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Appendix A: Installing Java JDK

To use jshell and run the examples in this book, you need Java JDK version 9 or later installed on your computer. This appendix will help you check if you already have Java installed and guide you through installation if needed.

Checking Your Current Java Installation

First, let’s see if you already have Java installed and what version it is.

Step 1: Open Your Terminal or Command Prompt

On Windows:

  • Press Windows + R, type cmd, and press Enter

  • Or search for "Command Prompt" in the Start menu

On macOS:

  • Press Cmd + Space, type terminal, and press Enter

  • Or go to Applications > Utilities > Terminal

On Linux:

  • Press Ctrl + Alt + T

  • Or search for "Terminal" in your applications

Step 2: Check Java Version

Type the following command and press Enter:

java -version

You might see output like this:

java version "17.0.2" 2022-01-18 LTS
Java(TM) SE Runtime Environment (build 17.0.2+8-LTS-86)
Java HotSpot(TM) 64-Bit Server VM (build 17.0.2+8-LTS-86, mixed mode, sharing)

If you see a version number 9 or higher (like 11, 17, 21), you’re all set!

If you see an error like "java is not recognized" or "command not found", you need to install Java.

If you see a version number lower than 9 (like 1.8), you should update to a newer version.

Step 3: Check if You Have the JDK (Not Just JRE)

To use jshell, you specifically need the JDK (Java Development Kit), not just the JRE (Java Runtime Environment). Check by typing:

javac -version

You should see something like:

javac 17.0.2

If you get "javac is not recognized" or "command not found", you have the JRE but need the full JDK.

Installing Java JDK

If you need to install or update Java, here are the recommended approaches:

Option 1: Oracle JDK (Recommended for Beginners)

  1. Go to https://www.oracle.com/java/technologies/downloads/

  2. Download the latest LTS (Long Term Support) version for your operating system

  3. Run the installer and follow the setup wizard

  4. Restart your terminal/command prompt

  5. Test the installation using the commands from Step 2 above

Option 2: OpenJDK (Free Alternative)

OpenJDK is a free, open-source implementation of Java:

For Windows:

  1. Go to https://adoptium.net/

  2. Download the latest LTS version

  3. Run the installer

  4. Make sure "Set JAVA_HOME variable" is checked during installation

For macOS with Homebrew:

brew install openjdk

For Ubuntu/Debian Linux:

sudo apt update
sudo apt install openjdk-17-jdk

For Red Hat/CentOS/Fedora Linux:

sudo yum install java-17-openjdk-devel

Option 3: SDKMAN (For Advanced Users)

SDKMAN is a tool for managing multiple Java versions:

  1. Install SDKMAN: https://sdkman.io/install

  2. Install Java:

sdk install java 17.0.2-tem

Verifying Your Installation

After installation, open a new terminal/command prompt and run:

java -version
javac -version
jshell

The first two commands should show version 9 or higher. The third command should start jshell with a welcome message like:

|  Welcome to JShell -- Version 17.0.2
|  For an introduction type: /help intro

jshell>

Type /exit to quit jshell.

Troubleshooting Common Issues

"java is not recognized as an internal or external command"

On Windows:

  1. The Java installer should have set the PATH automatically

  2. If not, you may need to add Java to your PATH manually:

    • Find where Java is installed (usually C:\Program Files\Java\jdk-XX\bin)

    • Add this to your system PATH environment variable

    • Restart your command prompt

On macOS/Linux:

  1. Java might be installed but not in your PATH

  2. Try: which java to see if it’s found

  3. You may need to add Java to your PATH in your shell configuration file

Multiple Java Versions

If you have multiple Java versions installed:

On Windows: The last installed version usually becomes the default

On macOS: Use java_home to manage versions:

/usr/libexec/java_home -V

On Linux: Use update-alternatives:

sudo update-alternatives --config java

Permission Issues on macOS

If you get security warnings on macOS:

  1. Go to System Preferences > Security & Privacy

  2. Click "Allow" for Oracle or the Java installer

  3. Try the installation again

Recommended Java Versions

For this book, we recommend:

  • Java 21 LTS - Latest long-term support version (recommended)

  • Java 17 LTS - Widely used long-term support version

  • Java 11 LTS - Older but still supported LTS version

Avoid:

  • Java 8 and earlier (no jshell support)

  • Non-LTS versions unless you have a specific need

Setting Up Your Development Environment

Once Java is installed, you have several options for writing and running Java code:

Using jshell (Recommended for This Book)

jshell is perfect for learning and experimenting:

  • No need to create full programs

  • Immediate feedback on code snippets

  • Great for testing small pieces of code

  • Comes built-in with Java 9+

Start jshell by typing jshell in your terminal.

Code Editors and IDEs

For larger projects, consider these tools:

Beginner-Friendly:

  • Visual Studio Code with Java extensions - Free, lightweight

  • IntelliJ IDEA Community Edition - Free, powerful

  • Eclipse - Free, widely used

Professional:

  • IntelliJ IDEA Ultimate - Commercial, full-featured

  • NetBeans - Free, Oracle-supported

Simple Text Editors:

  • Notepad++ (Windows) - Basic syntax highlighting

  • TextEdit (macOS) - Simple text editing

  • Gedit (Linux) - Basic code editing

For this book, jshell is sufficient, but having a good editor helps when you want to save your programs.

Getting Help

If you’re still having trouble:

  1. Check your Java vendor’s documentation:

  2. University/School IT Support: Many institutions provide Java installation help

  3. Online Communities:

  4. Verify Installation:

    • Make sure you downloaded the JDK, not just the JRE

    • Ensure you downloaded the correct version for your operating system (32-bit vs 64-bit)

    • Try restarting your computer after installation

Once you have Java JDK 9 or later installed and working, you’re ready to start using jshell and following along with all the examples in this book!
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