update-java-alternatives

update-java-alternatives [options]

--list
    Lists available Java alternatives.

--set
    Sets the default Java alternative to the specified ID. The ID is typically the name of the Java directory.

--jre-priority
    Specifies the JRE priority for the automatic mode.

--plugin
    Configures the Java browser plugin.

--all
    Sets up all Java alternatives.

--verbose
    Displays verbose output.

--help
    Displays help message.

--version
    Displays the version of the command.

The `update-java-alternatives` command is a Debian-specific utility designed to manage Java alternatives on a system. It allows administrators to easily switch between different Java Development Kits (JDKs) or Java Runtime Environments (JREs) installed on the machine. This is crucial for environments where multiple Java versions are required for different applications or development purposes. The command automatically updates symbolic links to ensure that the correct Java version is used by the system and applications. It handles tasks like setting the default Java version, configuring browser plugins, and managing alternatives for Java-related tools such as `javac`, `java`, `javadoc`, `jar`, and more. This ensures a consistent and predictable Java environment.

It's typically used in Debian-based systems like Ubuntu, Linux Mint, and Debian itself. It simplifies the process of changing the system's active Java version without manually editing configuration files or manipulating symbolic links. The configuration is often managed through the Debian alternatives system, ensuring proper integration with package management.

This command is specific to Debian-based systems and will not work on other Linux distributions like Red Hat or SUSE. It relies on the Debian alternatives system. Also, the tool assumes the existence of alternatives entries for javac, jar and others, which should be provided by the java package itself.

Listing Available Java Alternatives:
`update-java-alternatives --list`

Setting a Specific Java Version:
`update-java-alternatives --set java-1.8.0-openjdk-amd64`

Configuring the Java Browser Plugin:
`update-java-alternatives --plugin`

The `update-java-alternatives` command primarily manipulates symbolic links in directories such as `/usr/bin` and `/etc/alternatives`. These links point to the actual Java executables and libraries. The command also updates configuration files to reflect the selected Java version. It uses the alternatives system to properly register each java binary to its alternatives path.

The `update-java-alternatives` command was developed as part of the Debian project to simplify the management of multiple Java installations. Its purpose was to address the common problem of applications requiring specific Java versions. Before its introduction, system administrators often had to manually manage symbolic links and environment variables to switch between Java versions, a process that was both time-consuming and error-prone. The command automates this process, integrating seamlessly with the Debian package management system. It has been continuously maintained and improved over the years, becoming a standard tool for managing Java environments on Debian-based distributions.

alternatives(8)