac)
.class file (bytecode)
   ↓ (interpreted/compiled by JVM)
Machine Code (runs on OS)

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☕ Java Virtual Machine (JVM)

• JVM is the engine that runs Java bytecode on your system.

• It performs:

  • Class loading

  • Bytecode verification

  • Memory management (Garbage Collection)

  • Just-In-Time (JIT) compilation

✅ JVM ensures your Java code runs anywhere with a compatible JVM—making it truly portable.

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📦 Java Runtime Environment (JRE)

• A package that includes:

  • JVM

  • Java class libraries

  • Other files required to run Java applications

You need JRE to run Java apps, but not to develop them.

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🛠️ Java Development Kit (JDK)

• A complete software development package containing:

  • JRE

  • Compiler (javac)

  • Debugger (jdb)

  • Other dev tools

You need JDK to write, compile, and debug Java programs.

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🧠 Summary Table

Component	Role
.java File	Human-readable source code
javac	Compiles code into bytecode
.class File	Platform-independent bytecode
JVM	Runs the bytecode
JRE	JVM + libraries to run code
JDK	JRE + tools to write and compile code