JShell

Introduction to JShell

JShell, short for Java Shell, is a tool that allows developers to interactively experiment with Java code snippets. It was introduced as a standard component of the Java Development Kit (JDK) in Java 9. JShell serves as a Read-Eval-Print-Loop (REPL) interactive program.

Here's how JShell works:

• Read: You input Java code snippets or commands into the JShell terminal.
• Eval: JShell evaluates and executes the code you input.
• Print: The results of the code execution are immediately displayed in the terminal.
• Loop: JShell repeats the process, waiting for more input from you.

Using JShell, developers can quickly try out new ideas, test code snippets, and get instant feedback on their code's behavior. It's particularly useful for learning Java concepts, prototyping, and exploring APIs.

JShell operates in a terminal environment, accessible through the command line on Windows, macOS, and Linux. It provides a simple and safe way to experiment with Java without the need to write full programs and compile them.

However, it's important to note that JShell is not a replacement for an Integrated Development Environment (IDE). While JShell offers an interactive environment, IDEs like IntelliJ IDEA or Eclipse provide a comprehensive set of tools for efficient Java development.

Using JShell

Using JShell is quite straightforward. It provides an interactive environment where you can input Java code snippets and immediately see the results. Here's how you can use JShell:

• Launching JShell: Open your command prompt or terminal and type jshell followed by the Enter key. This will start the JShell interactive session.
• Entering Code: In the JShell prompt, start typing your Java code. You can enter single-line or multi-line code snippets. Press Enter after each line.
• Executing Code: As you enter a line of code, JShell will immediately execute and display the output if applicable. You don't need to explicitly compile or run the code.
• Using Up and Down Arrows: Use the up and down arrow keys to navigate through the history of commands you've entered. This makes it easy to make modifications and re-run code.
• Multi-Line Input: To input multi-line code, use curly braces ({ and }). After typing an opening brace, the JShell prompt will change, indicating that you're entering a multi-line block. Keep entering code lines until you close the brace.
• Viewing Command Help: Use the /help command to get a list of available JShell commands. You can also get specific help for a command by using /help commandName.
• Exiting JShell: To exit JShell, type /exit and press Enter. This will take you back to the regular command prompt or terminal.

JShell is particularly useful for trying out new code ideas, testing code snippets, and exploring Java's features in an interactive manner. It's a great tool for learning and prototyping, offering immediate feedback on your code's behavior.