Change JAVA_HOME in docker

Change JAVA_HOME in docker - java

The legacy web application which I want to dockerise uses some old classes like com/sun/image/codec/jpeg/ImageFormatException which were supported till Java SE7.
Now in the docker container default jdk getting (on installing tomcat-6 container) is
java version "1.7.0_131"
OpenJDK Runtime Environment (IcedTea 2.6.9) (7u131-2.6.9-2~deb8u1)
OpenJdk doesn't support these classes
I used update-alternatives to install Oracle Jdk7.80
After loading container, on giving java -version I am getting
java version "1.7.0_80"
Java(TM) SE Runtime Environment (build 1.7.0_80-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.80-b11, mixed mode)
However, echo $JAVA_HOME after entering the container gives /docker-java-home/jre which again points to OpenJdk. How can I set JAVA_HOME to the Oracle Jdk home that I installed?

You can simply set/change environment variables of your docker image by using the ENV command in your Dockerfile:
ENV JAVA_HOME /path/to/java

If your base image contains by default OpenJDK and If you want to use OracleJDK in your image just add the below command to your dockerfile and build the image and boom your image will have oracle JDK.
RUN yum -y remove java***
RUN yum localinstall -y jdk-8u212-linux-x64.rpm && \
echo "JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:bin/java::")" | tee
-a /etc/profile && source /etc/profile && echo $JAVA_HOME && \
rm jdk-8u212-linux-x64.rpm && \
alternatives --set java /usr/java/jdk1.8.0_212-amd64/jre/bin/java

Related

Java version can't be switch in MAC os it always set 1.6.0 like default [duplicate]

How can you change the default version of Java on a mac?

First run /usr/libexec/java_home -V which will output something like the following:
Matching Java Virtual Machines (3):
1.8.0_05, x86_64: "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0_05.jdk/Contents/Home
1.6.0_65-b14-462, x86_64: "Java SE 6" /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
1.6.0_65-b14-462, i386: "Java SE 6" /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
/Library/Java/JavaVirtualMachines/jdk1.8.0_05.jdk/Contents/Home
Pick the version you want to be the default (1.6.0_65-b14-462 for arguments sake) then:
export JAVA_HOME=`/usr/libexec/java_home -v 1.6.0_65-b14-462`
or you can specify just the major version, like:
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`
Now when you run java -version you will see:
java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-462-11M4609)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-462, mixed mode)
Add the export JAVA_HOME… line to your shell’s init file.
For Bash (as stated by antonyh):
export JAVA_HOME=$(/usr/libexec/java_home -v 1.8)
For Fish (as stated by ormurin)
set -x JAVA_HOME (/usr/libexec/java_home -d64 -v1.8)
Updating the .zshrc file should work:
nano ~/.zshrc
export JAVA_HOME=$(/usr/libexec/java_home -v 1.8.0)
Press CTRL+X to exit the editor
Press Y to save your changes
source ~/.zshrc
echo $JAVA_HOME
java -version

This answer is an attempt to address: how to control java version system-wide (not just in currently running shell) when several versions of JDK are installed for development purposes on macOS El Capitan or newer (Sierra, High Sierra, Mojave). As far as I can tell, none of the current answers do that (*).
As a developer, I use several JDKs, and I want to switch from one to the other easily. Usually I have the latest stable one for general use, and others for tests. But I don't want the system (e.g. when I start my IDE) to use the latest "early access" version I have for now. I want to control system's default, and that should be latest stable.
The following approach works with Java 7 to 12 at least (early access at the time of this writing), with Oracle JDK or OpenJDK (including builds by AdoptOpenJDK produced after mid-October 2018).
Solution without 3rd party tools:
leave all JDKs at their default location, under /Library/Java/JavaVirtualMachines. The system will pick the highest version by default.
To exclude a JDK from being picked by default, rename its Contents/Info.plist to Info.plist.disabled. That JDK can still be used when $JAVA_HOME points to it, or explicitly referenced in a script or configuration. It will simply be ignored by system's java command.
System launcher will use the JDK with highest version among those that have an Info.plist file.
When working in a shell with alternate JDK, pick your method among existing answers (jenv, or custom aliases/scripts around /usr/libexec/java_home, etc).
Details of investigation in this gist.
(*) Current answers are either obsolete (no longer valid for macOS El Capitan or Sierra), or only address a single JDK, or do not address the system-wide aspect. Many explain how to change $JAVA_HOME, but this only affects the current shell and what is launched from there. It won't affect an application started from OS launcher (unless you change the right file and logout/login, which is tedious). Same for jenv, it's cool and all, but as far as I can tell it merely changes environment variables, so it has the same limitation.

Adding to the above answers, I put the following lines in my .bash_profile (or .zshrc for MacOS 10.15+) which makes it really convenient to switch (including #elektromin's comment for java 9):
alias j12="export JAVA_HOME=`/usr/libexec/java_home -v 12`; java -version"
alias j11="export JAVA_HOME=`/usr/libexec/java_home -v 11`; java -version"
alias j10="export JAVA_HOME=`/usr/libexec/java_home -v 10`; java -version"
alias j9="export JAVA_HOME=`/usr/libexec/java_home -v 9`; java -version"
alias j8="export JAVA_HOME=`/usr/libexec/java_home -v 1.8`; java -version"
alias j7="export JAVA_HOME=`/usr/libexec/java_home -v 1.7`; java -version"
After inserting, execute $ source .bash_profile
I can switch to Java 8 by typing the following:
$ j8
java version "1.8.0_102"
Java(TM) SE Runtime Environment (build 1.8.0_102-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.102-b14, mixed mode)

A small fish function based on /usr/libexec/java_home
function jhome
set JAVA_HOME (/usr/libexec/java_home $argv)
echo "JAVA_HOME:" $JAVA_HOME
echo "java -version:"
java -version
end
If you don't use fish, you can do something similar in bash:
#!/bin/bash
jhome () {
export JAVA_HOME=`/usr/libexec/java_home $#`
echo "JAVA_HOME:" $JAVA_HOME
echo "java -version:"
java -version
}
Then to switch between javas do:
$> jhome #switches to latest java
$> jhome -v 1.7 #switches to java 1.7
$> jhome -v 1.6 #switches to java 1.6
ref: https://gist.github.com/kenglxn/1843d552dff4d4233271

