What is Java? History, Features & Editions (JDK / JRE / JVM

Java is one of the most popular and powerful programming languages in the world. It is known for its simplicity, reliability, and platform independence, making it ideal for beginners as well as professionals.

What is Java?

Java is a high-level, object-oriented, and platform-independent programming language developed by Sun Microsystems (now owned by Oracle).

It is used to build:

• Desktop applications
• Web applications
• Mobile apps (Android)
• Cloud and enterprise solutions
• Games and IoT devices

The main idea behind Java is “Write Once, Run Anywhere” (WORA) — meaning a Java program can run on any system that has a Java Virtual Machine (JVM), without needing changes.

History of Java

• 1991: Java project started by James Gosling and team at Sun Microsystems, originally named Oak.
• 1995: Officially released as Java, with the slogan “Write Once, Run Anywhere”, focusing on platform independence.
• 1998: Launch of Java 2 (J2SE, J2EE, J2ME) – dividing Java into Standard, Enterprise, and Micro Editions.
• 2004: Java 5 introduced major features like Generics, Enhanced for-loop, and Annotations.
• 2006: Sun Microsystems made Java open-source under the GPL license.
• 2009: Oracle Corporation acquired Sun Microsystems and took over Java’s development.
• 2011–2017: Regular improvements – Java 7, 8 (Lambda Expressions, Stream API), and 9 (Modular System).
• 2018–Present: Rapid 6-month release cycle – Java 11, 17, 21 adding better performance, security, and modern features.
• Today: Java remains one of the most powerful, secure, and versatile programming languages used in web, mobile, enterprise, and cloud applications.

Key Features of Java

Here are the major features that make Java so popular:

1. Simple & Easy to Learn

Java has a clean, easy-to-read syntax similar to English. It eliminates complex features like pointers and operator overloading.

2. Object-Oriented

Everything in Java revolves around objects — making code modular, reusable, and easier to maintain.

3. Platform-Independent

Java code is compiled into bytecode, which runs on any system with a JVM. That’s what gives Java its “Write Once, Run Anywhere” power.

4. Secure

Java provides built-in security through its JVM, classloader, and security manager, preventing unauthorized access.

5. Robust

It has strong memory management, exception handling, and type checking, which reduce runtime errors.

6. Multithreaded

Java allows multiple threads (tasks) to run simultaneously, improving performance and responsiveness.

7. High Performance

With the Just-In-Time (JIT) compiler, Java executes faster than traditional interpreted languages.

8. Distributed & Networked

Java supports distributed applications using technologies like RMI, JSP, and Servlets.

9. Dynamic & Extensible

Classes can be loaded dynamically at runtime, and Java easily integrates with other technologies like Kotlin, Scala, and Groovy.

Editions of Java (JDK / JRE / JVM)

Java is divided into three main editions and three core components.

Java Components

1. JDK (Java Development Kit)

• The complete toolkit for developers.
• Includes JRE + development tools (compiler, debugger, etc.).
• Used to write, compile, and run Java programs.

2. JRE (Java Runtime Environment)

• Provides the libraries and JVM needed to run Java applications.
• It cannot compile Java programs — only executes them.

3. JVM (Java Virtual Machine)

• The heart of Java technology.
• Converts bytecode into machine code.
• Handles memory management, garbage collection, and security.

Short Version:

JDK = JRE + Development Tools

JRE = JVM + Libraries

How Java Works (Simplified)

1. You write code in .java file.
2. The Java compiler (javac) converts it into bytecode (.class file).
3. The JVM interprets and executes this bytecode on any system.

Java Source Code (.java)
        ↓
   Java Compiler
        ↓
   Bytecode (.class)
        ↓
   JVM (Execution)

Real-World Use Cases of Java

• Android Development (Apps and Games)
• Web Applications (Spring, Hibernate)
• Big Data Technologies (Hadoop, Spark)
• Banking & FinTech Systems
• Enterprise Software (ERP, CRM, Billing Systems)

Summary Table

🏆 Top 5 Java Interview Questions - Java Overview, Concepts, Core, JDK/JVM, Essentials

1. What is Java?

Answer: Java is a high-level, object-oriented, and platform-independent programming language developed by Sun Microsystems (now Oracle).

It is used for desktop, web, mobile, and enterprise applications, following the principle of “Write Once, Run Anywhere.”

2. What is the difference between JDK, JRE, and JVM?

Answer:

Formula:

JDK = JRE + Development Tools

JRE = JVM + Libraries

3. What is the meaning of “Write Once, Run Anywhere”?

Answer: It means Java programs, once compiled into bytecode, can run on any platform that has a JVM, without recompiling — ensuring platform independence.

4. What are the main features of Java?

Answer:

• Simple and Object-Oriented
• Platform-Independent
• Secure and Robust
• Multithreaded and High Performance (JIT compiler)
• Distributed and Dynamic

5. Explain the working of Java (Execution Process).

Answer:

1. Source Code written → MyProgram.java
2. Compiled by javac → produces bytecode (MyProgram.class)
3. JVM interprets the bytecode and executes it on any OS

Java Source Code (.java)
        ↓
   Java Compiler (javac)
        ↓
   Bytecode (.class)
        ↓
   JVM (Execution)