As of now, Java 9 official release date is 27.07.2017. According to openJDK mailing list the push back was due to the most anticipated feature of Java 9, which is the modularisation of the JDK or commonly known as Project Jigsaw.

I am not as much excited for this feature as I am for the brand new JShell. Many people criticise the language’s verbosity and sometimes the amount of code that is required to do some stuff. I do not disagree that this, in many cases, is true. But, what I was missing mainly from Java was the ability to quickly evaluate an expression/algorithm/piece of code.

For example, many times I find myself needing to try something quick which involves reading a file or reading something from the web and performing some manipulation on it. Or even sometimes testing out a lambda expression to see its behaviour. Up to this point, actions like that were a bit cumbersome, as it involved the creation of a class, a main method and the execution of that program.

JShell is introduced to solve problems like that and more. Also known as Project Kulla JShell is an extremely useful tool. It is a REPL (Read Evaluate Print Loop) tool. Similar ones exist in various other languages like Python, Perl, even Scala.

For someone to use JShell she/he needs to download JDK 9. Then all she/he has to do is to navigate to /bin directory and execute the jshell command.

Firstly, the JShell itself prompts the user to type /help intro

The jshell comes with auto-completion features, so the user can press Tab and see a list of commands depending on the first letter she/he typed:

A list of help command can appear on the output by typing /help.

By default JShell has to import the classes that the user is going to use. It comes with a pre-defined set of common classes already imported:

A user can import any JDK class, or even her/his own classes by adding to the classpath:

As someone can notice it is not mandatory to add semicolons in the end of statements. However, it is mandatory to add them if the user adds a class or a method.

Each expression the user writes on the console is evaluated and printed on the standard output. If an expression has a return type that return type is automatically assigned in a variable that the shell creates on the fly. Of course, later on the user can make use of that variable as normal:

User can define methods outside of classes. Additionally, classes can be defined and referenced as normal:

A very nice feature is the fact that the user does not need any try{}catch{} blocks for methods which define checked exceptions:

Finally, the user can see the defined methods, types and variables and reset her/his session:

Concluding, I believe JShell will be a nice to have tool. By exploring it I am pretty sure people will come up with some interesting uses of it.

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