Update...
With macOS Monterey, v12.0.1 Cask is no longer a Brew command. Just follow the steps but in step 4 just do $ brew install ... or $ brew install --cask ... instead of $ brew cask install ... Thanks to #Shivam Sahil comment.
I will share my experiences with macOS Big Sur v11.4, the best way to deal with these problems is by installing java using Homebrew:
1 - Install Homebrew.
$ ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
2 - Install Homebrew Cask.
$ brew tap homebrew/cask-versions
$ brew update
$ brew tap homebrew/cask
3 - Install the latest version of Java
$ brew cask install java
4 - Install the other needed versions of Java (Java8, Java11, Java13).
$ brew tap adoptopenjdk/openjdk
$ brew cask install adoptopenjdk8
$ brew cask install adoptopenjdk11
$ brew cask install adoptopenjdk13
$ brew cask install adoptopenjdk14
5 - Switch between different versions of Java
Switching between different versions of Java, you only need to add the following to your .bash_profile or .zshrc.
In this case, we want to be able to switch between Java8, Java11, Java13 and Java14:
export JAVA_8_HOME=$(/usr/libexec/java_home -v1.8)
export JAVA_11_HOME=$(/usr/libexec/java_home -v11)
export JAVA_13_HOME=$(/usr/libexec/java_home -v13)
export JAVA_14_HOME=$(/usr/libexec/java_home -v14)
alias java8='export JAVA_HOME=$JAVA_8_HOME'
alias java11='export JAVA_HOME=$JAVA_11_HOME'
alias java13='export JAVA_HOME=$JAVA_13_HOME'
alias java14='export JAVA_HOME=$JAVA_14_HOME'
# default to Java 14
java14
6 - Reload .bash_profile or .zshrc for the aliases to take effect:
$ source ~/.bash_profile
or
$ source ~/.zshrc
7 - Finally you can use the aliases to switch between different Java versions.
$ java8
$ java -version
java version "1.8.0_261"
For more info you can see this post: How to Use Brew to Install Java on Mac

Use jenv is an easy way. (Update 2022)
Install jenv: see Getting started
Install java with brew
brew install openjdk#11
ln -s /usr/local/opt/openjdk#11/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk-11.jdk
#other java
brew install openjdk#8
brew install openjdk#17
Add java to jenv
jenv add /Library/Java/JavaVirtualMachines/openjdk-11.jdk/Contents/Home
Use: refer to jenv

It is a little bit tricky, but try to follow the steps described in Installing Java on OS X 10.9 (Mavericks). Basically, you gonna have to update your alias to java.
Step by step:
After installing JDK 1.7, you will need to do the sudo ln -snf in order to change the link to current java. To do so, open Terminal and issue the command:
sudo ln -nsf /Library/Java/JavaVirtualMachines/jdk1.7.0_51.jdk/Contents \
/System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK
Note that the directory jdk1.7.0_51.jdk may change depending on the SDK version you have installed.
Now, you need to set JAVA_HOME to point to where jdk_1.7.0_xx.jdk was installed. Open again the Terminal and type:
export JAVA_HOME="/Library/Java/JavaVirtualMachines/jdk1.7.0_51.jdk/Contents/Home"
You can add the export JAVA_HOME line above in your .bashrc file to have java permanently in your Terminal

install JDK, not just JRE
/usr/libexec/java_home -v 1.8
gives
/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home
next
touch .bash_profile
open -a TextEdit.app .bash_profile
TextEdit will show you a blank page which you can fill in.
add to doc:
export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home
in terminal:
export JAVA_HOME="$(/usr/libexec/java_home -v 1.8)"
try the command:
javac -version
should output:
javac 1.8.0_111

tl;dr
Add the line:
export JAVA_HOME='/Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home'
to the file
~/.bash_profile
(replace jdk1.8.0_144.jdk with your downloaded version)
then source ~/.bash_profile

Use jenv, it is like a Java environment manager. It is super easy to use and clean
For Mac, follow the steps:
brew install jenv
git clone https://github.com/gcuisinier/jenv.git ~/.jenv
Installation: If you are using bash follow these steps:
$ echo 'export PATH="$HOME/.jenv/bin:$PATH"' >> ~/.bash_profile
echo 'eval "$(jenv init -)"' >> ~/.bash_profile
$ exec $SHELL -l
Add desired versions of JVM to jenv:
jenv add /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
jenv add /System/Library/Java/JavaVirtualMachines/1.8.0.jdk/Contents/Home
Check the installed versions:
jenv versions
Set the Java version you want to use by:
jenv global oracle64-1.6.0

Four easy steps using terminal for people who uses the default process.. :)
echo $JAVA_HOME gives you current java home. For eg: /Library/Java/JavaVirtualMachines/jdk1.8.0_191.jdk/Contents/Home/
cd /Library/Java/JavaVirtualMachines/ will take you to the folder where u normally install jdks (It might be different for your machines)
ls shows you available folders (normally it will have the version numbers, for eg: jdk1.8.0_191.jdk openjdk-11.0.2.jdk)
export JAVA_HOME='/Library/Java/JavaVirtualMachines/openjdk-11.0.2.jdk/Contents/Home' will change the java home..

Consider the following approach only to change the JDK for each and specific tab of your terminal (i.e: iTerm).
Having in the /Library/Java/JavaVirtualMachines path the two following jdks
openjdk8u275-b01
openjdk-11.0.9.1+1
And in the .bash_profile file the following:
export JAVA_HOME=/Library/Java/JavaVirtualMachines/openjdk-11.0.9.1+1/Contents/Home
export PATH=$JAVA_HOME/bin:$PATH
If you open Iterm - with the first Tab A - and the following commands are executed:
javac -version
javac 11.0.9.1
java -version
openjdk version "11.0.9.1" 2020-11-04
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.9.1+1)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.9.1+1, mixed mode)
The output is correct and expected
But if you open a second Tab B and you need override the default JDK then write in the terminal the following:
export JAVA_HOME=/Library/Java/JavaVirtualMachines/openjdk8u275-b01/Contents/Home/
export PATH=$JAVA_HOME/bin:$PATH
Then
javac -version
javac 1.8.0_275
java -version
openjdk version "1.8.0_275"
OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_275-b01)
OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.275-b01, mixed mode)
It works fine. Of course if the Tab B is closed or you open a new Tab C all work according the .bash_profile settings (therefore the default settings)

macOS El Capitan or newer will choose the higher version of the JDK available in /Library/Java/JavaVirtualMachines, so in order to downgrade you may rename the file Info.plist to something else like Info.plist.disabled so that the OS will choose a previous version.

function setjdk() {
if [ $# -ne 0 ]; then
removeFromPath '/System/Library/Frameworks/JavaVM.framework/Home/bin'
if [ -n "${JAVA_HOME+x}" ]; then
removeFromPath $JAVA_HOME
fi
export JAVA_HOME=`/usr/libexec/java_home -v $#`
export PATH=$JAVA_HOME/bin:$PATH
fi
}
put this in your ~/.profile and use it in your terminal like so setjdk 1.8, setjdk 1.7, setjdk 9 etc etc...
If you don't have removeFromPath then it is:
function removeFromPath() {
export PATH=$(echo $PATH | sed -E -e "s;:$1;;" -e "s;$1:?;;")
}

You can add it to your .bash_profile to have the version set by default.
//Open bash profile
open ~/.bash_profile
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`
// run bash profile
source ~/.bash_profile

add following command to the ~/.zshenv file
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`

