How to set JAVA path to JDK 8

Question

Was trying to contribute to some open-source project. And I tried finding the answer online, tried Wikipedia how to set it. None works. This is getting irritating. I need to commit my work. As I run git commit here is what I get:

please make sure JAVA_HOME is set to JDK8

Now, I use JAVA 11. I uninstalled JAVA 11 then tried installing JAVA 8. No success, tried installing 12 again JDK8 is needed.

echo $JAVA_HOME

gives

/usr/lib/jvm/java-12-oracle

java -version

is 12.0.2

I want to install Java 8 and Java 12 both on my computer. And frequently shift between two. I want to be able to work on projects which work with java 8 and those which work with java 12.

dpkg -L openjdk-8-jdk

Gives

/.
/usr
/usr/lib
/usr/lib/jvm
/usr/lib/jvm/java-8-openjdk-amd64
/usr/lib/jvm/java-8-openjdk-amd64/bin
/usr/lib/jvm/java-8-openjdk-amd64/bin/appletviewer
/usr/lib/jvm/java-8-openjdk-amd64/bin/jconsole
/usr/lib/jvm/java-8-openjdk-amd64/include
/usr/lib/jvm/java-8-openjdk-amd64/include/jawt.h
/usr/lib/jvm/java-8-openjdk-amd64/include/linux
/usr/lib/jvm/java-8-openjdk-amd64/include/linux/jawt_md.h
/usr/lib/jvm/java-8-openjdk-amd64/lib
/usr/lib/jvm/java-8-openjdk-amd64/lib/jconsole.jar
/usr/lib/jvm/java-8-openjdk-amd64/man
/usr/lib/jvm/java-8-openjdk-amd64/man/ja_JP.UTF-8
/usr/lib/jvm/java-8-openjdk-amd64/man/ja_JP.UTF-8/man1
/usr/lib/jvm/java-8-openjdk-amd64/man/ja_JP.UTF-8/man1/appletviewer.1.gz
/usr/lib/jvm/java-8-openjdk-amd64/man/ja_JP.UTF-8/man1/jconsole.1.gz
/usr/lib/jvm/java-8-openjdk-amd64/man/man1
/usr/lib/jvm/java-8-openjdk-amd64/man/man1/appletviewer.1.gz
/usr/lib/jvm/java-8-openjdk-amd64/man/man1/jconsole.1.gz
/usr/share
/usr/share/doc
/usr/share/doc/openjdk-8-jre-headless
/usr/share/doc/openjdk-8-jre-headless/test-amd64
/usr/share/doc/openjdk-8-jre-headless/test-amd64/check-hotspot-hotspot.log.gz
/usr/share/doc/openjdk-8-jre-headless/test-amd64/check-jdk-hotspot.log.gz
/usr/share/doc/openjdk-8-jre-headless/test-amd64/check-langtools-hotspot.log.gz
/usr/share/doc/openjdk-8-jre-headless/test-amd64/failed_tests-hotspot.tar.gz
/usr/share/doc/openjdk-8-jre-headless/test-amd64/jtreg-summary-hotspot.log.gz
/usr/share/doc/openjdk-8-jre-headless/test-amd64/jtreport-hotspot.tar.gz
/usr/share/doc/openjdk-8-jdk

Solution

You can use "alternatives" to switch between different java versions:

sudo update-alternatives --config java

And also for the java compiler (javac) if you are compiling some java code:

sudo update-alternatives --config javac

If you installed Java 8 from apt openjdk:

sudo apt install openjdk-8-jdk

Then your java home must be: /usr/lib/jvm/java-8-openjdk-amd64

export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64

If java 8 is not visible in update-alternatives you can install it with:

update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-8-openjdk-amd64/bin/java 1000

Then check it's there with:

update-alternatives --list java

Comments

[Rishabh]

/usr/lib/jvm/java-8-openjdk-amd64 : There is no such directory it is showing.

[Radhwane Chebaane]

yes, JAVA_HOME is a directory not a file. It points to the root directory contianing Java install files.

[Rishabh]

sudo update-alternatives --config java shows me only java12. But when I do sudo apt install openjdk-8-jdk. It says openjdk-8-jdk is already the newest version, that means jdk 8 is already installed

[Radhwane Chebaane]

Then you probably need to tell update-alternatives where is installed the java 8: update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1000

[Rishabh]

it is showing me error: alternative path /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java doesn't exist

[Rishabh]

I ran : update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1000

[Rishabh]

Further $JAVA_HOME gives me : bash: /usr/lib/jvm/jdk1.8.0: No such file or directory

[Radhwane Chebaane]

If you successfully installed openjdk-8-jdk, could you give me the output of this command ? dpkg -L openjdk-8-jdk

[Rishabh]

I have edited the question.

[Radhwane Chebaane]

Ok, try to set java8 again into alternatives: update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-8-openjdk-amd64/bin/java 1000 Then check it's there with: update-alternatives --config java

[Rishabh]

Again, it is showing me update-alternatives: error: alternative path /usr/lib/jvm/java-8-openjdk-amd64/bin/java doesn't exist

[Radhwane Chebaane]

If file /usr/lib/jvm/java-8-openjdk-amd64/bin/java does not exist, then you must reinstall java again: apt purge java* openjdk* apt install openjdk-8-jdk If you still need java 11 install openjdk-11-jdk

[Rishabh]

This is causing me headaches. sudo apt purge java* openjdk* don't work this causes. sudo apt install openjdk-8-jdk to show me no new installation.