Java 9 REPL (JShell)

REPL代表Read-Eval-Print Loop。有了JShell，Java也具备了REPL功能。使用REPL，我们可以编写和测试基于Java的逻辑，而无需使用javac进行编译，并直接查看计算结果。

运行JShell

打开命令提示符并输入jshell。

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

查看JShell命令

在JShell命令开始运行时，输入/help。

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

运行JShell命令

一旦运行JShell命令，输入/imports来查看已使用的导入。

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>

在JShell中运行计算。

尝试在JShell中运行简单的计算。

jshell> 3+1
1 ==> 4
jshell> 13%72 ==> 6
jshell> 22 ==> 6
jshell>

在JShell中创建和使用函数

创建一个名为doubled()的函数，接受一个整数并返回它的两倍值。

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

退出JShell

输入/exit。

jshell> /exit
| Goodbye