How to save, edit, and drop a snippet in JShell in Java 9?

Java Shell or JShell is an official REPL(Read-Evaluate-Print-Loop) introduced with Java 9. It provides an interactive shell for quickly prototyping, debugging and without the need for the main() method or the need to compile the code before executing it. JShell is easily started by typing "jshell" in the command prompt.

What are Snippets?

JShell allows the execution of Java statements, variables, methods, class definitions, imports, and expressions. These pieces of Java code are referred to as snippets. Every snippet is assigned an ID(unique) that we can use later to reference it.

Example

Below is an example to represent a snippet to add two integers:

jshell> int sum(int a, int b) 
   { return a + b; }
|  created method sum(int,int)

Save a snippet

We can save a snippet source to a file by using the "/save [-all|-history|-start] " command.

Save Modes

The following are some common JShell save modes:

• /save-all: Saves all snippets, including those that failed.
  
• /save-history: Saves just the history of commands.
  
• /save-start: Saves the startup snippets.

Syntax

The following is the syntax for saving a snippet:

/save <filename-location>

Example

Below is an example for saving a snippet:

C:\Users\User>jshell
| Welcome to JShell -- Version 9.0.4
| For an introduction type: /help intro

jshell> /save C:\Users\User\jshell.txt

The above code creates a new "jshell.txt under the specified path.

Edit a snippet

We can also edit the code in an external editor by using the "/edit" command.

Syntax

The following is the syntax for editing a snippet:

/edit <snippet-name-or-id>

Example

Below is an example for editing a snippet:

C:\Users\User>jshell
| Welcome to JShell -- Version 9.0.4
| For an introduction type: /help intro

jshell> /edit
| created method empName(String,String)

Output

This launches the JShell edit pad, where we can edit the code snippet and save it.

Jshell Edit Pad

Drop a snippet

Similarly, we can also drop a particular snippet by using the command "/drop".

Syntax

The following is the syntax to drop a snippet:

/drop <id>

Dropping All Snippets

Dropping all snippets means it clears all snippets in the current session and resets the JShell state.

Syntax

The following is the syntax for dropping all snippets a snippet:

/reset

Example

Below is an example to drop a snippet:

jshell> /drop 1
| dropped method empName(String,String)

The above command tells the JShell to drop the snippet with ID 1 from your current session. To check if the ID is dropped, run the "/list" command on the JShell, it will show all the active snippets.