Home / ubuntu / Questions / 740757
Accepted
mcExchange
Asked: 2016-03-02 02:05:08 +0800 CST

Switch between multiple java versions

  • 772

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.

java

6 Answers

  1. Best Answer

    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, ...).

    • 180

  2. 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

    • 121

  3. 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.

    • 14

  4. 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

    • 11

  5. 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.

    • 0

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

    • 0