# Installing different versions of open jdk through Homebrew(assuming already installed) and already having Java 8.

We need to install a tool called **jenv** - Java version manager which is similar to **nvm**(nodeJs version manager).

```
brew install jenv
```

Export the jenv path to .bash_profile or .zshrc - whatever you are using. I am using .zshrc

```
echo 'export PATH="$HOME/.jenv/bin:$PATH"' >> ~/.zshrc
echo 'eval "$(jenv init -)"' >> ~/.zshrc
```

After executing above command make sure you are having the below in ~/.zshrc

```
export PATH="$HOME/.jenv/bin:$PATH"
eval "$(jenv init -)"
```

Then update the terminal using

```
source ~/.zshrc
```

Check the jenv health
```
jenv doctor
```

It will return something similar to this 

```
[OK]	No JAVA_HOME set
[ERROR]	Java binary in path is not in the jenv shims.
[ERROR]	Please check your path, or try using /path/to/java/home is not a valid path to java installation.
	PATH : /usr/local/Cellar/jenv/0.5.2/libexec/libexec:/Users/gramcha/.jenv/shims:/Users/gramcha/.jenv/shims:/Users/gramcha/.jenv/bin:/Users/gramcha/.jenv/bin:/Users/gramcha/chromedriver:/opt/local/bin:/opt/local/sbin:/Users/gramcha/.jenv/shims:/Users/gramcha/.jenv/bin:/Users/gramcha/.jenv/bin:/Users/gramcha/chromedriver:/opt/local/bin:/opt/local/sbin:/Users/gramcha/.jenv/shims:/Users/gramcha/.jenv/bin:/Users/gramcha/.jenv/shims:/Users/gramcha/.jenv/bin:/Users/gramcha/chromedriver:/opt/local/bin:/opt/local/sbin:/Users/gramcha/.nvm/versions/node/v10.17.0/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
[OK]	Jenv is correctly loaded
```

No need to worry about error message as long as **Jenv is correctly loaded** is printed.

To ensure that JAVA_HOME is correct

```
jenv enable-plugin export
```

Assuming Maven is used and to educate maven about Java version used

```
jenv enable-plugin maven
```

Intalling latest open jdk version(15) at the time of writing this script

```
brew install openjdk
```
It will printout 
```
Updating Homebrew...
==> Downloading https://homebrew.bintray.com/bottles/openjdk-15.0.1.mojave.bottle.tar.gz
==> Downloading from https://d29vzk4ow07wi7.cloudfront.net/a4f00dc8b4c69bff53828f32c82b0a6be41b23a69a7775a95cdbc9e01d9bdb68?response-content-disposition=attachment%3Bfilename%3D%22openjdk-15.0.1.mojave.bottle.tar.gz%22&Policy=eyJTdGF0ZW
######################################################################## 100.0%
==> Pouring openjdk-15.0.1.mojave.bottle.tar.gz
==> Caveats
For the system Java wrappers to find this JDK, symlink it with
  sudo ln -sfn /usr/local/opt/openjdk/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk.jdk

openjdk is keg-only, which means it was not symlinked into /usr/local,
because it shadows the macOS `java` wrapper.

If you need to have openjdk first in your PATH run:
  echo 'export PATH="/usr/local/opt/openjdk/bin:$PATH"' >> ~/.zshrc

For compilers to find openjdk you may need to set:
  export CPPFLAGS="-I/usr/local/opt/openjdk/include"

==> Summary
🍺  /usr/local/Cellar/openjdk/15.0.1: 614 files, 323.8MB
```

Execute the caveats suggested by above install

```
sudo ln -sfn /usr/local/opt/openjdk/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk.jdk
echo 'export PATH="/usr/local/opt/openjdk/bin:$PATH"' >> ~/.zshrc
export CPPFLAGS="-I/usr/local/opt/openjdk/include"
```

similarly if you want to install java8 execute below and follow the caveats.
```
brew install openjdk@8
```

I already having AdoptOpenJDK 8 in my machine. In case if you want to install that 

```
brew install AdoptOpenJDK/openjdk/adoptopenjdk{8,11}
```

Execute below command to see available JVM's in machine

```
/usr/libexec/java_home -V
```

It will print something like this

```
Matching Java Virtual Machines (2):
    15.0.1, x86_64:	"OpenJDK 15.0.1"	/Library/Java/JavaVirtualMachines/openjdk.jdk/Contents/Home
    1.8.0_212, x86_64:	"AdoptOpenJDK 8"	/Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home

/Library/Java/JavaVirtualMachines/openjdk.jdk/Contents/Home

```

Add java 15 and java 8 paths to jenv by copying path from above previous command output.

```
jenv add /Library/Java/JavaVirtualMachines/openjdk.jdk/Contents/Home
jenv add /Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home
```

It will print the below outputs respectively.

```
openjdk64-15.0.1 added
15.0.1 added
15.0 added


openjdk64-1.8.0.212 added
1.8.0.212 added
1.8 added
```

Check the jenv for available versions
```
jenv versions
```

It will print below outputs
```
* system (set by /Users/gramcha/.jenv/version)
  1.8
  1.8.0.212
  15.0
  15.0.1
  openjdk64-1.8.0.212
  openjdk64-15.0.1
```

Set system level version

```
jenv global 15.0
```

and check the java version 

```
java -version
```

and it should print 15.0

```
openjdk version "15.0.1" 2020-10-20
OpenJDK Runtime Environment (build 15.0.1+9)
OpenJDK 64-Bit Server VM (build 15.0.1+9, mixed mode, sharing)
```

Some of projects wants older version like java8 to support that add project wise version.
Go inside the specific project folder and execute below command

```
jenv local 1.8
```

This will create the .java-version file that describes which java version to use.

To set the java specific version at teminal level execute that

```
jenv shell 1.8
```

Check the `jenv versions` it should print
 
```
system
* 1.8 (set by JENV_VERSION environment variable)
  1.8.0.212
  15.0
  15.0.1
  openjdk64-1.8.0.212
  openjdk64-15.0.1
```