update-alternatives: warning: /etc/alternatives/java is dangling

Assuming you installed the OpenJDK6 with:

sudo apt-get install openjdk-6-jdk

In Ubuntu 64 bit, make sure the paths are valid for your installation (change if using 32bit version):

/usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java/usr/lib/jvm/java-6-openjdk-amd64/bin/javac

Setup update-alternatives:

sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java" 1sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/java-6-openjdk-amd64/bin/javac" 1sudo update-alternatives --set java /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/javasudo update-alternatives --set javac /usr/lib/jvm/java-6-openjdk-amd64/bin/javac

Alternatively, make sure the correct version is checked for both Java and compiler:

sudo update-alternatives --config javasudo update-alternatives --config javac

List the installed Java alternatives with:

sudo update-alternatives --list javasudo update-alternatives --list javac

update java alternatives:

sudo update-alternatives --config javasudo update-alternatives --config javac

If you install openjdk 8 in docker. Maybe you need to install "software-properties-common"

apt-get update && apt-get install apt-file -y && apt-file update && apt-get install software-properties-common

And then you install openjdk 8 and setup update-alternatives with end number = 3

sudo apt-get install openjdk-8-jdkexport JAVA_HOME="/usr/lib/jvm/java-8-openjdk-amd64"update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java" 3update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/java-8-openjdk-amd64/bin/javac" 3