Java has been around since 1995, but modern Java (17+) is nothing like the Java your textbook taught you. It's faster, cleaner, and actually enjoyable to write.

This series covers every topic on dev.java/learn — one bite at a time. No fluff. Just what you need to know.

What You Need

Before writing code, you need two things:

1. JDK (Java Development Kit)

Download from adoptium.net — pick the latest LTS version (Java 21 or 24). Think of JDK as your Java toolbox — it has everything: compiler, runtime, and useful tools.

2. A text editor or IDE

For now, any text editor works. Later we'll set up VS Code or IntelliJ.

Your First Program

Create a file called Hello.java:

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

Breaking it down like a recipe:

• public class Hello — A container called "Hello" (like a box with a label)
• public static void main(String[] args) — The entry point (the "start cooking" button)
• System.out.println(...) — Print text to screen (like console.log in JavaScript)

Run It

Open terminal, navigate to the file, and type:

javac Hello.java    # Compile: turns .java into .class (like translating a recipe into action)
java Hello          # Run: actually executes the translated code

Output:

Hello, Modern Java!

That's it. You just wrote and ran a Java program.

What Actually Happened?

Hello.java  →  javac  →  Hello.class  →  java  →  Output
  (source)     (compiler)  (bytecode)     (JVM)    (result)

Analogy: You write a recipe in English (.java). The compiler translates it into a universal language (.class bytecode). The JVM (Java Virtual Machine) reads that universal language and actually cooks the dish — on Windows, Mac, or Linux.

This "compile once, run anywhere" is Java's superpower.

What's Changed in Modern Java?

If you learned Java 8 years ago, here's what's new:

Modern Java lets you write:

void main() {
    System.out.println("No class wrapper needed!");
}

This is called an implicitly declared class — Java 21+. No public class, no public static void main(String[] args). Just your code.

JShell — Java's Scratchpad

Instead of creating files for every experiment, use JShell — Java's interactive REPL:

jshell

jshell> 2 + 2
$1 ==> 4

jshell> "Hello".toUpperCase()
$2 ==> "HELLO"

jshell> /exit

Think of JShell as a calculator for Java. Type code, see results instantly. Perfect for testing ideas without creating files.

Key Takeaways

1. JDK = compiler + runtime + tools — download from Adoptium
2. Compile & Run = javac then java
3. JVM = the magic that runs Java on any OS
4. Modern Java = less boilerplate, more productivity
5. JShell = your instant feedback playground

What's Next?

In Part 2, we'll set up VS Code and IntelliJ — your development environments. The right tools make everything easier.

This series follows dev.java/learn — the official Java learning path. Each article covers one topic, explained simply.