Java Introduction

What is Java?

Java is a high-level, class-based, object-oriented programming language designed to be portable, secure, and maintainable for long-term software development.

It follows the principle:

Write Once, Run Anywhere (WORA)

Java code is compiled into bytecode, which runs on the Java Virtual Machine (JVM) — making it platform-independent.

Key Characteristics

• Platform independent: Java code compiles into bytecode that runs on the JVM, so the same program can run on Windows, Linux, or macOS.
• Strongly typed + OOP-friendly: Encourages clear structure (classes, interfaces) and safer refactoring.
• Rich ecosystem: Mature standard library + huge community + frameworks (e.g., Spring) and build tools (Maven/Gradle).
• Performance: The JVM uses JIT compilation to optimize frequently executed code paths.

Quick Facts

• Developed by Sun Microsystems (1995) (now Oracle)
• Syntax inspired by C/C++, but safer
• Widely used in:
  • Backend development
  • Android apps
  • Enterprise systems
  • Cloud & distributed systems

Why We Need Java?

Java became popular because it solves major problems developers faced earlier:

Reasons to Use Java

1. Platform Independence No need to rewrite code for different systems
2. Stability & Reliability Used in banking, enterprise, and critical systems
3. Security Built-in features like bytecode verification and sandboxing
4. Large Ecosystem Frameworks like Spring, Hibernate
5. Scalability Handles large applications easily
6. Job Opportunities Huge demand in backend and enterprise development

History of Java

Java was created by James Gosling and his team at Sun Microsystems.

Timeline

• 1991 → Project started (called Oak)
• 1995 → Renamed to Java and officially released
• 1996 → First public version (JDK 1.0)
• 2009 → Oracle acquired Sun Microsystems
• 2014 → Java 8 (most popular release)
• 2021+ → Modern LTS versions (Java 17, 21)

Why Learn Java?

1. Widely Used and In-Demand Java is used by millions of developers and powers everything from enterprise applications to Android apps and web services. Top companies like Google, Netflix, and Amazon rely on it.

2. Beginner-Friendly, Yet Powerful Java has a clean, readable syntax and a vast ecosystem of tools and libraries. It’s great for beginners but also scales well for advanced projects.

3. Write Once, Run Anywhere Java is platform-independent. You write code once and run it on any system with a Java Virtual Machine (JVM).

4. Robust and Secure With strong memory management, type safety, and built-in security features, Java is ideal for building reliable and secure applications.

5. Career and Job Opportunities Java developers are always in demand — especially in backend development, enterprise systems, and Android app development.

6. Strong Foundation for Other Tech Learning Java helps you understand key concepts like OOP (Object-Oriented Programming), multithreading, and data structures — which are useful in many other languages too.

Types of Java Applications

Java is used to build different types of applications:

1. Web Applications: Backend APIs using frameworks like Spring Boot Example: E-commerce websites
2. Mobile Applications: Android apps (Java/Kotlin)
3. Enterprise Applications: Banking systems, ERP, CRM Highly scalable and secure
4. Cloud-Based Applications: Microservices and distributed systems
5. Big Data Applications: Tools like Hadoop, Spark run on JVM
6. Desktop Applications: GUI apps using JavaFX, Swing

Java Versions History

Version	Release Date	Key Features / Notes
JDK 1.0	January 1996	Initial release — basic core API and JVM
JDK 1.1	February 1997	Inner classes, JDBC, RMI, JavaBeans
J2SE 1.2	December 1998	Collections framework, Swing, JIT compiler
J2SE 1.3	May 2000	HotSpot JVM, RMI over IIOP
J2SE 1.4	February 2002	assert keyword, NIO, logging API, XML parsing
Java SE 5	September 2004	Generics, enhanced for-loop, annotations, enums, autoboxing
Java SE 6	December 2006	Scripting engine (JS), improvements in Web Services, JVM monitoring
Java SE 7	July 2011	try-with-resources, NIO.2, Diamond operator
Java SE 8	March 2014	Lambda expressions, Streams API, Optional, Date/Time API
Java SE 9	September 2017	JPMS (modules), JShell, improved JDK structure
Java SE 10	March 2018	var for local variable type inference
Java SE 11	September 2018	LTS version, removed JavaFX, HTTP Client API
Java SE 12	March 2019	Switch expressions (preview)
Java SE 13	September 2019	Text blocks (preview), dynamic CDS
Java SE 14	March 2020	Records (preview), instanceof pattern matching (preview)
Java SE 15	September 2020	Sealed classes (preview), hidden classes
Java SE 16	March 2021	Records and pattern matching (finalized), new memory APIs
Java SE 17	September 2021	LTS version, sealed classes, pattern matching
Java SE 18	March 2022	Simple web server, UTF-8 by default
Java SE 19	September 2022	Virtual threads (preview), structured concurrency (preview)
Java SE 20	March 2023	Continued virtual threads and pattern matching enhancements
Java SE 21	September 2023	LTS version, virtual threads, string templates, sequenced collections
Java SE 22	March 2024	Unnamed classes, class-file API improvements (preview)

Java Program Structure

Here’s a simple Hello World program:

publicclassHelloWorld {
   publicstaticvoidmain(String[]args) {
      System.out.println("Hello, World!");
   }
}

Explanation

• class HelloWorld → Defines a class
• main() method → Entry point of the program
• System.out.println() → Prints output

Execution Flow

1. Write code → .java file
2. Compile → Bytecode (.class)
3. Run using JVM