Ubuntu – Update-java-alternatives vs update-alternatives –config java


On Ubuntu 12.04 LTS I have installed Sun's JDK7, Eclipse, and the Arduino IDE. I want the Arduino to use OpenJDK 6 and want Eclipse to use Sun's JDK 7.

From my understanding I need to manually choose which Java to use before running each application. This led me to the update-java-alternatives -l command. When I run this I only see the following:

java-1.6.0-openjdk-amd64 1061 /usr/lib/jvm/java-1.6.0-openjdk-amd64

but when I run update-alternatives --config java I see the following:

*0  /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java   auto mode
1  /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java   manual mode
2  /usr/lib/jvm/jdk1.7.0/bin/java                   manual mode
3  /usr/lib/jvm/jre1.7.0/bin/java                   manual mode

I don't understand why the update-java-alternatives doesn't display the same 3 options. I also don't understand how to switch between OpenJDK6 and JDK7. How I can go about using the OpenJDK6 for Arduino development and Sun JDK7 for Eclipse/Android development?

Best Answer

  • sudo update-alternatives --config java

    Configures the default for the program "java". That's the Java VM.

    sudo update-alternatives --config javac

    Configures the default Java compiler.

    You can also see that, because the first command lists a lot of "JRE" (Java Runtime Environment) folders and the Program is just called "java".

    If I check which version is being used by issuing the command java -version or javac -version, I can see, that each command changes the program being used.

    However, using update-java-alternatives with a JDK Version changes both programs for me. Using the first commands, you can use a Java VM and Java Compiler from different JDKs.

    update-java-alternatives requires presence of a file with extension .jinfo in directory /usr/lib/jvm. The opendjk package is shipped with a .jinfo file, the jdk of Oracle (formerly Sun) is not. As alternative, you configure alternatives without update-java-alternatives:

    For example, to add java from jvm-directory /usr/lib/jvm/jdk-12.0.1 (default directory of Debian package of Oracle) with priority 2082, use the following command:

    sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk-12.0.1/bin/java 2082

    As for switching for different development environments:

    Are you talking about starting the IDE itself with different Java versions or using different versions in the IDE for compilation and running your app?

    For 1.: You can specify which JVM to use in the eclipse.ini, as described here. I don't know how to do that for the Arduino IDE.

    For 2.: In Eclipse you can select the JRE/JDK to be used in Window -> Preferences -> Java -> Installed JREs. And under Java -> Compiler you could choose an older Java compliance if you wish.

    EDIT: This DigitalOcean page also has a very nice explanation of everything related to Java on Ubuntu.

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