Java Introduction

Java Introduction

Java is one of the most popular and widely used programming languages in the world. It is used for developing desktop applications, web applications, mobile apps (Android), games, cloud systems, enterprise software, and more.

What is Java?

Java is:

• Object-Oriented

• Platform Independent

• High-Level

• Secure

• Robust and Reliable

• Distributed and Multithreaded

Java was created by James Gosling at Sun Microsystems in 1995 (now owned by Oracle).

Why is Java so Popular?

 Main Components of Java Architecture

1. Java Source Code

• Written by the programmer in a .java file.

2. Java Compiler (javac)

• Converts source code into bytecode.

• Output file: .class

• Bytecode is platform-independent.

3. JVM (Java Virtual Machine)

The JVM is the core of Java architecture. It executes bytecode by converting it into machine code.

Internal components of JVM:

• Class Loader – Loads class files into memory.

• Bytecode Verifier – Checks code for security and correctness.

• Execution Engine

  • Interpreter (executes bytecode line by line)

  • JIT Compiler (improves performance by compiling to native code)

• Garbage Collector – Automatically removes unused objects from memory.

4. JRE (Java Runtime Environment)

• Provides the environment to run Java programs.

• Includes JVM and core libraries.

5. JDK (Java Development Kit)

• Used to develop Java applications.

• Includes JRE plus development tools like compiler, debugger, and documentation tools.

Java follows this cycle:

Java Program Structure (Example)

Explanation:

• class Hello → Defines a class named Hello.

• public static void main(String[] args) → Starting point of the program.

• System.out.println() → Prints text on the screen.

Java Applications

It used in:

• Android Apps

• Web Applications

• Enterprise Software (Banking, ERP)

• Cloud Computing

• Game Development

• IoT Devices

• Artificial Intelligence & Machine Learning (with Java libraries)

Java Editions

It is divided into different editions, each designed for a specific type of application.

Java SE (Java Standard Edition)

Purpose: Core Java programming

Used for:

• Desktop applications

• Basic web applications

• Learning Java fundamentals

Key Features:

• Core libraries (java.lang, java.util, java.io, etc.)

• Object-Oriented Programming

• Multithreading

• Exception Handling

• Networking

• JDBC (Database connectivity)

 This is the foundation of all other Java editions.

 Java EE (Java Enterprise Edition)

(Now known as Jakarta EE)

Purpose: Large-scale, enterprise-level applications

Used for:

• Enterprise web applications

• Banking systems

• E-commerce platforms

• Distributed systems

Key Features:

• Servlets

• JSP (Java Server Pages)

• EJB (Enterprise JavaBeans)

• JPA (Java Persistence API)

• Web Services (REST, SOAP)

• Security & Transactions

 Built on top of Java SE.

 Java ME (Java Micro Edition)

Purpose: Resource-constrained devices

Used for:

• Mobile phones (older devices)

• Embedded systems

• IoT devices

• Set-top boxes

Key Features:

• Lightweight APIs

• Small memory footprint

• Device-specific configurations

 Designed for devices with limited memory and processing power.

 Comparison Table

Key Concepts in Java

• Variables and Data Types

• Operators

• Control Statements (if, for, while)

• Methods and Functions

• OOP Concepts (Class, Object, Inheritance, Polymorphism, Encapsulation, Abstraction)

• Exception Handling

• Collections Framework

• Multithreading

• File Handling

• JDBC (Database Connectivity)

Advantages of Java

• Easy to learn

• Platform-Independent

• Community Support

• Secure and Stable

• Powerful for enterprise and web development

Disadvantages of Java

• Uses more memory compared to languages like C/C++

• Slightly slower because of JVM overhead

Who Uses Java? (Top Companies)

• Google

• Amazon

• Netflix

• LinkedIn

• Uber

• Instagram

• Spotify

• Oracle