Java 9 REPL (JShell)

Java 9 New Features

REPL (Read Eval Print Loop) means an interactive programming environment.

JShell is Java 9 A new interactive programming environment tool. It allows you to execute Java statements without using class or method wrapping. It is similar to Python's interpreter and can directly input expressions to view their execution results.

Execute JSHELL

$　jshell
|　　Welcome　to　JShell　--　Version　9-ea
|　　For　an　introduction　type:　/help　intro
jshell>

View JShell commands

Input 　/The 'help' command can be used to view JShell-related commands:

jshell>　/help
|　　Type　a　Java　language　expression,　statement,　or　declaration.
|　　Or　type　one　of　the　following　commands:
|　　/list　[<name　or　id>|-all|-start]
|　　list　the　source　you　have　typed
|　　/edit　<name　or　id>
|　　edit　a　source　entry　referenced　by　name　or　id
|　　/drop　<name　or　id>
|　　delete　a　source　entry　referenced　by　name　or　id
|　　/save　[-all|-history|-start]　<file>
|　　Save　snippet　source　to　a　file.
|　　/open　<file>
|　　open　a　file　as　source　input
|　　/vars　[<name　or　id>|-all|-start]
|　　list　the　declared　variables　and　their　values
|　　/methods　[<name　or　id>|-all|-start]
|　　list　the　declared　methods　and　their　signatures
|　　/types　[<name　or　id>|-all|-start]
|　　list　the　declared　types
|　　/imports　
|　　list　the　imported　items

Execute JShell command

/The 'imports' command is used to view imported packages:

jshell>　/imports
|　　import　java.io.*
|　　import　java.math.*
|　　import　java.net.*
|　　import　java.nio.file.*
|　　import　java.util.*
| Import java.util.concurrent.*
| Import java.util.function.*
| Import java.util.prefs.*
| Import java.util.regex.*
| Import java.util.stream.*
jshell>

JShell Executing Calculations

The following examples execute simple calculations in JShell:

jshell>　3+1
$1　==>　4
jshell>　13%7
$2　==>　6
jshell> $2
$2　==>　6
jshell>

JShell Creating and Using Functions

Create a function doubled() that multiplies the integer parameter by 2 after returning:

jshell> int doubled(int i){ return i*2;}
| Created method doubled(int)
jshell> doubled(6)
$3　==>　12
jshell>

Exit JShell

Input 　/The 'exit' command exits jshell:

jshell>　/exit
| Goodbye

Java 9 New Features