This guide covers how to install Java 21 (or greater) on macOS, Windows, and Linux, along with setting up the JAVA_HOME environment variable.

• macOS Installation
• Windows Installation
• Linux Installation
• Setting up JAVA_HOME
• Verifying Installation

1. Update Homebrew:

   brew update

2. Install OpenJDK 21:

   brew install openjdk@21

3. Create symlink (if needed):

   sudo ln -sfn $(brew --prefix openjdk@21)/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk-21.jdk

1. Download the macOS .dmg installer from:

   • Oracle JDK
   • Adoptium (Eclipse Temurin)

2. Run the installer and follow the prompts.

1. Download the installer:

   • Visit Oracle JDK Downloads or Adoptium
   • Download the Windows .msi or .exe installer for Java 21

2. Run the installer:

   • Double-click the downloaded file
   • Follow the installation wizard
   • Note the installation path (typically C:\Program Files\Java\jdk-21)

3. Continue to Setting up JAVA_HOME on Windows

1. Download the ZIP version of JDK 21
2. Extract to a directory (e.g., C:\Java\jdk-21)
3. Continue to Setting up JAVA_HOME on Windows

# Update package lists
sudo apt update

# Install OpenJDK 21
sudo apt install openjdk-21-jdk

# Verify installation
java -version

# Install OpenJDK 21
sudo yum install java-21-openjdk-devel

# Or for newer versions:
sudo dnf install java-21-openjdk-devel

# Install OpenJDK 21
sudo pacman -S jdk21-openjdk

1. Download the tar.gz archive:

   wget https://download.oracle.com/java/21/latest/jdk-21_linux-x64_bin.tar.gz

2. Extract to /opt:

   sudo mkdir -p /opt/java
   sudo tar -xzf jdk-21_linux-x64_bin.tar.gz -C /opt/java

3. Continue to Setting up JAVA_HOME on Linux

1. Find your Java installation path:

   /usr/libexec/java_home -v 21

2. Add to your shell profile (.zshrc for Zsh or .bash_profile for Bash):

   # Open your profile
   nano ~/.zshrc
   
   # Add these lines:
   export JAVA_HOME=$(/usr/libexec/java_home -v 21)
   export PATH="$JAVA_HOME/bin: $PATH"

3. Reload your profile:

   source ~/.zshrc

1. Open Environment Variables:

   • Right-click on "This PC" or "My Computer"
   • Select "Properties"
   • Click "Advanced system settings"
   • Click "Environment Variables"

2. Create JAVA_HOME variable:

   • Under "System variables", click "New"
   • Variable name: JAVA_HOME
   • Variable value: C:\Program Files\Java\jdk-21 (adjust to your installation path)
   • Click "OK"

3. Update PATH variable:

   • Find "Path" under "System variables"
   • Click "Edit"
   • Click "New"
   • Add: %JAVA_HOME%\bin
   • Click "OK" on all dialogs

4. Restart Command Prompt or PowerShell for changes to take effect

1. Add to your shell profile (.bashrc, .bash_profile, or .zshrc):

   # Open your profile
   nano ~/. bashrc
   
   # Add these lines (adjust path if using manual installation):
   export JAVA_HOME=/usr/lib/jvm/java-21-openjdk-amd64
   export PATH=$JAVA_HOME/bin: $PATH

   For manual installation in /opt:

   export JAVA_HOME=/opt/java/jdk-21
   export PATH=$JAVA_HOME/bin:$PATH

2. Reload your profile:

   source ~/.bashrc

After installation and setting up JAVA_HOME, verify everything is working:

# Check Java version
java -version

# Check Java compiler version
javac -version

# Verify JAVA_HOME is set
echo $JAVA_HOME    # macOS/Linux
echo %JAVA_HOME%   # Windows (CMD)
echo $env:JAVA_HOME # Windows (PowerShell)

Expected output:

openjdk version "21.0.x" 2024-xx-xx
OpenJDK Runtime Environment (build 21.0.x+xx)
OpenJDK 64-Bit Server VM (build 21.0.x+xx, mixed mode, sharing)

# Install SDKMAN!
curl -s "https://get.sdkman.io" | bash

# Install Java 21
sdk install java 21-open

# Switch between versions
sdk use java 21-open

# Install jEnv
brew install jenv

# Add Java version
jenv add $(/usr/libexec/java_home -v 21)

# Set global version
jenv global 21

• Ensure JAVA_HOME/bin is in your PATH
• Restart your terminal or IDE

• Check for typos in environment variable names
• Ensure you've restarted your terminal/command prompt
• On Windows, verify you edited "System variables" not "User variables"

• Use version management tools (SDKMAN!, jEnv)
• Ensure your PATH prioritizes the correct Java installation

The JAVA_HOME environment variable is essential because:

1. Build Tools: Maven, Gradle, and Ant use JAVA_HOME to locate the JDK
2. IDEs: IntelliJ IDEA, Eclipse, and VS Code rely on it for project configuration
3. Application Servers: Tomcat, WildFly, and other servers need it to run
4. Scripts: Many shell scripts and batch files reference JAVA_HOME
5. Consistency: Provides a single source of truth for Java location across all tools

• Oracle JDK Documentation
• OpenJDK Installation Guide
• Adoptium (Eclipse Temurin)
• SDKMAN!