Java is a general-purpose, object-oriented programming language whose programs compile to bytecode that runs on the Java Virtual Machine (JVM). Because the JVM exists for every major operating system, the same compiled program runs on Windows, macOS and Linux without changes: "write once, run anywhere". It powers banking systems, Android apps, big-data tools and most of the test automation tools QA engineers use.
A Short History of Java
- 1991: James Gosling and a small team at Sun Microsystems start a project for programming consumer devices; the language is first called Oak.
- 1995: renamed Java and released publicly, with web browsers running Java applets.
- 2006–2007: Sun releases Java as open source, the basis of today's OpenJDK.
- 2010: Oracle acquires Sun Microsystems and becomes Java's steward.
- 2018 onwards: a new version every six months, with a long-term support (LTS) release every two years: Java 17 (2021), 21 (2023) and 25 (2025).
How Java Works
You write source code in .java files. The compiler javac turns it into bytecode in .class files. The JVM loads that bytecode, verifies it, interprets it, and compiles frequently used code to native machine code with its just-in-time (JIT) compiler. The details are in How Java Code Runs.
Key Features of Java
| Feature | What it means in practice |
|---|---|
| Platform independent | Bytecode runs on any JVM, so one build works on every OS. Your Selenium suite runs the same on a Windows laptop and a Linux Jenkins agent. |
| Object-oriented | Code is organised into classes and objects with encapsulation, inheritance, polymorphism and abstraction, the basis of the Page Object Model. |
| Strongly and statically typed | Every variable has a type checked at compile time, so many mistakes are caught before the program runs. |
| Automatic memory management | The garbage collector frees objects you no longer use; there are no pointers to free by hand. |
| Robust | Exception handling, array bounds checking and type safety make failures explicit instead of silently corrupting data. |
| Secure | Bytecode verification, no direct memory access, and a mature security model and libraries for cryptography and TLS. |
| Multithreaded | Threads and concurrency utilities are built in, which is what lets TestNG run tests in parallel. |
| High performance | The JIT compiler optimises hot code at run time, so long-running Java programs are fast. |
| Huge ecosystem | Maven Central hosts libraries for almost anything: Selenium, TestNG, JUnit, REST Assured, Apache POI, Jackson. |
| Backward compatible | Code written for old versions usually runs on new JVMs, which keeps long-lived projects maintainable. |
Where Java Is Used
- Enterprise back ends: banking, insurance, e-commerce and government systems, often with Spring Boot.
- Android apps (alongside Kotlin, which also runs on the JVM).
- Big data and streaming: Hadoop, Kafka, Elasticsearch.
- Developer and test tools: Maven, Jenkins, IntelliJ IDEA, Selenium Grid, JMeter.
Why Testers Learn Java
Selenium, TestNG, REST Assured, Cucumber, Appium's Java client and JMeter are all Java tools, and Java remains the most requested language in SDET job listings in India. Learning it lets you build frameworks, read the application's code when debugging, and clear coding rounds. The Java for Testers guide lists exactly which parts to learn.
Java vs JavaScript
Despite the name, they're different languages. Java is compiled to bytecode and statically typed; JavaScript is dynamically typed and runs in browsers and Node.js. Testers meet JavaScript in Playwright, Cypress and Postman scripts, and Java in Selenium and REST Assured frameworks.
FAQs
Who created Java?
James Gosling led the team at Sun Microsystems that created Java; it was released in 1995. Oracle has owned and stewarded Java since acquiring Sun in 2010.
Why is Java called platform independent?
Because javac compiles source code into bytecode instead of machine code for one CPU, and every operating system has a JVM that runs that same bytecode.
Is Java still worth learning in 2026?
Yes. It's one of the most used languages for enterprise systems and the most requested language for Selenium and API automation roles, with new LTS releases every two years.
What are the main editions of Java?
Java SE (Standard Edition, the core language and libraries), Jakarta EE (formerly Java EE, for enterprise servers) and Java ME (for small devices). See Java SE vs Java EE vs Java ME.