Add following in your ~/.bash_profile and set the default java version accordingly.
export JAVA_8_HOME=$(/usr/libexec/java_home -v1.8)
export JAVA_11_HOME=$(/usr/libexec/java_home -v11)
alias java8='export JAVA_HOME=$JAVA_8_HOME'
alias java11='export JAVA_HOME=$JAVA_11_HOME'
# default to Java 8
java8
I am using macOS and have installed java using brew.
Edit:
If you are not using bash please update the correct shell file, example, if you are using zsh then it will be ~/.zshrc

Add the following line of code to your .zshrc (or bash_profile):
alias j='f(){ export JAVA_HOME=/usr/libexec/java_home -v $1 };f'
Save to session:
$ source .zshrc
Run command (e.g. j 13, j14, j1.8...)
$ j 1.8
Explanation
This is parameterised so you do not need to update the script like other solutions posted. If you do not have the JVM installed you are told. Sample cases below:
/Users/user/IDE/project $ j 1.8
/Users/user/IDE/project $ java -version
openjdk version "1.8.0_265"
OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_265-b01)
OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.265-b01, mixed mode)
/Users/user/IDE/project $ j 13
/Users/user/IDE/project $ java -version
openjdk version "13.0.2" 2020-01-14
OpenJDK Runtime Environment (build 13.0.2+8)
OpenJDK 64-Bit Server VM (build 13.0.2+8, mixed mode, sharing)
/Users/user/IDE/project $ j 1.7
Unable to find any JVMs matching version "1.7".

Check Java version: java -version
Switch between versions: https://devqa.io/brew-install-java/
open ~/.bash_profile
export JAVA_8_HOME=$(/usr/libexec/java_home -v1.8)
export JAVA_11_HOME=$(/usr/libexec/java_home -v11)
alias java8='export JAVA_HOME=$JAVA_8_HOME'
alias java11='export JAVA_HOME=$JAVA_11_HOME'
source ~/.bash_profile
When we are switching to java11 or java8, java -version command is not showing the correct version.
In that case use mvn -version to see the correct java version is used for building the solution

From the Apple's official java_home(1) man page:
**USAGE**
/usr/libexec/java_home helps users set a $JAVA_HOME in their login rc files, or provides a way for
command-line Java tools to use the most appropriate JVM which can satisfy a minimum version or archi-
tecture requirement. The --exec argument can invoke tools in the selected $JAVA_HOME/bin directory,
which is useful for starting Java command-line tools from launchd plists without hardcoding the full
path to the Java command-line tool.
Usage for bash-style shells:
$ export JAVA_HOME=`/usr/libexec/java_home`
Usage for csh-style shells:
% setenv JAVA_HOME `/usr/libexec/java_home`

JDK Switch Script
I have adapted the answer from #Alex above and wrote the following to fix the code for Java 9.
$ cat ~/.jdk
#!/bin/bash
#list available jdks
alias jdks="/usr/libexec/java_home -V"
# jdk version switching - e.g. `jdk 6` will switch to version 1.6
function jdk() {
echo "Switching java version $1";
requestedVersion=$1
oldStyleVersion=8
# Set the version
if [ $requestedVersion -gt $oldStyleVersion ]; then
export JAVA_HOME=$(/usr/libexec/java_home -v $1);
else
export JAVA_HOME=`/usr/libexec/java_home -v 1.$1`;
fi
echo "Setting JAVA_HOME=$JAVA_HOME"
which java
java -version;
}
Switch to Java 8
$ jdk 8
Switching java version 8
Setting JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home
/usr/bin/java
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)
Switch to Java 9
$ jdk 9
Switching java version 9
Setting JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home
/usr/bin/java
java version "9.0.1"
Java(TM) SE Runtime Environment (build 9.0.1+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)

If still u are not able to set it. using this command.
export JAVA_HOME=/usr/libexec/java_home -v 1.8
then you have to use this one.
export JAVA_HOME=$(/usr/libexec/java_home -v 1.8)
it will surely work.

First find out where do you store the environment variables-
emacs
bash_profile
zshrc file
Steps to Set up the environment variable :-
Download the jdk from JAVA
install it by double click
Now set-up environment variables in your file
a. For emacs.profile you can use this link OR see the screenshot below
b. For ZSH profile setup -
1. export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_112.jdk/Contents/Home
2. source ~/.zshrc - Restart zshrc to reflect the changes.
3. echo $JAVA_HOME - make sure path is set up properly
----> /Library/Java/JavaVirtualMachines/jdk1.8.0_112.jdk/Contents/Home
4. java -version
--> java version "1.8.0_112" Java(TM) SE Runtime Environment (build 1.8.0_112-b16)Java HotSpot(TM) 64-Bit Server VM (build 25.112-b16, mixed mode)
All set Now you can easily upgrade or degrade the JAVA version..

Previously I used alias'es in .zshrc for easy switching between versions but today I use SDKMAN.
SDKMAN can also handle setting default java for the system, and downloading and installing new java versions.
Once sdkman is installed you can then do commands similar to what is possible with the nvm tool for handling node versions.
sdk list java will list the java versions available on your system as well as available online for installation including their identifier that you can use in the sdk use, sdk default and sdk install commands.
e.g. to install Amazon Corretto 11.0.8 and ask if it should be the new default do this:
sdk install java 11.0.8-amzn
A feature I also use regularly is the .sdkmanrc file.
If you place that in a directory on your machine and run the sdk env command in the directory then you can configure tool versions used only in that directory. It is also possible to make sdkman switch tool versions automatically using the sdkman_auto_env=true configuration.
sdkman also supports handling other tools for the JVM such as gradle, kotlin, maven and more.
For more information check out https://sdkman.io/usage#env

With no additional tools to install, an easy way to have a separately installed JDK recognized as a first class member by /usr/libexec/java_home -V is to symlink it as follows:
sudo ln -s <path> /Library/Java/JavaVirtualMachines/jdk-[some-identifier].jdk
<path> is expected to be a directory containing subdirectories Contents/Home/bin etc.
A common use case is to register the JDK/JRE included with Android Studio:
The default location for the Java tools in recent versions of Android Studio on macOS is /Applications/Android\ Studio.app/Contents/jre. We will use jdk-android-studio.jdk as the identifier:
sudo ln -s /Applications/Android\ Studio.app/Contents/jre /Library/Java/JavaVirtualMachines/jdk-android-studio.jdk
Now, /usr/libexec/java_home -V will list it under Matching Java Virtual Machines:
$ /usr/libexec/java_home -V
Matching Java Virtual Machines (1):
11.0.13 (arm64) "JetBrains s.r.o." - "OpenJDK 11.0.13" /Applications/Android Studio.app/Contents/jre/Contents/Home
/Applications/Android Studio.app/Contents/jre/Contents/Home

If you are using fish and you are using mac and you want to be able to switch between JDK's, then below works for me on mac.
#kenglxn's answer didn't work for me and I figured out it bcos didn't set -g which is global !
Put below under ~/.config/fish/config.fish
alias j8="jhome -v 1.8.0_162"
alias j9="jhome -v 9.0.1"
function jhome
set -g -x JAVA_HOME (/usr/libexec/java_home $argv)
echo "JAVA_HOME:" $JAVA_HOME
echo "java -version:"
java -version
end
funcsave jhome
To know which version /minor version you have installed, you can do :
/usr/libexec/java_home -V 579ms  Wed 14 Feb 11:44:01 2018
Matching Java Virtual Machines (3):
9.0.1, x86_64: "Java SE 9.0.1" /Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home
1.8.0_162, x86_64: "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home
1.8.0_121, x86_64: "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home

