JShell: Java’s First Interactive Playground

Have you ever wanted to test a small snippet of Java code but didn’t feel like creating a test project or rebuilding a running one, waiting, and hoping it all works? Yes, we've all been there. Meet JShell — Java’s first interactive REPL (Read-Eval-Print Loop) introduced in Java 9.

Think of it as your new favorite sandbox — a place where you can simply write code, run it, and instantly see the results. It may not be as futuristic as AI, but for any Java developer, JShell is a real breakthrough. Trust me, once you start using it, you’ll wonder how you ever got by without it.

1. Instant Feedback: Learn and Experiment in Real-Time

JShell is like a chat window with your code. You type something in, and it immediately responds. No need to create classes, methods, or tons of template test data — you just write a command, and JShell answers. It’s perfect for testing complex logic fragments, exploring new APIs, or simply trying to understand why that line of code you wrote seems to have a mind of its own. You get instant feedback, so you can spend less time waiting and more time coding.

Example:

No more setup, no more hassle. Just write, run, and get your answer. It’s like having a direct support line with your code without all the formalities.

2. Simplified Learning and Prototyping: From Beginner to Pro

If you’re new to Java, welcome! JShell will become your best friend. It’s the perfect place to learn the basics without having to build an entire program just to understand how a loop works. You can focus on what matters instead of configuring and launching a test environment.

And if you’re an experienced developer, JShell will be your go-to tool for rapid prototyping. Got a new idea? Curious about a method from a library? Just type it in and see what happens. Skip the setup and get straight to the point.

Using JShell is like cruising in the fast lane while everyone else is stuck in traffic!

3. Scripting and Automation: Boost Your Workflow

JShell isn’t just for quick code tests. It offers a wide range of capabilities. You can save your code snippets as scripts and run them directly from the command line. This means you can automate tasks, create quick demos, or even test new libraries without needing to set up an entire project.

A real-world example: Imagine you’re trying out a new library but aren’t ready to set up a full project to see how it works. You write a script in JShell, run it, and voila — you get your answer. Efficient, effective, and no time wasted.

1. Create a .jsh file with your script:

2. Download the Apache Commons Lang library JAR file and save it in a folder. Let’s say the file is in the same folder where your .jsh script and the path is just 'commons-lang3-3.12.0.jar'.

3. Run the Script and get the output right away:

4. Autocompletion and Code Suggestions: Almost Like Copilot, but for JShell

JShell also has auto-completion features, built-in syntax checking, and smart suggestions—it was almost like a Copilot of its time. Nowadays, JShell’s autocompletion and code suggestions are no longer as interesting, so we won’t dwell on them here.

5. Integrated with JDK Tools: More Than Just a Learning Tool

JShell is more than just a sandbox; it can be a fully functional work tool. Integration with other JDK tools allows you to use it within your testing pipeline, for scripting or documentation generation.

If you're not using AI for these types of tasks due to cost, you might consider JShell as an alternative.

Final Thoughts

JShell brings interactivity to Java, helping you learn, experiment, and test code faster than ever. Whether you're a beginner trying to grasp the basics of Java or a professional looking to quickly prototype without the hassle of setting up a test environment, JShell is the tool you may not have realized you needed, but it can be incredibly helpful.

So, have you tried JShell yet? If not, now is the perfect time to give it a go. For a more in-depth look, check out the official JEP 222 documentation.

To learn more about Java 9 features, check out the article Java 9 Features: What's In It for Developers?

Key Takeaways:

- Instant Feedback: Test code snippets in real-time without setting up projects.

- Simplified Learning: Great for beginners to grasp concepts; helpful for pros to prototype quickly.

- Scripting and Automation: Save scripts, automate tasks, and test libraries easily.

- Code Completion: Auto-completion and syntax checks make coding faster and less error-prone.

- Versatile Integration: Can be used alongside other JDK tools throughout the development process.