How can I manage multiple Java versions on Mac OS X, especially when I have a newer version installed and want to install an older version?

Managing Multiple Java Versions on Mac OS X

Context:

You have successfully installed JDK 8 on your Mac OS X system. However, you now require a JDK 7 installation for development purposes. Attempting to install the older version via a DMG file generates a warning about a newer Java version being already installed, resulting in the installer's termination.

Solution:

The optimal approach to managing multiple Java versions on Mac OS X is through Homebrew, a package management system. Homebrew employs two utilities for this task:

• homebrew-cask: Installs various Java versions.
• jenv: Manages the installed Java versions.

Steps:

1. Install Homebrew.
2. Install Homebrew jenv.
3. Install Homebrew-cask.
4. Install a specific Java version using cask. (Refer to the "homebrew-cask versions" section below for details.)
5. Add the installed version to jenv for management.
6. Verify that jenv manages the version correctly.
7. Repeat steps 4-6 for each Java version required.

homebrew-cask versions:

Add the homebrew/cask-versions tap to Homebrew:

brew tap homebrew/cask-versions

Search for available versions:

brew search temurin

Install desired versions:

brew install --cask temurin8
brew install --cask temurin9

Add the installed versions to jenv:

jenv add <javaVersionPathHere>

Additional Considerations:

• Verify Java version paths using /usr/libexec/java_home -V.

• macOS differentiates Java installations based on their source:

  • Built-in JRE: /Library/Internet Plug-Ins/JavaAppletPlugin.plugin/Contents/Home
  • Apple-downloaded JDKs: /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home/
  • Oracle-downloaded JDKs: /Library/Java/JavaVirtualMachines/jdk1.8.0_11.jdk/Contents/Home

Resources:

• [Removing Java 8 JDK from Mac](https://stackoverflow.com/questions/15196242/removing-java-8-jdk-from-mac)
• [Managing Multiple Java Installations with Homebrew](http://hanxue-it.blogspot.ch/2014/05/installing-java-8-managing-multiple.html)
• [Mac Setup](http://sourabhbajaj.com/mac-setup/index.html)
• [Homebrew](http://brew.sh)
• [Homebrew Documentation](https://github.com/Homebrew/homebrew/tree/master/share/doc/homebrew#readme)
• [Homebrew Cask](https://github.com/caskroom/homebrew-cask)
• [Jenv](http://www.jenv.be)

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