Updating alternatives for JRE/JDK installations
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Packages providing a runtime or a development environment for the Java
language all use symlinks in the /etc/alternatives directory to enable
the system administrator to choose which programs to use for java,
javac, javah, etc.

The update-java-alternatives script can be used to set all the JRE/JDK
alternatives:

First, you have to decide which Java implementation to default to.

  update-java-alternatives --list

tells about the available runtime and/or development environments. The
first column shows the names to be used in for the following examples.

- Set all runtime tools to point to the <jname> alternatives:

  update-java-alternatives --jre --set <jname>

- Set all runtime tools (headless only) to point to the <jname>
  alternatives:

  update-java-alternatives --jre-headless --set <jname>

- Set all runtime and development tools to point to the <jname>
  alternatives:

  update-java-alternatives --set <jname>

- Set all runtime and development tools to auto mode:

  update-java-alternatives --auto