SDKMAN, Java9, Jshell, REPL
Working with multiple versions
Most of the times we as developers are working on multiple version of the language or the framework. If not managed properly it can be a nightmare dealing with different projects which use different versions of the same language. Say, project A uses python2 and project B uses python3. In python we have virtual environments which can be managed using, among many others, pipenv. Likewise for Ruby we have rbenv.
There are quite a few languages that run on JVM(Java Virtual Machine). Java, Groovy, Scala being the most prominent ones. SDKMAN! is a tool that facilitates maintaining different versions of JVM based languages.
Installing SDKMAN
curl -s "https://get.sdkman.io" | bash
source "$HOME/.sdkman/bin/sdkman-init.sh" #activating initialization shell script
After Installation we can see the list of all the supported languages and versions using:
sdk list
Likewise to view versions of a particular sdk we can use:
sdk list java
Replace java with another sdk such as groovy, scala, ant for related information. As always you can explore options by issuing sdk --help
All of the installations are stored inside $SDKMAN_DIR/candidates from where we can select the default version sdk default $language $version or even select one for just the current terminal session sdk use $language $version.
Now that we have a very easy package manager for JVM languages lets go about installing java-9 so that we can use Jshell which is the REPL (Read, evaluate, print, repeat) feature to interact with JVM. No need to write a beautiful class with main object just so you can experiment with some esoteric String method.
Finding what java versions are supported
sdk list java
================================================================================
Available Java Versions
================================================================================
> * 9.0.7-zulu
9.0.4-openjdk
8.0.172-zulu
8.0.171-oracle
7.0.181-zulu
6.0.107-zulu
10.0.1-zulu
10.0.1-oracle
10.0.0-openjdk
1.0.0-rc1-graal
================================================================================
+ - local version
* - installed
> - currently in use
For our example let’s install zulu java-9.
sdk install java 9.0.7-zulu
If you don’t want to mess around with your system, don’t make it as the default one yet. Now java-9 can be found under ~/.sdkman/candidates/java. Jshell resides inside bin directory along with other java programs like java javac javadoc.
Make it executable by issuing: sudo chmod +x jshell
For ease of use we can create a symlink to this executable so that we can invoke it from anywhere in the system.
sudo ln -s ~/.sdkman/candidates/java/9.0.7-zulu/bin/jshell /usr/local/bin/jshell
Now we are ready to launch jshell and explore all the REPL beauty that it brings along.
jshell
You can now get your hands dirty