Upgrade to OpenJDK 21 on macOS

Upgrade to OpenJDK 21 on macOS | Generated by AI

Home 2025.08

Since you currently have OpenJDK 17 installed via Homebrew on your macOS system, here’s a concise guide to install OpenJDK 21, which is the latest Long Term Support (LTS) release as of your current date, July 1, 2025. You can install OpenJDK 21 alongside OpenJDK 17 and switch between them as needed. The simplest method is using Homebrew, but I’ll also provide a manual installation option.

Method 1: Install OpenJDK 21 Using Homebrew (Recommended)

Homebrew is already installed on your system, as indicated by your current Java version. This is the easiest and most maintainable approach.

Update Homebrew: Ensure Homebrew is up to date to fetch the latest packages:
```
brew update
```
Install OpenJDK 21: Homebrew provides a specific formula for OpenJDK 21. Run the following command:
```
brew install openjdk@21
```
This installs OpenJDK 21 in a keg-only manner, meaning it won’t be symlinked into /usr/local/bin to avoid conflicts with other Java versions.
Add OpenJDK 21 to Your Path: To use OpenJDK 21, you need to add it to your system’s PATH. Homebrew will provide instructions after installation, but typically, you can link it temporarily or permanently:
- Temporary (for the current session):
```
export PATH="/opt/homebrew/opt/openjdk@21/bin:$PATH"
```
- Permanent (add to shell configuration): Open your shell configuration file (likely ~/.zshrc since macOS uses Zsh by default):
```
nano ~/.zshrc
```
  Add the following line:
```
export PATH="/opt/homebrew/opt/openjdk@21/bin:$PATH"
```
  Save and close the file, then apply the changes:
```
source ~/.zshrc
```

Set JAVA_HOME: To ensure Java applications can locate OpenJDK 21, set the JAVA_HOME environment variable:

export JAVA_HOME=$(/usr/libexec/java_home -v 21)

Add this to your ~/.zshrc for permanence:

echo 'export JAVA_HOME=$(/usr/libexec/java_home -v 21)' >> ~/.zshrc
source ~/.zshrc

Verify Installation: Check that OpenJDK 21 is installed and active:

java -version

You should see output similar to:

openjdk 21.0.1 2023-10-17
OpenJDK Runtime Environment (build 21.0.1+12)
OpenJDK 64-Bit Server VM (build 21.0.1+12, mixed mode, sharing)

Switching Between Java Versions: Since you have OpenJDK 17 installed, you can switch between versions using /usr/libexec/java_home. For example:

To use OpenJDK 17:

export JAVA_HOME=$(/usr/libexec/java_home -v 17)

To use OpenJDK 21:

export JAVA_HOME=$(/usr/libexec/java_home -v 21)

Alternatively, consider using a version manager like jenv (install via brew install jenv) for easier switching:

jenv add /Library/Java/JavaVirtualMachines/openjdk-21.jdk/Contents/Home
jenv add /Library/Java/JavaVirtualMachines/openjdk-17.jdk/Contents/Home
jenv enable-plugin export
jenv global 21

Method 2: Manual Installation

If you prefer not to use Homebrew, you can manually install OpenJDK 21.

Download OpenJDK 21:
- Visit the official OpenJDK website (jdk.java.net/21) or a trusted provider like Oracle, Azul, or Adoptium.
- For Apple Silicon (M1/M2), download the macOS/AArch64 tar.gz file. For Intel-based Macs, choose macOS/x64.
- Example: From Oracle’s JDK 21 download page, select the ARM64 or x64 tar.gz file.
Verify the Download: Check the integrity of the downloaded file using its SHA256 checksum:
```
shasum -a 256 openjdk-21.0.1_macos-aarch64_bin.tar.gz
```
Compare the output with the checksum provided on the download page.
Extract the File: Extract the tar.gz file to a desired directory, such as your home directory:
```
tar -xf openjdk-21.0.1_macos-aarch64_bin.tar.gz -C ~/OpenJDK
```
The JDK will be extracted to ~/OpenJDK/jdk-21.0.1.jdk/Contents/Home.
Move to System Directory (Optional): For consistency, you can move the JDK to the standard macOS Java directory:
```
sudo mv ~/OpenJDK/jdk-21.0.1.jdk /Library/Java/JavaVirtualMachines/
```

Set JAVA_HOME and PATH: Update your ~/.zshrc to include:

export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk-21.0.1.jdk/Contents/Home
export PATH=$JAVA_HOME/bin:$PATH

Apply the changes:

source ~/.zshrc

Verify Installation: Confirm the installation:
```
java -version
```
Ensure it shows OpenJDK 21.

Notes

Apple Silicon Compatibility: Ensure you download the AArch64 build for M1/M2 Macs to avoid performance issues. Homebrew automatically selects the correct architecture.
Multiple JDKs: macOS supports multiple JDKs in /Library/Java/JavaVirtualMachines/. Use /usr/libexec/java_home -v <version> to switch between them.
Homebrew Advantage: Homebrew simplifies updates (brew upgrade openjdk@21) and ensures compatibility with your system.
Alternative Providers: You can also use Azul Zulu or Eclipse Temurin builds of OpenJDK 21, available from their respective websites (e.g., azul.com or adoptium.net).

If you encounter issues, let me know, and I can help troubleshoot

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