If you have multiple versions and you want to run something by using a specific version, use this example:
/usr/libexec/java_home -v 1.7.0_75 --exec java -jar you-file.jar

Based on #markhellewell answer I created a couple of alias functions that will do it for you. Just add these to your shell startup file
#list available jdks
alias jdks="/usr/libexec/java_home -V"
# jdk version switching - e.g. `jdk 6` will switch to version 1.6
function jdk() {
echo "Switching java version";
export JAVA_HOME=`/usr/libexec/java_home -v 1.$1`;
java -version;
}
https://gist.github.com/Noyabronok/0a90e1f3c52d1aaa941013d3caa8d0e4

Here is how I do it on my Linux (Ubuntu / Mint mate), I guess Mac can do it similarly.
Install & config
Steps:
[Basic - part]
Download jdk (the .tgz file) by hand.
Uncompress & rename properly, at a proper location.
e.g /mnt/star/program/java/jdk-1.8
Make a soft link, which will be changed to switch java version later.
e.g ln -s /mnt/star/program/java/jdk-1.8 /mnt/star/program/java/java
Thus /mnt/star/program/java/java is the soft link.
Set JAVA_HOME in a start script.
Could use file like /etc/profile.d/eric.sh, or just use ~/.bashrc.
e.g JAVA_HOME=/mnt/star/program/java/java
Then open a new bash shell. java -version should print the java version.
[More version - part]
Download & install more Java version, as need, similar as above steps.
e.g
/mnt/star/program/java/jdk-11
[Switch - part]
In ~/.bashrc, define variable for various Java version.
e.g
_E_JAVA_HOME_11='/mnt/star/program/java/jdk-11'
_E_JAVA_HOME_8='/mnt/star/program/java/jdk-8'
# dir of default version,
_E_JAVA_HOME_D=$_E_JAVA_HOME_8
In ~/.bashrc, define command to switch Java version.
e.g
## switch java version,
alias jv11="rm $JAVA_HOME; ln -s $_E_JAVA_HOME_11 $JAVA_HOME"
alias jv8="rm $JAVA_HOME; ln -s $_E_JAVA_HOME_8 $JAVA_HOME"
# default java version,
alias jvd="rm $JAVA_HOME; ln -s $_E_JAVA_HOME_D $JAVA_HOME"
alias jv="java -version"
In terminal, source ~/.bashrc to make the changes take effect.
Then could switch using the defined commands.
Commands - from above config
Commands:
jv11
Switch to Java 11
jv8
Switch to Java 8
jvd
Switch to default Java version, which is denoted by _E_JAVA_HOME_D defined above.
jv
Show java version.
Example output:
eric#eric-pc:~$ jv
java version "1.8.0_191"
Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)
eric#eric-pc:~$ jv11
eric#eric-pc:~$ jv
java version "11.0.1" 2018-10-16 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.1+13-LTS)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.1+13-LTS, mixed mode)
eric#eric-pc:~$ jvd
eric#eric-pc:~$ jv
java version "1.8.0_191"
Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)
eric#eric-pc:~$
Mechanism
It switch by changing the soft link, which is used as JAVA_HOME.
Tips
On my machine when install jdk by hand, I keep the minor version, then make a soft link with the major version but without the minor version.
e.g
// this is the actual dir,
jdk1.8.0_191
// this is a soft link to jdk1.8.0_191
jdk-8
// this is a soft link to jdk-8 or jdk-11
java
I define command alias in ~/.bashrc, but define variable in a separate file.
I am using ~/.eric_var to define the variables, and ~/.bashrc will source it (e.g source $HOME/.eric_var).

add this function to bashrc or zshrc, java-change [version] to choose the JDK
# set and change java versions
function java-change() {
echo "----- old java version -----"
java -version
if [ $# -ne 0 ]; then
export JAVA_HOME=`/usr/libexec/java_home -v $#`
export PATH=$JAVA_HOME/bin:$PATH
fi
echo "----- new java version -----"
java -version
}

CentOS7: Setting default JAVA as Oracle JDK and not openJDK

I have a machine with CentOS7. The default Java is
openjdk version "1.8.0_131"
OpenJDK Runtime Environment (build 1.8.0_131-b12)
OpenJDK 64-Bit Server VM (build 25.131-b12, mixed mode)
I want to change this to
java version "1.8.0_51"
Java(TM) SE Runtime Environment (build 1.8.0_51-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.51-b03, mixed mode)
To do so, I have so far followed the steps as given below.
Download jdk-8u212-linux-x64.tar.gz file
I could not untar the above using tar -zxvf jdk-8u212-linux64.tar.gzto a specified directory. Hence I used 7-zip and the extracted the JDK1.8.0_212 folder and copied the same to /usr/lib/jvm
Then I made the necessary changes at /etc/profile. There I set the JAVA_HOME as export JAVA_HOME=/usr/lib/jvm/jdk1.8.0_212 and followed by export PATH=$PATH:$JAVA_HOME\bin
However, when I typed update-alternatives --config java I could not see jdk1.8.0_212/bin/java as path. Instead I saw only openjdk options.
My question is: How to set my default Java as Oracle Java as mentioned above. The reason I am asking is I have found that sqljdbc4-x.jar is not compatible with openJDK. I have already raised a query here

A simple approach would be to first remove Open JDK using purge then install Oracle jdk..if u are using apt-get it would automatically set the necessary Java Paths.
Here is what I meant.
yum list java*
sudo yum -y remove java*
java -version
cd
mkdir tmp
cd tmp
curl -u uftp:uftp ftp://192.168.2.115/path/developer/jdk-8u151-linux-x64.tar.gz -o jdk-8u151-linux-x64.tar.gz
tar zxvf jdk-8u151-linux-x64.tar.gz
sudo mv jdk1.8.0_151 /usr/share/
sudo vim /etc/profile
#add
export JAVA_HOME=/usr/share/jdk1.8.0_151
export PATH=$JAVA_HOME/bin:$PATH
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
source /etc/profile
java -version
which java
cheers.

Change Java version in a terminal session (Mac OSX) [duplicate]

How can you change the default version of Java on a mac?

