Java topics from basics to advanced

🟢 Beginner (Core Java Basics)

✅ 1. Java Fundamentals

History of Java, Features

🕰️ History of Java

Year	Milestone
1991	Java was initiated by James Gosling, Mike Sheridan, and Patrick Naughton at Sun Microsystems as part of the Green Project. Initially named Oak.
1995	Oak was renamed to Java (inspired by Java coffee). Officially launched by Sun Microsystems.
1996	Java 1.0 released. "Write Once, Run Anywhere" (WORA) became the key slogan.
2006	Sun made Java open-source by releasing most of its source code under the GNU General Public License (GPL).
2009	Oracle Corporation acquired Sun Microsystems, taking over Java development.
2014 – Present	Java moved to a 6-month release cycle (starting from Java 9). Latest stable version as of August 2025 is Java 22 (released March 2025).

🌟 Core Features of Java

Feature	Description
1. Simple	Easy to learn, write, and debug. Follows C/C++ style but removes complex parts like pointers.
2. Object-Oriented	Everything is treated as an object. Encourages modular and reusable code.
3. Platform-Independent	Java code is compiled into bytecode which runs on the Java Virtual Machine (JVM). Enables "Write Once, Run Anywhere".
4. Secure	Java provides a runtime environment that doesn’t allow unauthorized memory access, supports encryption, and has a built-in security manager.
5. Robust	Strong memory management, exception handling, garbage collection, and compile-time checking.
6. Multithreaded	Built-in support for multithreaded programming (e.g., using `Thread`, `Runnable`, `ExecutorService`).
7. Distributed	Java supports networking and distributed computing (e.g., RMI, sockets).
8. High Performance	Though not as fast as C/C++, Java’s performance is improved via Just-In-Time (JIT) compiler.
9. Architecture-Neutral	Java bytecode is not specific to any processor, making Java architecture-neutral.
10. Dynamic	Java can dynamically load classes at runtime. It supports reflection and runtime type identification.

JVM, JRE, JDK

☕ JDK vs JRE vs JVM

Component	Full Form	What It Is	Purpose
JVM	Java Virtual Machine	A virtual machine that runs Java bytecode	Runs Java programs
JRE	Java Runtime Environment	JVM + libraries + tools needed to run Java programs	Environment to run Java
JDK	Java Development Kit	JRE + compilers + development tools	Toolkit to develop Java

🔧 1. JVM (Java Virtual Machine)

It’s a virtual engine that executes Java bytecode (.class files).
Platform-dependent: JVM is available for Windows, Linux, Mac, etc.
Key tasks:
- Loads class files
- Verifies bytecode
- Executes bytecode (via Interpreter or JIT Compiler)
- Handles memory (via Garbage Collector)

📌 Note: JVM is the heart of Java’s platform independence.

📦 2. JRE (Java Runtime Environment)