Java 9 REPL (JShell): Interactief coderen & testen vereenvoudigd

REPL staat voor Read-Eval-Print Loop. Met JShell heeft Java REPL-mogelijkheden. Met REPL kunt u Java-logica coderen en testen zonder te compileren met javac en direct het resultaat van berekeningen zien.

JShell starten

Open opdrachtprompt en typ jshell.

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

JShell-commando's bekijken

Typ /help zodra jshell draait.

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

JShell-commando uitvoeren

Typ /imports om de standaardimports te zien.

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>

Berekeningen in JShell

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

Functies aanmaken en gebruiken in JShell

Maak een functie doubled() die een int verdubbelt:

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

JShell afsluiten

Typ /exit.

jshell> /exit
| Goodbye