Introduction to Java

Java is the workhorse of enterprise software — write once, run anywhere on the Java Virtual Machine.

¶What is Java?

Java is a statically-typed, object-oriented language that compiles to bytecode and runs on the JVM.

That portable runtime, a vast standard library, and decades of tooling make it a default for large, long-lived systems.

¶Your first example

Here is Java saying hello. Read it top to bottom — every line earns its place.

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

Hello, world!

¶Why learn Java?

• It powers a huge share of backend systems, Android, and big-data tooling.
• Strong typing and mature tooling keep large teams productive.
• JVM skills transfer across Kotlin, Scala, and more.

¶Where it is used

• Enterprise backends
• Android apps
• Big data (Spark, Hadoop)
• Cross-platform services

¶How this track works

Every topic here has four views, switchable with the tabs at the top of each page:

• Learn — the clear, practical walkthrough you are reading now.
• Deep — every detail: edge cases, the full API, and what is really happening.
• Reference — a scannable, no-fluff lookup for when you already know the shape.
• Cheatsheet — the one-page summary, printable, for quick recall.