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While installing Android Studio on Ubuntu 14.04 I get the message that my Java version (javac 1.7.0_79) is causing problems. I found a solution of how to install a newer Oracle version of Java:

sudo apt-add-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java8-installer

However I'm afraid that this might overwrite my existing open-jdk version of Java. Since I don't know which of my programs depend on Java, I fear that this could crash these other programs.

Is there a way to make sure apt-get doesn't overwrite my previous Java? I would basically like to have installed both and be able to switch between them manually, depending on what version I need.

fosslinux
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mcExchange
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6 Answers6

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Apt-get won't overwrite the existing java versions.

To switch between installed java versions, use the update-java-alternatives command.

List all java versions:

update-java-alternatives --list

Set java version as default (needs root permissions):

sudo update-java-alternatives --set /path/to/java/version

...where /path/to/java/version is one of those listed by the previous command (e.g. /usr/lib/jvm/java-7-openjdk-amd64).

Additional information:

update-java-alternatives is a convenience tool that uses Debian's alternatives system (update-alternatives) to set a bunch of links to the specified java version (e.g. java, javac, ...).

danzel
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    For me this caused java -version to be java8, but JAVA_HOME was still set to 7 :( – Joel Peltonen Jul 14 '16 at 11:42
  • tq this solve my problem too. @Nenotlep what I did is edit the environment variable manually either in .bashrc or /etc/environment – chrizonline Sep 28 '18 at 09:08
  • update-java-alternatives wasn't available for me. I just replaced that command with update-alternatives java. – nofinator Nov 07 '18 at 21:44
  • @nofinator that only affects the java executable. Which Ubuntu version do you use? – danzel Nov 13 '18 at 08:20
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    @Nenotlep in order to change JAVA_HOME you have to run the following command:

    source /etc/environment

     – janb Nov 16 '18 at 10:23
  • @janb you should edit this answer, as above won't work without your additional input. – Samuel Owino Jun 10 '20 at 12:02
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    @janb I honestly don't understand why this would have any effect unless you manually specified JAVA_HOME in /etc/environment. I just switched back and forth between java 8 and 11, and there is still no JAVA_HOME in /etc/environment. In fact, it is set nowhere in my environment. I therefor rejected the suggested edit. If there are circumstances in which the suggested command is needed, please suggest a new edit and explain when and why it would be necessary. – danzel Jun 10 '20 at 14:24
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    My $JAVA_HOME is unaffected by any of the proposed commands, too. My ~/.bashrc has a line export JAVA_HOME=$(readlink -f /usr/bin/javac | sed "s:bin/javac::") though and that does the trick for me: source ~/.bashrc. If your ~/.bashrc doesn't have that line, run directly export JAVA_HOME=$(readlink -f /usr/bin/javac | sed "s:bin/javac::"). – Giszmo Jun 18 '20 at 14:27
  • This easily did the work in my PopOS! Thanks a lot @danzel – Akhil Sep 26 '21 at 06:02
151

Use

sudo update-alternatives --config java

which lists all installed versions with current active one marked and provides dialog to switch:

There are 3 choices for the alternative java (providing /usr/bin/java).

Selection    Path...
------------------------------------------------------------
  0            /usr/lib/jvm/java-9-oracle/bin/java...
* 1            /usr/lib/jvm/java-7-oracle/jre/bin/java...
  2            /usr/lib/jvm/java-8-oracle/jre/bin/java...
  3            /usr/lib/jvm/java-9-oracle/bin/java...

Press <enter> to keep...[*], or type selection number:

Use

export JAVA_HOME="$(jrunscript -e 'java.lang.System.out.println(java.lang.System.getProperty("java.home"));')"

to set $JAVA_HOME from current active version

muet
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    As noted by @danzel at the accepted answer, this affects only the java executable, not the other parts of the configuration. Use update-java-alternatives if available. – Premek Brada Jan 10 '19 at 20:59
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    Using this command, you have to update each of java, javac & jrunscript separately. – Stewart Mar 16 '20 at 10:19
20

Configuring Java

You can configure which version is the default for use in the command line by using update-alternatives, which manages which symbolic links are used for different commands.

sudo update-alternatives --config java

The output will look something like the following.

There are 5 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1081      auto mode
  1            /usr/lib/jvm/java-6-oracle/jre/bin/java          1         manual mode
  2            /usr/lib/jvm/java-7-oracle/jre/bin/java          2         manual mode
  3            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1081      manual mode
  4            /usr/lib/jvm/java-8-oracle/jre/bin/java          3         manual mode
  5            /usr/lib/jvm/java-9-oracle/bin/java              4         manual mode

Press <enter> to keep the current choice[*], or type selection number:

You can now choose the number to use as a default. This can also be done for other Java commands, such as the compiler (javac), the documentation generator (javadoc), the JAR signing tool (jarsigner), and more. You can use the following command, filling in the command you want to customize.

sudo update-alternatives --config command

Setting the JAVA_HOME Environment Variable

Many programs, such as Java servers, use the JAVA_HOME environment variable to determine the Java installation location.

Copy the path from your preferred installation and then open /etc/environment using Sublime Text or your favourite text editor.

sudo subl /etc/environment

At the end of this file, add the following line, making sure to replace the highlighted path with your own copied path.

JAVA_HOME="/usr/lib/jvm/java-8-oracle"

Save and exit the file, and reload it: source /etc/environment.
You can now test whether the environment variable has been set by executing the following command: echo $JAVA_HOME. This will return the path you just set.

naXa stands with Ukraine
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11

Based on the answer from @muet, I found this to work seamlessly:

Add this to ~/.bashrc:

export JAVA_HOME="$(jrunscript -e 'java.lang.System.out.println(java.lang.System.getProperty("java.home"));')"

Add to aliases:

alias useJava8='yes | sudo apt-get install oracle-java8-set-default && source ~/.bashrc'
alias useJava7='yes | sudo apt-get install oracle-java7-set-default && source ~/.bashrc'

Then you can switch within the same shell using only: useJava7or useJava8

Zanna
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brianjohnsen
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  • to make aliases permanent one can put them in ~/.bashrc , more info here https://askubuntu.com/questions/17536/how-do-i-create-a-permanent-bash-alias – Konstantin Ziubin Feb 05 '18 at 14:01
  • E: Unable to locate package oracle-java7-set-default – Prakash P Mar 27 '18 at 12:19
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    The unequivocally easiest way to install, use, and switch between different java versions is using SDKMAN!

    See here: http://sdkman.io/usage.html

     – brianjohnsen Mar 28 '18 at 12:51
  • recently come across another command to set the JAVA_HOME, yet to try on .bashrc: export JAVA_HOME=$(dirname $(dirname $(readlink -f $(which java)))) – ThiamTeck Dec 08 '18 at 02:53
  • oracle-java package does not exist. Use openjdk-8-jdk https://docs.datastax.com/en/jdk-install/doc/jdk-install/installOpenJdkDeb.html – GilbertS Nov 10 '20 at 15:28
1

Consider also using the GUI tool galternatives available through the ubuntu package manager.

mapto
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0

jrunscriptmay not be available in future releases, so safe choice is using export JAVA_HOME=$(dirname $(dirname $(readlink -f $(which java)))) as suggested by @ThiamTeck. Also .bashrc needs to be executed every time you change your java version using update-alternative command.

Rahul Chandak
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