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Installation path

All Java versions managed by JavaOptionsCli are installed in a centralized location: 
/opt/java
This directory is created automatically during the first installation if it doesn’t exist. The CLI checks for this directory and creates it with 0777 permissions when needed.

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Binary paths structure

Each Java version is stored in its own subdirectory within /opt/java, with binaries located in the bin folder: 
/opt/java/jdk-21/bin/java
/opt/java/jdk-21/bin/javac
/opt/java/jdk-21/bin/jar
The typical structure looks like: 
/opt/java/
├── jdk-17/
│   └── bin/
│       ├── java
│       ├── javac
│       └── jar
└── jdk-21/
    └── bin/
        ├── java
        ├── javac
        └── jar

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Update-alternatives priority system

JavaOptionsCli uses Debian’s update-alternatives system to manage multiple Java installations. When you install a new Java version, you need to provide a priority number.

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Priority format

The priority is a numeric value that determines which version gets selected automatically. Higher numbers have higher priority. Recommended format: Use the Java version number followed by two zeros. 
Java 21 → 2100
Java 17 → 1700
Java 11 → 1100

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How it works

The CLI registers three binaries for each Java installation: 
sudo update-alternatives --install /usr/bin/java java /opt/java/jdk-21/bin/java 2100
sudo update-alternatives --install /usr/bin/javac javac /opt/java/jdk-21/bin/javac 2100
sudo update-alternatives --install /usr/bin/jar jar /opt/java/jdk-21/bin/jar 2100
Each command registers:
  • The system-wide binary path (/usr/bin/java)
  • The alternative name (java)
  • The actual binary location (/opt/java/jdk-21/bin/java)
  • The priority value (2100)

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Managing alternatives

You can interact with the alternatives system through the CLI:
  • Change version: Uses update-alternatives --config to let you manually select which version to use
  • Auto mode: Uses update-alternatives --auto to automatically select the highest priority version
  • List versions: Uses update-alternatives --list to display all registered versions

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Running from tar.gz directory

The CLI must be executed from the same directory where your .tar.gz file is located.
This is a current requirement because:
  1. The CLI extracts the tar.gz file in the current working directory
  2. It looks for extracted jdk-* directories using filepath.Glob("jdk-*")
  3. It then moves the extracted directory to /opt/java

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Workflow example

# Place your tar.gz file in a directory
cd ~/downloads
ls
# jdk-21_linux-x64_bin.tar.gz

# Run JavaOptionsCli from this directory
JavaOptionsCli

# When prompted, enter the tar.gz filename
Enter the name of the tar file
jdk-21_linux-x64_bin.tar.gz
The extraction process:
  1. Extracts the tar.gz in the current directory
  2. Identifies the extracted folder (e.g., jdk-21.0.1)
  3. Moves it to /opt/java/jdk-21.0.1
  4. Registers the binaries with update-alternatives

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Making the CLI globally available

While the CLI must run from the tar.gz directory during installation, you can make the binary itself globally accessible: Option 1: Move to PATH 
sudo mv JavaOptionsCli /usr/bin/JavaOptionsCli
Option 2: Create an alias 
# Add to ~/.bashrc or ~/.zshrc
alias javaoptionscli="/path/to/JavaOptionsCli"

# Reload shell
source ~/.bashrc
This allows you to run JavaOptionsCli from any directory, but you still need to navigate to the directory containing your tar.gz files before installing a new version.

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