# JShell: Java's Built-In Scratchpad for Trying Code Fast > Source: > Published: 2026-06-21 07:08:44+00:00 Here's a familiar feeling. You want to test one small thing in Java — maybe how `String.substring()` behaves, or whether a regex pattern matches. So you create a file, write a class, add a `main` method, type `System.out.println` , compile, run. All that ceremony for a one-line answer. JShell does away with the ceremony. It's a read-eval-print loop (REPL) that ships with the JDK since Java 9. You type Java code, press Enter, and see the result immediately. No class, no `main` method, no compile step. Think of it as a calculator for Java. Open a terminal and type: ``` jshell ``` If your JDK is installed and on your PATH, you'll see a welcome message and the `jshell>` prompt. That's it. You're in. If you get a "command not found" error, double-check that the JDK (not just the JRE) is installed and the `bin` folder is on your PATH. In JShell, the bits of code you type are called **snippets**. A snippet can be an expression, a variable, a method, or even a full class. Let's try a few: ``` php jshell> int age = 25 age ==> 25 jshell> age * 2 $2 ==> 50 jshell> "hello".toUpperCase() $3 ==> "HELLO" ``` Notice two things. First, no semicolons needed. JShell adds them for you if you forget. Second, when you type an expression without storing it in a variable, JShell creates a **scratch variable** for you automatically (`$2` , `$3` , and so on). You can reuse these later: ``` php jshell> $2 + 10 $5 ==> 60 ``` This is handy when you're poking around and don't want to name every intermediate result. You can define full methods in JShell, not just expressions. Here's a simple one: ``` jshell> int square(int n) { ...> return n * n; ...> } | created method square(int) jshell> square(7) $7 ==> 49 ``` The `...>` prompt means JShell knows you're in the middle of a multi-line snippet and is waiting for you to finish. Close the braces and press Enter. Classes work the same way. You can define a class, instantiate it, and call methods on it, all without leaving the prompt. This is where JShell gets genuinely useful. If you redefine a method or variable, the old version is replaced. No need to start over. ``` jshell> String grade(int score) { ...> if (score >= 90) return "Pass"; ...> return "Fail"; ...> } | created method grade(int) jshell> grade(85) $3 ==> "Fail" ``` That pass threshold feels too strict. Just retype the method with a change: ``` jshell> String grade(int score) { ...> if (score >= 80) return "Pass"; ...> return "Fail"; ...> } | modified method grade(int) jshell> grade(85) $5 ==> "Pass" ``` The method updated in place. Any other methods that called `grade` will use the new version automatically. For longer snippets, use the `/edit` command to pop open a text editor instead of retyping: ``` jshell> /edit grade ``` Make your changes, save, and close the editor. JShell picks up the new version. JShell has about 20 commands, all starting with a forward slash. You won't need all of them. Here are the ones that matter day to day: ``` /list # show everything you've typed, with IDs /vars # show all variables and their values /methods # show all methods you've defined /types # show classes, interfaces, and enums /imports # show active imports ``` To manage your session: ``` /save myfile.jsh # save all snippets to a file /open myfile.jsh # load snippets back in later /reset # wipe everything and start fresh /drop 3 # remove a specific snippet by ID /history # see everything typed, in order /exit # leave JShell ``` Pro tip: command abbreviations work as long as they're unique. `/l` runs `/list` . `/v` runs `/vars` . `/sa` runs `/save` (since `/s` alone is ambiguous between `/save` and `/set` ). Press Tab while typing and JShell fills in the rest. This works for commands, class names, and method names. If there's more than one option, Tab shows you all of them. A few shortcuts worth knowing: `/!` `/-3` The `Shift+Tab` then `V` shortcut is a neat trick: type an expression, hit that combo, and JShell converts it into a variable declaration with the correct type filled in. By default, JShell shows a reasonable amount of feedback. But when you're learning, more detail helps. Switch to verbose mode: ``` jshell> /set feedback verbose ``` Verbose mode explains what happened after each snippet — what was created, modified, or dropped, and what type it is. Once you're comfortable, switch back to normal or concise: ``` jshell> /set feedback normal jshell> /set feedback concise ``` There's also `silent` mode if you want zero output (useful when piping JShell into scripts). One complaint people have about REPLs: you lose everything when you close them. JShell solves this with `/save` and `/open` . Before you exit, save your work: ``` /save practice.jsh ``` Next time you start JShell, load it back: ``` /open practice.jsh ``` You can also pass a file directly when launching: ``` jshell practice.jsh ``` This makes JShell practical for more than throwaway experiments. Keep a `.jsh` file of helper methods you use often, and load it whenever you start a session. JShell isn't a replacement for your IDE. It's a tool for specific moments: `LocalDate.of(2026, 2, 31)` does? Find out in two seconds instead of writing a test class.The thing I like most about JShell is that it removes the fear of experimentation. In a normal Java project, trying something feels expensive. In JShell, it costs nothing. You type, you see, you move on. `jshell` to start it.`main` method required.`$1` , `$2` , ...) hold results you didn't name.`/list` , `/vars` , `/methods` , `/save` , `/open` , `/reset` , and `/exit` cover most of what you need.`/!` reruns your last snippet.`/set feedback verbose` while learning, then dial it back.`/save` and reload them with `/open` .Based on dev.java/learn — [JShell: The Java Shell Tool](https://dev.java/learn/jshell-tool/)