First run /usr/libexec/java_home -V which will output something like the following:
Matching Java Virtual Machines (3):
1.8.0_05, x86_64: "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0_05.jdk/Contents/Home
1.6.0_65-b14-462, x86_64: "Java SE 6" /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
1.6.0_65-b14-462, i386: "Java SE 6" /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
/Library/Java/JavaVirtualMachines/jdk1.8.0_05.jdk/Contents/Home
Pick the version you want to be the default (1.6.0_65-b14-462 for arguments sake) then:
export JAVA_HOME=`/usr/libexec/java_home -v 1.6.0_65-b14-462`
or you can specify just the major version, like:
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`
Now when you run java -version you will see:
java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-462-11M4609)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-462, mixed mode)
Add the export JAVA_HOME… line to your shell’s init file.
For Bash (as stated by antonyh):
export JAVA_HOME=$(/usr/libexec/java_home -v 1.8)
For Fish (as stated by ormurin)
set -x JAVA_HOME (/usr/libexec/java_home -d64 -v1.8)
Updating the .zshrc file should work:
nano ~/.zshrc
export JAVA_HOME=$(/usr/libexec/java_home -v 1.8.0)
Press CTRL+X to exit the editor
Press Y to save your changes
source ~/.zshrc
echo $JAVA_HOME
java -version

Adding to the above answers, I put the following lines in my .bash_profile (or .zshrc for MacOS 10.15+) which makes it really convenient to switch (including #elektromin's comment for java 9):
alias j12="export JAVA_HOME=`/usr/libexec/java_home -v 12`; java -version"
alias j11="export JAVA_HOME=`/usr/libexec/java_home -v 11`; java -version"
alias j10="export JAVA_HOME=`/usr/libexec/java_home -v 10`; java -version"
alias j9="export JAVA_HOME=`/usr/libexec/java_home -v 9`; java -version"
alias j8="export JAVA_HOME=`/usr/libexec/java_home -v 1.8`; java -version"
alias j7="export JAVA_HOME=`/usr/libexec/java_home -v 1.7`; java -version"
After inserting, execute $ source .bash_profile
I can switch to Java 8 by typing the following:
$ j8
java version "1.8.0_102"
Java(TM) SE Runtime Environment (build 1.8.0_102-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.102-b14, mixed mode)

A small fish function based on /usr/libexec/java_home
function jhome
set JAVA_HOME (/usr/libexec/java_home $argv)
echo "JAVA_HOME:" $JAVA_HOME
echo "java -version:"
java -version
end
If you don't use fish, you can do something similar in bash:
#!/bin/bash
jhome () {
export JAVA_HOME=`/usr/libexec/java_home $#`
echo "JAVA_HOME:" $JAVA_HOME
echo "java -version:"
java -version
}
Then to switch between javas do:
$> jhome #switches to latest java
$> jhome -v 1.7 #switches to java 1.7
$> jhome -v 1.6 #switches to java 1.6
ref: https://gist.github.com/kenglxn/1843d552dff4d4233271

Use jenv is an easy way. (Update 2022)
Install jenv: see Getting started
Install java with brew
brew install openjdk#11
ln -s /usr/local/opt/openjdk#11/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk-11.jdk
#other java
brew install openjdk#8
brew install openjdk#17
Add java to jenv
jenv add /Library/Java/JavaVirtualMachines/openjdk-11.jdk/Contents/Home
Use: refer to jenv

It is a little bit tricky, but try to follow the steps described in Installing Java on OS X 10.9 (Mavericks). Basically, you gonna have to update your alias to java.
Step by step:
After installing JDK 1.7, you will need to do the sudo ln -snf in order to change the link to current java. To do so, open Terminal and issue the command:
sudo ln -nsf /Library/Java/JavaVirtualMachines/jdk1.7.0_51.jdk/Contents \
/System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK
Note that the directory jdk1.7.0_51.jdk may change depending on the SDK version you have installed.
Now, you need to set JAVA_HOME to point to where jdk_1.7.0_xx.jdk was installed. Open again the Terminal and type:
export JAVA_HOME="/Library/Java/JavaVirtualMachines/jdk1.7.0_51.jdk/Contents/Home"
You can add the export JAVA_HOME line above in your .bashrc file to have java permanently in your Terminal

install JDK, not just JRE
/usr/libexec/java_home -v 1.8
gives
/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home
next
touch .bash_profile
open -a TextEdit.app .bash_profile
TextEdit will show you a blank page which you can fill in.
add to doc:
export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home
in terminal:
export JAVA_HOME="$(/usr/libexec/java_home -v 1.8)"
try the command:
javac -version
should output:
javac 1.8.0_111

tl;dr
Add the line:
export JAVA_HOME='/Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home'
to the file
~/.bash_profile
(replace jdk1.8.0_144.jdk with your downloaded version)
then source ~/.bash_profile

Use jenv, it is like a Java environment manager. It is super easy to use and clean
For Mac, follow the steps:
brew install jenv
git clone https://github.com/gcuisinier/jenv.git ~/.jenv
Installation: If you are using bash follow these steps:
$ echo 'export PATH="$HOME/.jenv/bin:$PATH"' >> ~/.bash_profile
echo 'eval "$(jenv init -)"' >> ~/.bash_profile
$ exec $SHELL -l
Add desired versions of JVM to jenv:
jenv add /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
jenv add /System/Library/Java/JavaVirtualMachines/1.8.0.jdk/Contents/Home
Check the installed versions:
jenv versions
Set the Java version you want to use by:
jenv global oracle64-1.6.0

Four easy steps using terminal for people who uses the default process.. :)
echo $JAVA_HOME gives you current java home. For eg: /Library/Java/JavaVirtualMachines/jdk1.8.0_191.jdk/Contents/Home/
cd /Library/Java/JavaVirtualMachines/ will take you to the folder where u normally install jdks (It might be different for your machines)
ls shows you available folders (normally it will have the version numbers, for eg: jdk1.8.0_191.jdk openjdk-11.0.2.jdk)
export JAVA_HOME='/Library/Java/JavaVirtualMachines/openjdk-11.0.2.jdk/Contents/Home' will change the java home..

Consider the following approach only to change the JDK for each and specific tab of your terminal (i.e: iTerm).
Having in the /Library/Java/JavaVirtualMachines path the two following jdks
openjdk8u275-b01
openjdk-11.0.9.1+1
And in the .bash_profile file the following:
export JAVA_HOME=/Library/Java/JavaVirtualMachines/openjdk-11.0.9.1+1/Contents/Home
export PATH=$JAVA_HOME/bin:$PATH
If you open Iterm - with the first Tab A - and the following commands are executed:
javac -version
javac 11.0.9.1
java -version
openjdk version "11.0.9.1" 2020-11-04
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.9.1+1)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.9.1+1, mixed mode)
The output is correct and expected
But if you open a second Tab B and you need override the default JDK then write in the terminal the following:
export JAVA_HOME=/Library/Java/JavaVirtualMachines/openjdk8u275-b01/Contents/Home/
export PATH=$JAVA_HOME/bin:$PATH
Then
javac -version
javac 1.8.0_275
java -version
openjdk version "1.8.0_275"
OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_275-b01)
OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.275-b01, mixed mode)
It works fine. Of course if the Tab B is closed or you open a new Tab C all work according the .bash_profile settings (therefore the default settings)

macOS El Capitan or newer will choose the higher version of the JDK available in /Library/Java/JavaVirtualMachines, so in order to downgrade you may rename the file Info.plist to something else like Info.plist.disabled so that the OS will choose a previous version.

