Introduction to Java

Java was created at Sun Microsystems by James Gosling’s team and released publicly in 1995. Its core promise—compile once to portable bytecode, then run on a compatible virtual machine—made it important for servers, Android’s Java-language ecosystem, enterprise systems, and developer tools. OpenJDK is the open-source reference implementation; Java evolves through regular feature and long-term-support releases.

From source to execution

The JDK supplies javac, java, documentation, debugging, packaging, and runtime tools. javac compiles source to .class bytecode. The JVM verifies, loads, interprets, and JIT-compiles hot code. The JRE describes the JVM plus runtime libraries, though modern distributions commonly ship modular runtimes rather than a separate JRE download.

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

Compile with javac Hello.java and run with java Hello. Java provides garbage collection, strong runtime checks, exceptions, reflection, concurrency, and a broad standard library. Portability still requires care around files, encodings, native integrations, versions, and deployment configuration.