Setup environment (SDKMAN)

SDKMAN is a command line tool that allows us to install different versions of Java, Gradle, Maven and more. SDKMAN also takes care of setting environment variables for you. Installing SDKMAN.

Install

$ curl -s "https://get.sdkman.io" | bash
$ source "~/.sdkman/bin/sdkman-init.sh"

Check version after installation
```
$ sdk version
SDKMAN 5.7.4+362
```

List all available Java versions

$ sdk list java

This will print all versions available to SDKMAN from different vendors.

================================================================================
Available Java Versions
================================================================================
 Vendor        | Use | Version      | Dist    | Status     | Identifier
--------------------------------------------------------------------------------
 AdoptOpenJDK  |     | 14.0.1.j9    | adpt    |            | 14.0.1.j9-adpt
               |     | 14.0.1.hs    | adpt    | installed  | 14.0.1.hs-adpt
               |     | 13.0.2.j9    | adpt    |            | 13.0.2.j9-adpt
               |     | 13.0.2.hs    | adpt    |            | 13.0.2.hs-adpt
               |     | 12.0.2.j9    | adpt    |            | 12.0.2.j9-adpt
               |     | 12.0.2.hs    | adpt    |            | 12.0.2.hs-adpt
               |     | 11.0.7.j9    | adpt    |            | 11.0.7.j9-adpt
               |     | 11.0.7.hs    | adpt    |            | 11.0.7.hs-adpt
               |     | 11.0.6.hs    | adpt    | local only | 11.0.6.hs-adpt
               |     | 8.0.252.j9   | adpt    |            | 8.0.252.j9-adpt
               | >>> | 8.0.252.hs   | adpt    | installed  | 8.0.252.hs-adpt
...

The above shows three versions of Java installed

14.0.1.hs-adpt
11.0.6.hs-adpt
8.0.252.hs-adpt

The version 11.0.6.hs-adpt is not available anymore as there is a newer version available, the version 11.0.7.hs-adpt. That’s why it has the status of local only.

The version 8.0.252.hs-adpt is the current default version of Java.

Install the latest Java 11 and Java 14
```
$ sdk install java 14.0.1.hs-adpt
$ sdk install java 11.0.7.hs-adpt
```
OpenJDK comes in two flavours:
1. HotSpot (...x.hs-adpt) is the VM from the OpenJDK community. It is the most widely used VM today and is used in Oracle’s JDK (reference).
2. Eclipse OpenJ9 (...x.j9-adpt) is the VM from the Eclipse community. It is an enterprise-grade VM designed for low memory footprint and fast start-up and is used in IBM’s JDK (reference).

Change the default Java

$ sdk default java 14.0.1.hs-adpt
Default java version set to 14.0.1.hs-adpt

Verify the version

$ java -version
openjdk version "14.0.1" 2020-04-14
OpenJDK Runtime Environment AdoptOpenJDK (build 14.0.1+7)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 14.0.1+7, mixed mode, sharing)

Optionally, add an alias to simplify switching from one version to another.

$ vi ~/.oh-my-zsh/custom/dev.zsh

Add the aliases

alias java11='sdk default java 11.0.7.hs-adpt'
alias java14='sdk default java 14.0.1.hs-adpt'

Note that the aliases will need to be updated when different versions of Java are added or removed.

To switch between versions just use java11 and java14.

$ java14
Default java version set to 14.0.1.hs-adpt

Set the JAVA_HOME environment variable

$ echo $JAVA_HOME
~/.sdkman/candidates/java/current

If the environment variable is missing, it will be blank. Edit the ~/.zshrc to set the JAVA_HOME environment variable.

$ vi ~/.zshrc

Add the JAVA_HOME environment variable

export JAVA_HOME="~/.sdkman/candidates/java/current"

Open a new terminal and verify that this was properly set.

$ ${JAVA_HOME}/bin/java -version
openjdk version "14.0.1" 2020-04-14
OpenJDK Runtime Environment AdoptOpenJDK (build 14.0.1+7)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 14.0.1+7, mixed mode, sharing)

For more details, please refer to: https://sdkman.io/install