function setjdk() {
if [ $# -ne 0 ]; then
removeFromPath '/System/Library/Frameworks/JavaVM.framework/Home/bin'
if [ -n "${JAVA_HOME+x}" ]; then
removeFromPath $JAVA_HOME
fi
export JAVA_HOME=`/usr/libexec/java_home -v $#`
export PATH=$JAVA_HOME/bin:$PATH
fi
}
put this in your ~/.profile and use it in your terminal like so setjdk 1.8, setjdk 1.7, setjdk 9 etc etc...
If you don't have removeFromPath then it is:
function removeFromPath() {
export PATH=$(echo $PATH | sed -E -e "s;:$1;;" -e "s;$1:?;;")
}

You can add it to your .bash_profile to have the version set by default.
//Open bash profile
open ~/.bash_profile
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`
// run bash profile
source ~/.bash_profile

add following command to the ~/.zshenv file
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`

Add following in your ~/.bash_profile and set the default java version accordingly.
export JAVA_8_HOME=$(/usr/libexec/java_home -v1.8)
export JAVA_11_HOME=$(/usr/libexec/java_home -v11)
alias java8='export JAVA_HOME=$JAVA_8_HOME'
alias java11='export JAVA_HOME=$JAVA_11_HOME'
# default to Java 8
java8
I am using macOS and have installed java using brew.
Edit:
If you are not using bash please update the correct shell file, example, if you are using zsh then it will be ~/.zshrc

Add the following line of code to your .zshrc (or bash_profile):
alias j='f(){ export JAVA_HOME=/usr/libexec/java_home -v $1 };f'
Save to session:
$ source .zshrc
Run command (e.g. j 13, j14, j1.8...)
$ j 1.8
Explanation
This is parameterised so you do not need to update the script like other solutions posted. If you do not have the JVM installed you are told. Sample cases below:
/Users/user/IDE/project $ j 1.8
/Users/user/IDE/project $ java -version
openjdk version "1.8.0_265"
OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_265-b01)
OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.265-b01, mixed mode)
/Users/user/IDE/project $ j 13
/Users/user/IDE/project $ java -version
openjdk version "13.0.2" 2020-01-14
OpenJDK Runtime Environment (build 13.0.2+8)
OpenJDK 64-Bit Server VM (build 13.0.2+8, mixed mode, sharing)
/Users/user/IDE/project $ j 1.7
Unable to find any JVMs matching version "1.7".

Check Java version: java -version
Switch between versions: https://devqa.io/brew-install-java/
open ~/.bash_profile
export JAVA_8_HOME=$(/usr/libexec/java_home -v1.8)
export JAVA_11_HOME=$(/usr/libexec/java_home -v11)
alias java8='export JAVA_HOME=$JAVA_8_HOME'
alias java11='export JAVA_HOME=$JAVA_11_HOME'
source ~/.bash_profile
When we are switching to java11 or java8, java -version command is not showing the correct version.
In that case use mvn -version to see the correct java version is used for building the solution

From the Apple's official java_home(1) man page:
**USAGE**
/usr/libexec/java_home helps users set a $JAVA_HOME in their login rc files, or provides a way for
command-line Java tools to use the most appropriate JVM which can satisfy a minimum version or archi-
tecture requirement. The --exec argument can invoke tools in the selected $JAVA_HOME/bin directory,
which is useful for starting Java command-line tools from launchd plists without hardcoding the full
path to the Java command-line tool.
Usage for bash-style shells:
$ export JAVA_HOME=`/usr/libexec/java_home`
Usage for csh-style shells:
% setenv JAVA_HOME `/usr/libexec/java_home`

JDK Switch Script
I have adapted the answer from #Alex above and wrote the following to fix the code for Java 9.
$ cat ~/.jdk
#!/bin/bash
#list available jdks
alias jdks="/usr/libexec/java_home -V"
# jdk version switching - e.g. `jdk 6` will switch to version 1.6
function jdk() {
echo "Switching java version $1";
requestedVersion=$1
oldStyleVersion=8
# Set the version
if [ $requestedVersion -gt $oldStyleVersion ]; then
export JAVA_HOME=$(/usr/libexec/java_home -v $1);
else
export JAVA_HOME=`/usr/libexec/java_home -v 1.$1`;
fi
echo "Setting JAVA_HOME=$JAVA_HOME"
which java
java -version;
}
Switch to Java 8
$ jdk 8
Switching java version 8
Setting JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home
/usr/bin/java
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)
Switch to Java 9
$ jdk 9
Switching java version 9
Setting JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home
/usr/bin/java
java version "9.0.1"
Java(TM) SE Runtime Environment (build 9.0.1+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)

If still u are not able to set it. using this command.
export JAVA_HOME=/usr/libexec/java_home -v 1.8
then you have to use this one.
export JAVA_HOME=$(/usr/libexec/java_home -v 1.8)
it will surely work.

First find out where do you store the environment variables-
emacs
bash_profile
zshrc file
Steps to Set up the environment variable :-
Download the jdk from JAVA
install it by double click
Now set-up environment variables in your file
a. For emacs.profile you can use this link OR see the screenshot below
b. For ZSH profile setup -
1. export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_112.jdk/Contents/Home
2. source ~/.zshrc - Restart zshrc to reflect the changes.
3. echo $JAVA_HOME - make sure path is set up properly
----> /Library/Java/JavaVirtualMachines/jdk1.8.0_112.jdk/Contents/Home
4. java -version
--> java version "1.8.0_112" Java(TM) SE Runtime Environment (build 1.8.0_112-b16)Java HotSpot(TM) 64-Bit Server VM (build 25.112-b16, mixed mode)
All set Now you can easily upgrade or degrade the JAVA version..

Previously I used alias'es in .zshrc for easy switching between versions but today I use SDKMAN.
SDKMAN can also handle setting default java for the system, and downloading and installing new java versions.
Once sdkman is installed you can then do commands similar to what is possible with the nvm tool for handling node versions.
sdk list java will list the java versions available on your system as well as available online for installation including their identifier that you can use in the sdk use, sdk default and sdk install commands.
e.g. to install Amazon Corretto 11.0.8 and ask if it should be the new default do this:
sdk install java 11.0.8-amzn
A feature I also use regularly is the .sdkmanrc file.
If you place that in a directory on your machine and run the sdk env command in the directory then you can configure tool versions used only in that directory. It is also possible to make sdkman switch tool versions automatically using the sdkman_auto_env=true configuration.
sdkman also supports handling other tools for the JVM such as gradle, kotlin, maven and more.
For more information check out https://sdkman.io/usage#env

