Check and Set Java JDK Versions on macOS

Understanding Java and JDK

Before diving into the commands, let’s clarify:

• Java: A programming language used to create software applications.
• JDK (Java Development Kit): A toolkit that includes the Java Runtime Environment (JRE), compiler, debugger, and other tools needed to develop Java applications.

Checking the Current JDK Version

1. Open Terminal: Use the Spotlight search (Command + Space) or navigate to Applications > Utilities > Terminal.
2. Execute the Command: Type the following command and press Enter:

   java -version
   

   This will display the installed Java version. If no output appears, it means Java is not installed.

Installing a Specific JDK

If you need to install a different JDK (e.g., for a specific project or environment), follow these steps:

1. Download the JDK: Visit the Oracle website (https://www.oracle.com/java/technologies/downloads/) and download the desired JDK for macOS.
2. Extract the Archive: Double-click the downloaded DMG file and drag the JDK folder to the /Library/Java/JavaVirtualMachines directory.
3. Update Environment Variables: Open Terminal and execute the following command to update the environment variables:

   sudo nano /etc/profile
   

   Add the following line to the end of the file, replacing /Library/Java/JavaVirtualMachines/jdk-11.0.1.jdk/Contents/Home with the actual path to your JDK:

   export JAVA_HOME="/Library/Java/JavaVirtualMachines/jdk-11.0.1.jdk/Contents/Home"
   

   Save the file (Command + X, then Y) and close the Terminal.

4. Reload Environment Variables: Open a new Terminal window or execute the following command in the existing one:

   source /etc/profile
   

Setting a Default JDK

To set a specific JDK as the default, use the following command, replacing /Library/Java/JavaVirtualMachines/jdk-11.0.1.jdk/Contents/Home with the desired JDK path:

sudo defaults write /Library/Java/JavaVirtualMachines/jdk-11.0.1.jdk/Contents/Home/bin/java -currentVersion -XstartOnFirstThread

Verifying the Default JDK

To check the current default JDK, execute the following command:

/usr/libexec/java_home -V

Additional Tips

• Homebrew: If you use Homebrew, you can install and manage JDKs using the brew command. For example, to install JDK 11:

  brew install openjdk@11
  

• Multiple JDKs: You can have multiple JDKs installed and switch between them using the JAVA_HOME environment variable or tools like jenv or sdkman.

By following these steps, you can effectively manage Java JDK versions on your macOS system.