Programming language · Since 1995

Java

Java is a statically typed, object-oriented language that runs on the JVM and powers enterprise backends, Android apps, and large-scale data systems.

Start the guide Discussions

Java is a general-purpose, object-oriented programming language first released by Sun Microsystems in 1995 and now developed by Oracle together with the OpenJDK community. Java source code is compiled into bytecode that runs on the Java Virtual Machine (JVM), so the same program runs on Windows, macOS, and Linux without being recompiled. Automatic memory management and a strict static type system catch many errors early and keep large codebases maintainable.

Java is especially strong in server-side software that has to run reliably for years: web services and APIs built with frameworks such as Spring, financial and transaction-processing systems, and data platforms like Apache Kafka, Hadoop, and Spark. It also has a long history in Android development. The JVM's just-in-time compiler and mature garbage collectors deliver solid performance for long-running workloads, and Maven Central hosts a vast collection of open-source libraries.

To get started, install a JDK, for example an OpenJDK build such as Eclipse Temurin, then run a single source file directly with the java command or experiment interactively in JShell. The Learn section on dev.java walks through the language step by step, and the Java SE API documentation is the reference you will return to most often. Once a project grows beyond a few files, add a build tool such as Maven or Gradle and an IDE. In production, teams usually standardize on a long-term support (LTS) release.

Highlights

Write once, run anywhere

Programs compile to platform-independent bytecode that runs on any JVM, so the same build works across operating systems and CPU architectures.

Garbage collection and JIT compilation

The garbage collector reclaims objects that are no longer used, ruling out a whole class of memory-freeing bugs, while the JIT compiler optimizes frequently executed code at run time.

Static typing that keeps evolving

Classes, interfaces, and generics catch type errors at compile time, and newer features such as lambdas, records, and pattern matching make code more concise.

Rich standard library and ecosystem

The standard library covers collections, concurrency, I/O, networking, and much more, and Maven Central adds a wide range of open-source libraries.

Where it is used

Enterprise backends and web APIs
Android apps
Big data and streaming platforms
Financial and high-volume transaction systems

Install

1
Install a JDK
Download and install an OpenJDK build such as Eclipse Temurin from adoptium.net. You can also use a package manager: winget on Windows, Homebrew on macOS, or your distribution's package manager or SDKMAN! on Linux. Unless you have a specific need, choose an LTS release.
2
Verify the installation
Open a new terminal and check that both the runtime (java) and the compiler (javac) print their versions. If the command is not found, add the JDK's bin directory to PATH and set JAVA_HOME to the JDK folder.
```
java -version && javac -version
```
3
Run your first program
Save the example below as Hello.java and run it directly with the java command; the JDK compiles and runs the source file in a single step.
```
java Hello.java
```

Your first program

Your first Java program

The Hello class defines a main method, the entry point the JVM calls when the program starts, and System.out.println prints a line to the console. The file name must match the name of the public class. Recent JDKs can run a single source file directly with java Hello.java, compiling it in memory without a separate javac step; larger projects are compiled with javac or a build tool before the classes are run.

Hello.java

public class Hello {
    public static void main(String[] args) {
        System.out.println("Hello, world!");
    }
}

java Hello.java

Everyday tools

javac: The Java compiler included in the JDK; it turns .java source files into .class files containing bytecode.
JShell: An interactive REPL included in the JDK for trying out expressions, statements, and APIs without writing a class.
Maven: A build tool that manages dependencies and the build lifecycle declaratively through a pom.xml file.
Gradle: A flexible build tool configured with Kotlin or Groovy scripts; it is also the standard build system for Android.

Step-by-step guide

Six chapters that take you from installation to the core ideas of Java.

Official docs and resources

Discussions

Start a discussion

Ask questions, share experience and trade opinions about Java.

No discussions yet. Start the first one.