Java 9 is introducing jshell,a tool added to 'bin' of JDK.
It provides, the feature of executing java programs(statements) on the fly,without the need to write class,main method etc.
Many languages like R,Scala already have REPL (Read,Evaluate,Print,Loop) feature.
So it will be not only easy for developing prototypes, POC(proof of concepts) for professionals,but also,it will be helpful for the beginners and new learners to learn the language easily and rapidly.
Java statements can be executed instantly, by running jshell on the command prompt.
To install JDK 9 click
To view jshell commands