jShell is a Java REPL planned to be introduced in the JDK 9. It is tracked by JEP 222: jshell: The Java Shell (Read-Eval-Print Loop).
One of the reasons jShell was proposed for Java 9 is that a lot of applications use their own mechanisms to interactively evaluate expressions, and the de facto library to use a Java REPL was often BeanShell, which is a dormant project since 2003, and which made arbitrary changes to the Java language.
Example
jshell> int x=5 x ==> 5 | created variable x : int jshell> x x ==> 5 | value of x : intReferences
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