How to uninstall OpenJDK?

Great question, I was wondering this myself.

I found that you can use the following to remove the openjdk-7-jre on Ubuntu 13.04:

sudo apt-get autoremove openjdk-7-jre

Press 'y' and then press enter when prompted to confirm this change. This should also clean up all the additional dependency libraries that were installed with it.

I also found you can use the following command to perform additional clean up:

sudo apt-get purge openjdk*

If you use the following command:

java -version

You should no longer see the openjdk-7-jre installed!

Hope this helps. :)

You can use the following command:

sudo apt-get purge openjdk-8-jre openjdk-8-jre-headless openjdk-7-jre gcj-4.7-base gcj-4.7-jre openjdk-6-jre-headless

In this way no new packages will be installed. Here is my output for the above command:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package 'gcj-4.7-base' is not installed, so not removed
Package 'gcj-4.7-jre' is not installed, so not removed
Package 'openjdk-6-jre-headless' is not installed, so not removed
The following packages will be REMOVED:
  default-jre* icedtea-7-plugin* icedtea-netx* libatk-wrapper-java*
  libatk-wrapper-java-jni* libreoffice-base* minecraft-installer*
  openjdk-7-jre*
0 upgraded, 0 newly installed, 8 to remove and 6 not upgraded.
After this operation, 10,3 MB disk space will be freed.
Do you want to continue [Y/n]? n

But, I don't suggest you to do this. In one day you will need for sure an OpenJDK (6 or 7).

Why this happens

This happens likely because another package on your system is depending on Java. While removing openjdk-7-jre, apt-get sees that if it uninstalls OpenJDK, some packages will have unmet dependencies. To solve this, it installs another package which provides Java.

To find out what is causing this, run these commands in a terminal:

packages=(default-jre default-jre-headless icedtea-6-plugin icedtea-7-plugin java-compiler java-jdk java-runtime java-runtime-headless java-sdk java-virtual-machine java2-jdk java2-runtime java2-runtime-headless java2-sdk java5-jdk java5-runtime java5-runtime-headless java5-sdk java6-jdk java6-runtime java6-runtime-headless java6-sdk java7-jdk java7-runtime java7-runtime-headless java7-sdk openjdk-6-jdk openjdk-6-jre openjdk-6-jre-headless openjdk-7-jdk openjdk-7-jre openjdk-7-jre-headless oracle-java7-bin oracle-java7-fonts oracle-java7-jdk oracle-java7-jre oracle-java7-plugin sun-java6-bin sun-java6-fonts sun-java6-jdk sun-java6-jre sun-java6-plugin)
for pkg in "${packages[@]}"; do
    apt_cache_out="$(apt-cache --installed rdepends "$pkg" | grep -E '^ [| ]\S')"
    if (( $? == 0 )); then
        echo -----------------------
        echo "$pkg"
        echo "$apt_cache_out"
    fi
done

Example output (shortened):

-----------------------
openjdk-7-jre
 |libreoffice-filter-mobiledev
 |libreoffice
 |libreoffice-writer
 |libreoffice-base
 |libreoffice-filter-mobiledev
 |libreoffice
 |libreoffice-writer
 |libreoffice-base

This indicates that all the LibreOffice packages are depending on openjdk-7-jre. As long as these packages are installed, OpenJDK cannot be uninstalled without installing an alternate Java automatically.

To remove openjdk-7-jre

If you want to remove openjdk-7-jre (without installing other packages), you will need to uninstall all packages which depend on it first.

From the example output, that will be:

sudo apt-get remove oracle-java7-installer libreoffice-filter-mobiledev libreoffice libreoffice-writer libreoffice-base libreoffice-filter-mobiledev libreoffice libreoffice-writer libreoffice-base