在 Ubuntu 中使用多个版本的 Java

Question

I have a Ubuntu machine where I already have one JDK version which is installed. Next I have downloaded the second version into /usr/local .

Now, I want to run a program against the second JDK which is in /usr/local , ie, I will copy a sample .java program in /usr/local/bin and then execute it.

But the problem is, even If I navigate to the /usr/local/bin and type $ java -version , I am getting the one which is installed in the first place. Is there any solution for this?

Answer 1

type sudo update-alternatives --config java

The select the version you want.

And I think this question should be moved to askubuntu .

Answer 2

When you run java with no path, then your shell looks in your $PATH environment variable to find java . If you want a specific java , you need to either change your $PATH , or run it with a path, like:

/usr/local/bin/java

or if you really want to cd there first, you could run

./java

from /usr/local/bin

Answer 3

Here's an approach tested on Ubuntu 20.04 which shows adjusting the javac and java defaults:

$ sudo apt install openjdk-14-jdk
$ sudo apt install openjdk-8-jdk
$ java -version
openjdk version "14.0.2" 2020-07-14
OpenJDK Runtime Environment (build 14.0.2+12-Ubuntu-120.04)
OpenJDK 64-Bit Server VM (build 14.0.2+12-Ubuntu-120.04, mixed mode, sharing)
$ javac -version
javac 14.0.2
$ update-java-alternatives --list
java-1.14.0-openjdk-amd64      1411       /usr/lib/jvm/java-1.14.0-openjdk-amd64
java-1.8.0-openjdk-amd64       1081       /usr/lib/jvm/java-1.8.0-openjdk-amd64
$ 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-14-openjdk-amd64/bin/java      1411      auto mode
  1            /usr/lib/jvm/java-14-openjdk-amd64/bin/java      1411      manual mode
  2            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1081      manual mode

Press <enter> to keep the current choice[*], or type selection number: 2
update-alternatives: using /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java to provide /usr/bin/java (java) in manual mode
$ sudo update-alternatives --config javac
There are 2 choices for the alternative javac (providing /usr/bin/javac).

  Selection    Path                                          Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-14-openjdk-amd64/bin/javac   1411      auto mode
  1            /usr/lib/jvm/java-14-openjdk-amd64/bin/javac   1411      manual mode
  2            /usr/lib/jvm/java-8-openjdk-amd64/bin/javac    1081      manual mode

Press <enter> to keep the current choice[*], or type selection number: 2
update-alternatives: using /usr/lib/jvm/java-8-openjdk-amd64/bin/javac to provide /usr/bin/javac (javac) in manual mode
$ java -version
openjdk version "1.8.0_275"
OpenJDK Runtime Environment (build 1.8.0_275-8u275-b01-0ubuntu1~20.04-b01)
OpenJDK 64-Bit Server VM (build 25.275-b01, mixed mode)
$ javac -version
javac 1.8.0_275

See Switch between multiple java versions on askubuntu for a canonical thread.