High-Level Java Architecture Flow

The execution of a Java program follows these steps:

1. Write Java source code (.java)

2. Compile using JDK compiler (javac) → generates bytecode (.class)

3. Bytecode is loaded into JVM

4. JVM converts bytecode into machine code

5. Program output is displayed

Main Components of Java Architecture

Java Architecture mainly consists of:

1. JDK (Java Development Kit)

2. JRE (Java Runtime Environment)

3. JVM (Java Virtual Machine)

Let’s understand each component in detail.

1. Java Development Kit (JDK)

JDK is used by developers to create Java applications.

JDK includes:

• JRE

• Java compiler (javac)

• Debugger

• Development tools

Purpose of JDK:

• Write Java programs

• Compile source code

• Run Java applications

👉 Without JDK, Java development is not possible.

2. Java Runtime Environment (JRE)

JRE provides the environment required to run Java applications.

JRE includes:

• JVM

• Core Java libraries

• Supporting runtime files

Purpose of JRE:

• Execute Java programs

• Provide necessary class libraries

📌 JRE cannot compile code, it can only run Java applications.

3. Java Virtual Machine (JVM)

JVM is the heart of Java Architecture. It executes Java bytecode and makes Java platform independent.

Key responsibilities of JVM:

• Loads bytecode

• Verifies code for security

• Executes instructions

• Manages memory

• Handles garbage collection

📌 JVM is platform dependent, but Java bytecode is platform independent.

Internal Architecture of JVM

JVM consists of three main parts:

1. Class Loader Subsystem

2. Runtime Data Areas (Memory)

3. Execution Engine

1. Class Loader Subsystem

The Class Loader loads .class files into JVM memory.

Types of Class Loaders:

• Bootstrap Class Loader – loads core Java classes

• Extension Class Loader – loads extension classes

• Application Class Loader – loads application classes

Before execution, JVM verifies bytecode to ensure security.

2. Runtime Data Areas (JVM Memory)

These are memory areas used during program execution.

Main memory areas:

• Method Area – stores class-level data

• Heap Area – stores objects and instance variables

• Stack Area – stores method calls and local variables

• PC Register – stores current instruction

• Native Method Stack – supports native methods

3. Execution Engine

Execution Engine executes the bytecode.

Components:

• Interpreter – executes bytecode line by line

• JIT Compiler – converts bytecode into machine code

• Garbage Collector – removes unused objects

Why Java Architecture Is Platform Independent

Java Architecture uses JVM as an abstraction layer between Java programs and the operating system.

• Same bytecode runs on different OS

• JVM converts bytecode into OS-specific machine code

• No need to rewrite Java programs

This makes Java portable and flexible.

Advantages of Java Architecture

• Platform independent

• Secure execution environment

• Efficient memory management

• High performance with JIT

• Robust and reliable execution

Where Java Architecture Is Used

Java Architecture is used in:

• Web applications

• Android development

• Enterprise systems

• Cloud applications

• Big data platforms