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Questions[openjdk](ubuntu)

Martin Hope
kerner1000
Asked: 2019-04-24 07:07:44 +0800 CST
  • 19

I installed OpenJDK-11 as described here. I ran sudo apt install openjfx

My java version:

$ java -version
openjdk version "11.0.3" 2019-04-16
OpenJDK Runtime Environment (build 11.0.3+7-Ubuntu-1ubuntu1)
OpenJDK 64-Bit Server VM (build 11.0.3+7-Ubuntu-1ubuntu1, mixed mode, sharing)

But still I get ava.lang.NoClassDefFoundError: javafx/application/Application which indicates that the jre cannot find the FX classes.

java openjdk javafx 19.04
Martin Hope
sancho.s ReinstateMonicaCellio
Asked: 2019-02-28 11:07:43 +0800 CST
  • 13

I have Java 11 and 8 in my Ubuntu 18.04, side by side. I mean to set Java 8 as the default.

What I get:

    $ sudo update-java-alternatives --set /usr/lib/jvm/java-1.8.0-openjdk-amd64
    update-alternatives: error: no alternatives for mozilla-javaplugin.so

    update-java-alternatives: plugin alternative does not exist: /usr/lib/jvm/java-8-openjdk-amd64/lib/IcedTeaPlugin.so

How can I get both plugins if they exist, work.

I am not sure if using (see this)

    sudo update-java-alternative —jre-headless -s java-1.8.0-openjdk-amd64

is ok, so I did not try it. Could it break anything? The Following are results after update-java-alternatives

    $ sudo update-alternatives --config java
    There are 2 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-11-openjdk-amd64/bin/java      1101      auto mode
  1            /usr/lib/jvm/java-11-openjdk-amd64/bin/java      1101      manual mode
* 2            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1081      manual mode

$ java -version
openjdk version "1.8.0_191"
OpenJDK Runtime Environment (build 1.8.0_191-8u191-b12-2ubuntu0.18.04.1-b12)
OpenJDK 64-Bit Server VM (build 25.191-b12, mixed mode)

This is the opposite change from

update-alternatives: error: no alternatives for mozilla-javaplugin.so

https://ubuntuforums.org/showthread.php?t=2402155

Related:

https://serverfault.com/questions/814064/set-jdk-8-as-the-default-java-on-debian-8

java jdk openjdk update-alternatives
Martin Hope
tudor -Reinstate Monica-
Asked: 2018-05-18 21:54:34 +0800 CST
  • 72

While looking to compile OpenJDK from source, the newest General Availability version (OpenJDK 10.0.1) insists on OpenJDK 9 or 10. JDK 11, however, is not due to be released until September 2018.

However, to my surprise, when I do apt search openjdk the result is:

...
openjdk-11-jdk - OpenJDK Development Kit (JDK)
...
openjdk-8-jdk - OpenJDK Development Kit (JDK)
...

No OpenJDK 9 or 10!

And wait, is that OpenJDK 11? Maybe a Beta release? Nooo....

So I looked at apt show openjdk-11-jdk:

Package: openjdk-11-jdk
Version: 10.0.1+10-3ubuntu1
...

Why has OpenJDK 10 been packaged as openjdk-11-*??

package-management versions java openjdk
Martin Hope
OVERTONE
Asked: 2012-02-25 05:07:27 +0800 CST
  • 18

I only recently discovered the different JVM's on the wiki page and thought I'd start tinkering. Its been difficult to find documentation on how to configure Java on Ubuntu though.

Lets say I wanted to change the JRE or JDK that I'm using, I could crack open a terminal and say

sudo update-alternatives --config java

And then pick from one of the installed versions.

If I'm understanding JVM's right (which I may very well be not), You can configure the openJDK to use alternative JVM's (Eg JAMVM) and run it as such

jamvm -jar foo.jar

2 questions,

1: Do i have the concept of a JVM right? As in, is this possible?

2: If so how do i configure the JVM and switch the default to a JVM of my choosing?

java jdk openjdk jre