What is JShell?

JShell is a new tool introduced with Java 9. It is an interactive read-eval-print loop tool that is used to evaluate the following Java programming language components--declarations, statements, and expressions. It has its own API so that it can be used by external applications.

Read-Eval-Print Loop is often referred to as REPL, taking the first letter from each word in the phrase. It is also knows language shell or interactive top-level.

The introduction of JShell was a result of Java Enhancement Program (JEP) 222. Here are the stated goals of this JEP in regards to the Java Shell command-line tool:

Facilitate rapid investigation
Facilitate rapid coding
Provide an edit history

The rapid investigation and coding listed previously includes statements and expressions. Impressively, these statements and expressions do not need to be part of a method. Furthermore, variables and methods are not required to be part of a class, making this tool especially dynamic.

In addition, the following listed features were included to make JShell much easier to use and to make your time using JShell as time-efficient as possible:

Tab-completion
Auto-completion for end-of-statement semicolons
Auto-completion for imports
Auto-completion for definitions

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