With no additional tools to install, an easy way to have a separately installed JDK recognized as a first class member by /usr/libexec/java_home -V is to symlink it as follows:
sudo ln -s <path> /Library/Java/JavaVirtualMachines/jdk-[some-identifier].jdk
<path> is expected to be a directory containing subdirectories Contents/Home/bin etc.
A common use case is to register the JDK/JRE included with Android Studio:
The default location for the Java tools in recent versions of Android Studio on macOS is /Applications/Android\ Studio.app/Contents/jre. We will use jdk-android-studio.jdk as the identifier:
sudo ln -s /Applications/Android\ Studio.app/Contents/jre /Library/Java/JavaVirtualMachines/jdk-android-studio.jdk
Now, /usr/libexec/java_home -V will list it under Matching Java Virtual Machines:
$ /usr/libexec/java_home -V
Matching Java Virtual Machines (1):
11.0.13 (arm64) "JetBrains s.r.o." - "OpenJDK 11.0.13" /Applications/Android Studio.app/Contents/jre/Contents/Home
/Applications/Android Studio.app/Contents/jre/Contents/Home

If you are using fish and you are using mac and you want to be able to switch between JDK's, then below works for me on mac.
#kenglxn's answer didn't work for me and I figured out it bcos didn't set -g which is global !
Put below under ~/.config/fish/config.fish
alias j8="jhome -v 1.8.0_162"
alias j9="jhome -v 9.0.1"
function jhome
set -g -x JAVA_HOME (/usr/libexec/java_home $argv)
echo "JAVA_HOME:" $JAVA_HOME
echo "java -version:"
java -version
end
funcsave jhome
To know which version /minor version you have installed, you can do :
/usr/libexec/java_home -V 579ms  Wed 14 Feb 11:44:01 2018
Matching Java Virtual Machines (3):
9.0.1, x86_64: "Java SE 9.0.1" /Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home
1.8.0_162, x86_64: "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home
1.8.0_121, x86_64: "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home

If you have multiple versions and you want to run something by using a specific version, use this example:
/usr/libexec/java_home -v 1.7.0_75 --exec java -jar you-file.jar

Based on #markhellewell answer I created a couple of alias functions that will do it for you. Just add these to your shell startup file
#list available jdks
alias jdks="/usr/libexec/java_home -V"
# jdk version switching - e.g. `jdk 6` will switch to version 1.6
function jdk() {
echo "Switching java version";
export JAVA_HOME=`/usr/libexec/java_home -v 1.$1`;
java -version;
}
https://gist.github.com/Noyabronok/0a90e1f3c52d1aaa941013d3caa8d0e4

Here is how I do it on my Linux (Ubuntu / Mint mate), I guess Mac can do it similarly.
Install & config
Steps:
[Basic - part]
Download jdk (the .tgz file) by hand.
Uncompress & rename properly, at a proper location.
e.g /mnt/star/program/java/jdk-1.8
Make a soft link, which will be changed to switch java version later.
e.g ln -s /mnt/star/program/java/jdk-1.8 /mnt/star/program/java/java
Thus /mnt/star/program/java/java is the soft link.
Set JAVA_HOME in a start script.
Could use file like /etc/profile.d/eric.sh, or just use ~/.bashrc.
e.g JAVA_HOME=/mnt/star/program/java/java
Then open a new bash shell. java -version should print the java version.
[More version - part]
Download & install more Java version, as need, similar as above steps.
e.g
/mnt/star/program/java/jdk-11
[Switch - part]
In ~/.bashrc, define variable for various Java version.
e.g
_E_JAVA_HOME_11='/mnt/star/program/java/jdk-11'
_E_JAVA_HOME_8='/mnt/star/program/java/jdk-8'
# dir of default version,
_E_JAVA_HOME_D=$_E_JAVA_HOME_8
In ~/.bashrc, define command to switch Java version.
e.g
## switch java version,
alias jv11="rm $JAVA_HOME; ln -s $_E_JAVA_HOME_11 $JAVA_HOME"
alias jv8="rm $JAVA_HOME; ln -s $_E_JAVA_HOME_8 $JAVA_HOME"
# default java version,
alias jvd="rm $JAVA_HOME; ln -s $_E_JAVA_HOME_D $JAVA_HOME"
alias jv="java -version"
In terminal, source ~/.bashrc to make the changes take effect.
Then could switch using the defined commands.
Commands - from above config
Commands:
jv11
Switch to Java 11
jv8
Switch to Java 8
jvd
Switch to default Java version, which is denoted by _E_JAVA_HOME_D defined above.
jv
Show java version.
Example output:
eric#eric-pc:~$ jv
java version "1.8.0_191"
Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)
eric#eric-pc:~$ jv11
eric#eric-pc:~$ jv
java version "11.0.1" 2018-10-16 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.1+13-LTS)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.1+13-LTS, mixed mode)
eric#eric-pc:~$ jvd
eric#eric-pc:~$ jv
java version "1.8.0_191"
Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)
eric#eric-pc:~$
Mechanism
It switch by changing the soft link, which is used as JAVA_HOME.
Tips
On my machine when install jdk by hand, I keep the minor version, then make a soft link with the major version but without the minor version.
e.g
// this is the actual dir,
jdk1.8.0_191
// this is a soft link to jdk1.8.0_191
jdk-8
// this is a soft link to jdk-8 or jdk-11
java
I define command alias in ~/.bashrc, but define variable in a separate file.
I am using ~/.eric_var to define the variables, and ~/.bashrc will source it (e.g source $HOME/.eric_var).

add this function to bashrc or zshrc, java-change [version] to choose the JDK
# set and change java versions
function java-change() {
echo "----- old java version -----"
java -version
if [ $# -ne 0 ]; then
export JAVA_HOME=`/usr/libexec/java_home -v $#`
export PATH=$JAVA_HOME/bin:$PATH
fi
echo "----- new java version -----"
java -version
}

Install latest java version in ubuntu 16.04 [duplicate]

How do I install Java Development Kit (JDK) 10 on Ubuntu?
The installation instructions on Oracle's help center only explain how to download and extract the archive on Linux platform, without any system setup.

Update: JDK 11 Now Available
sudo apt-get install openjdk-11-jdk
For JDK 10
Option 1: Easy Installation (PPA)
sudo add-apt-repository ppa:linuxuprising/java
sudo apt-get update
sudo apt-get install oracle-java10-installer
Then set as default with:
sudo apt-get install oracle-java10-set-default
And finally verify Installation with:
$ java -version
java version "10.0.1" 2018-04-17
Java(TM) SE Runtime Environment 18.3 (build 10.0.1+10)
Java HotSpot(TM) 64-Bit Server VM 18.3 (build 10.0.1+10, mixed mode)
Source: Linux Uprising
Option 2: Manual Installation
Download OpenJDK 10 binaries for Linux.
Untar the downloaded archive:
tar xzvf openjdk-10_linux-x64_bin.tar.gz
Move the extracted archive to where your system keeps your installed JDKs:
sudo mv jdk-10 /usr/lib/jvm/java-10-openjdk-amd64/
Add the new Java alternative:
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-10-openjdk-amd64/bin/java 1
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/java-10-openjdk-amd64/bin/javac 1
Update your system's java alternatives and choose JDK 10:
$ sudo update-alternatives --config java
here are 3 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
0 /usr/lib/jvm/java-9-openjdk-amd64/bin/java 1091 auto mode
* 1 /usr/lib/jvm/java-10-openjdk-amd64/bin/java 1 manual mode
2 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 manual mode
3 /usr/lib/jvm/java-9-openjdk-amd64/bin/java 1091 manual mode
Press <enter> to keep the current choice[*], or type selection number:
and
$ sudo update-alternatives --config javac
There are 3 choices for the alternative javac (providing /usr/bin/javac).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-9-openjdk-amd64/bin/javac 1091 auto mode
1 /usr/lib/jvm/java-10-openjdk-amd64/bin/javac 1 manual mode
2 /usr/lib/jvm/java-8-openjdk-amd64/bin/javac 1081 manual mode
3 /usr/lib/jvm/java-9-openjdk-amd64/bin/javac 1091 manual mode
Press <enter> to keep the current choice[*], or type selection number: 1
update-alternatives: using /usr/lib/jvm/java-10-openjdk-amd64/bin/javac to provide /usr/bin/javac (javac) in manual mode
Verify your installation with:
$ java --version
openjdk 10 2018-03-20
OpenJDK Runtime Environment 18.3 (build 10+46)
OpenJDK 64-Bit Server VM 18.3 (build 10+46, mixed mode)
and
$ javac --version
javac 10
Done
If you prefer Oracle's JDK, download it and follow the installation steps as shown above.

