JShell in Java 9: Code Faster, Learn Easier, Build Smarter

Java has long been known for its power — and its boilerplate. But with Java 9, a long-awaited feature finally arrived to change that: JShell.

If you've ever envied the quick, interactive workflows of Python or JavaScript developers, good news — now you can do the same in Java.

What Is JShell?

JShell is Java’s official REPL (Read-Eval-Print Loop). It lets you run Java code snippets interactively, without setting up a full project, writing a main() method, or compiling anything.

It's like having a Java playground at your fingertips.

Why Use JShell?

Whether you're a junior dev or a senior building complex APIs, JShell helps you:

Test ideas instantly
Experiment with code safely
Learn Java syntax interactively
Prototype logic without the overhead

Think of it as your sandbox for Java development.

Getting Started

To launch JShell, make sure you have Java 9 or later installed. Then, open your terminal and run:

jshell

You'll drop into the interactive prompt:

|  Welcome to JShell -- Version 9.0
|  For an introduction type: /help intro
jshell>

Now, you're ready to start playing!

Basic Examples

Try simple variable declarations:

int x = 10;
x * 2

JShell immediately evaluates and returns:

$1 ==> 20

Try a method:

int square(int n) {
    return n * n;
}
square(5)

You get:

$2 ==> 25

Handy JShell Commands

JShell isn’t just about code — it’s got powerful built-in commands too:

Command	What It Does
`/list`	Shows your current session code
`/save my.jsh`	Saves your session to a file
`/reload`	Clears and reloads your session
`/help`	Lists all available commands

Auto-imports include java.util.*, java.math.*, and more — no need to manually import common packages.

Real-World Use Cases

Here’s how JShell can help in actual development:

Testing new APIs without spinning up full projects
Debugging methods on the fly
Teaching or learning Java in a hands-on way
Refining algorithms quickly during development

JShell vs Traditional Java

Feature	JShell	Traditional Java
Setup Time	Instant	Requires project setup
Syntax	Snippet-friendly	Requires full structure
Compilation	Not needed	Required
Use Case	Prototyping & learning	Production-ready apps

JShell won’t replace your IDE or build tools — but it will boost your productivity and creativity.

Pro Tip: Integrate JShell Into Your Workflow

JShell shines during early development, algorithm planning, or debugging. Keep a JShell session open while coding — it’s faster than repeatedly compiling and running your app.

Final Thoughts

JShell is one of Java 9’s most underrated features — a tool that makes Java more interactive, approachable, and fun.

It’s time to stop writing full-blown classes just to test a line of code. Jump into JShell, and start building smarter and faster today.

Personally, I use it to test new java features out, much faster than having to create a project just to test functionalities.

Try this challenge: Open JShell and write a method that checks if a number is prime. Hint: You don’t need to import anything — just code!