How to completely uninstall Java?

1. Remove all the Java related packages (Sun, Oracle, OpenJDK, IcedTea plugins, GIJ):

   dpkg-query -W -f='${binary:Package}\n' | grep -E -e '^(ia32-)?(sun|oracle)-java' -e '^openjdk-' -e '^icedtea' -e '^(default|gcj)-j(re|dk)' -e '^gcj-(.*)-j(re|dk)' -e '^java-common' | xargs sudo apt-get -y remove
   sudo apt-get -y autoremove
   

2. Purge config files (careful. This command removed libsgutils2-2 and virtualbox config files too):

   dpkg -l | grep ^rc | awk '{print($2)}' | xargs sudo apt-get -y purge
   

3. Remove Java config and cache directory:

   sudo bash -c 'ls -d /home/*/.java' | xargs sudo rm -rf
   

4. Remove manually installed JVMs:

   sudo rm -rf /usr/lib/jvm/*
   

5. Remove Java entries, if there is still any, from the alternatives:

   for g in ControlPanel java java_vm javaws jcontrol jexec keytool mozilla-javaplugin.so orbd pack200 policytool rmid rmiregistry servertool tnameserv unpack200 appletviewer apt extcheck HtmlConverter idlj jar jarsigner javac javadoc javah javap jconsole jdb jhat jinfo jmap jps jrunscript jsadebugd jstack jstat jstatd native2ascii rmic schemagen serialver wsgen wsimport xjc xulrunner-1.9-javaplugin.so; do sudo update-alternatives --remove-all $g; done
   

6. Search for possible remaining Java directories:

   sudo updatedb
   sudo locate -b '\pack200'
   

   If the command above produces any output like /path/to/jre1.6.0_34/bin/pack200 remove the directory that is parent of bin, like this: sudo rm -rf /path/to/jre1.6.0_34.

To completely remove OpenJDK on Ubuntu 11.10 (this may or may not be sufficient on other versions of Ubuntu), run:

sudo apt-get purge openjdk-\* icedtea-\* icedtea6-\*

If you want instructions for removing the proprietary Oracle ("Sun") version of Java, then you'll have to specify how you installed it. (If you edit your question to indicate this and leave a comment to this answer, I'll try to add information about how to remove that too.)

To uninstall Oracle Java 7, just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command below.

sudo update-alternatives --display java

To check the setup before uninstalling Java.

Next, remove symlinks

(replace the word (version)with your Java version. DO java -version to get yours. So if your version is 1.7.0_03, you would type sudo update-alternatives --remove "java" "/usr/lib/jvm/jdk1.7.0_03/bin/java")

sudo update-alternatives --remove "java" "/usr/lib/jvm/jdk<version>/bin/java"
sudo update-alternatives --remove "javac" "/usr/lib/jvm/jdk<version>/bin/javac"
sudo update-alternatives --remove "javaws" "/usr/lib/jvm/jdk<version>/bin/javaws"

verify that the symlinks were removed

java -version
javac -version
which javaws

The next 2 commands must be type excatly perfectly to avoid permanently destroying your system.

cd /usr/lib/jvm
sudo rm -rf jdk<version>

Then do

sudo update-alternatives --config java
sudo update-alternatives --config javac
sudo update-alternatives --config javaws

Then do

sudo vi  /etc/environment

Delete the line with JAVA_HOME ¹

To uninstall OpenJDK (if installed). First check which OpenJDK packages are installed.

sudo dpkg --list | grep -i jdk

To remove openjdk:

sudo apt-get purge openjdk*

Uninstall OpenJDK related packages.

sudo apt-get purge icedtea-* openjdk-*

Check that all OpenJDK packages have been removed.

sudo dpkg --list | grep -i jdk

^{1Source:akbarahmed.com}

You may not need to completely remove the OpenJDK to resolve your problem. Install the sun-java6 packages. Then use update-java-alternatives to switch to the Sun java packages.

If you do want to completely remove OpenJDK remove the default-jdk and/or default-jre packages. You may need to remove some java packages but most of them should be happy once you have the Sun JDK packages installed.

You may want to follow one of these cleanup tips once you are done removing packages.

Try this command:

java -version

If 1.6* comes then try:

sudo apt-get autoremove openjdk-6-jre

If 1.7* comes then try:

sudo apt-get autoremove openjdk-7-jre

Assuming that you don't have jdk in your system. If you have use this command:

sudo apt-get autoremove openjdk-`<version>`-jdk

replace with the version like we did it in previous example.

easier is to use synaptic.

click tab "sections" scroll down to java. simply select each item you see with green box and mark for complete removal. repeat for all all java sections and all files.

Agreed with Eliah. "apt-get purge" command can remove those packages completely.

Assuming you have previously installed a copy of java-6-sun package, a followup will help getting rid of broken symbolic link:

sudo update-alternatives --config java

And then select a correct path which you want to link up as default Java calling path.

Then have a check on the version of Java with this command:

java -version

Just remove all files of JDK or JRE, for example it's usually installed in this location:

/usr/lib/jvm/java-7-oracle

So remove all files resides in "java-7-oracle" folder with root permission and extract the latest JDK or JRE files in it. That's it now you would have the latest Java version Installed.

P.S. Your directory name may differ from java-7-oracle.

Reference: Official installation instruction from Oracle