I've found SdkMan! a very useful tool because it provides a convenient way for managing your JDKs from the shell.
For example, once it is installed, you can:
Install a specific JDK version: sdk install java 10.0.2-open
Downloading: java 10.0.2-open
In progress...
################# 12,3%
Use a specific JDK version: sdk use java 10.0.2-open
Using java version 10.0.2-open in this shell.
List available JDK: sdk list java
===================================================================
Available Java Versions
===================================================================
9.0.4-open
+ 8u161-oracle
8.0.191-oracle
> + 8.0.171-oracle
7.0.191-zulu
12.ea.15-open
11.0.1-open
10.0.2-open
1.0.0-rc8-graal
===================================================================
+ - local version
* - installed
> - currently in use
=======================================================================
And much more
See https://sdkman.io/usage

There is a ppa on java 10 that installs oracle's java: https://launchpad.net/~linuxuprising/+archive/ubuntu/java
I am not sure if this will be maintained though.
It seems to be a copy of the webupd8 way on how to handle oracle java installation (ref: documentation).
How to use this ppa:
sudo add-apt-repository ppa:linuxuprising/java
sudo apt-get update
sudo apt-get install oracle-java10-installer
Verify installation:
$ /usr/lib/jvm/java-10-oracle/bin/java -version
java version "10.0.1" 2018-04-17
Java(TM) SE Runtime Environment 18.3 (build 10.0.1+10)
Java HotSpot(TM) 64-Bit Server VM 18.3 (build 10.0.1+10, mixed mode)
Setting up environment variables (make java10 default)
sudo apt-get install oracle-java10-set-default

Note: You need update-alternatives only if you have multiple java versions.
Note: You can purge everything about Java before fresh installing new Java.
sudo apt purge java*
For Java 10 fresh installation
Download JDK 10 from here (you can download JRE and server JRE): http://www.oracle.com/technetwork/java/javase/downloads/index.html
Extract and put somewhere in /opt/java directory. You putting JDK in /opt/java directory makes it will be usable for all users as it is being in the public /opt directory.
(Note: I downloaded JDK, JRE, and server JRE, and extracted JDK and renamed extracted the folder to jdk10, extracted JRE and renamed extracted the folder to jre10, and extracted server JRE and renamed extracted the folder to jre10server as shown in below snapshot).
Update your /etc/environment file as below
Now, you need to reload the /etc/environment script file into the system using source command as below.
source /etc/environment
If you want to know more about update-alternatives then here is the link: https://askubuntu.com/questions/159575/how-do-i-make-java-default-to-a-manually-installed-jre-jdk

You need to do update-alternatives --install before the final step.
sudo update-alternatives --install "/usr/bin/java" java "/usr/lib/jvm/java-10-openjdk-amd64/bin/java" 1
sudo update-alternatives --install "/usr/bin/javac" javac "/usr/lib/jvm/java-10-openjdk-amd64/bin/javac" 1

I've found a repo
sudo add-apt-repository ppa:openjdk-r/ppa
sudo apt update
sudo apt install openjdk-10-jdk
Repo home page

Install Jdk 10 On Linux Ubuntu
Download the required tarball from from Oracle official
website, i.e.
https://www.oracle.com
Unzip this tarball using "tar -zxvf tarball_name”
Create a folder named "java" in "/usr/lib", you need root permission
sudo mkdir /usr/lib/java
Move the extracted folder to “/usr/lib/java/” by using the following command:
sudo mv java-10-dir-name/ /usr/lib/java/
Now go to the location, i.e. cd /usr/lib/java/java-10-dir-name/
Next, run these below scripts in terminal:
sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/java/java-10-dir-name/bin/java" 1
sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/java/java-10-dir-name/bin/javac" 1
sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/java/java-10-dir-name/bin/javaws" 1
NOTE: In the commands given above, you have to name the extracted directory of "java" instead of "java-10-dir-name".
Update the JAVA_HOME in your ~/.bashrc
export JAVA_HOME=/usr/lib/java/java-10-dir-name
set PATH="$PATH:$JAVA_HOME/bin"
export PATH
Verify the installation
verify whether Java 10 is installed correctly in your machine, execute the following command in your terminal:
$ java --version
openjdk 10 2018-03-20
OpenJDK Runtime Environment 18.3 (build 10+46)
OpenJDK 64-Bit Server VM 18.3 (build 10+46, mixed mode)
And
$ javac --version
javac 10

Changing java 7 to java 8 ubuntu openjdk not working

I have a project that runs on Jenkins using docker. At start the docker have java 7 installed by default which is necesary for the project to build. But after, the proyect build and is up, I need to install java 8 to run the e2e tests, selenium server needs java 8. So to install java 8 i use openjdk8 the following ways:
apt-get -y update
apt-get install -y openjdk-8-jdk
echo 'Changing Java version, it should be 8'
export JAVA_HOME="/usr/lib/jvm/java-8-openjdk-amd64"
echo "path"
echo $JAVA_HOME
echo "version java"
java -version
The problem is that when this runs it still outputs the java 7. Below output from the code above.
Changing Java version, it should be 8
path
/usr/lib/jvm/java-8-openjdk-amd64
version java
java version "1.7.0_80"
Java(TM) SE Runtime Environment (build 1.7.0_80-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.80-b11, mixed mode)
Any idea what could be happening?

you can do following:
update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-8-openjdk-amd64/bin/java 1
update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/java-8-openjdk-amd64/bin/javac 1
and then by using following you can set the config to use which version:
update-alternative --config java
update-alternative --config javac

Make sure that java8 home/bin is first in the path
update-java-alternatives --list | grep java-8
export JAVA_HOME= java 8 path here
export PATH=$JAVE_HOME/bin:$PATH

Develop Reference

Java is a programming language and computing platform first released by Sun Microsystems in 1995.