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, i.e., 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?
type sudo update-alternatives --config java
The select the version you want.
And I think this question should be moved to askubuntu.
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
cd does not change where the shell looks for programs (except when . is in the $PATH). You need to use a full or relative path as in my answer, or change your PATH environment variable to contain the directory first where you want java or javac (or any other executable) to be found.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.