JShell in Java 9?

JShell是 Java 9 版本中引入的新概念。它为 Java 提供了REPL（Read-Eval-Print-Loop）能力。通过使用 JShell，我们可以测试基于 Java 的逻辑和表达式，而无需编译它。 REPL 充当即时反馈循环，对特定语言的生产力有很大影响。

第 1 步：打开命令提示符并输入 JShell。

<strong>Microsoft Windows [Version 6.3.9600]
(c) 2013 Microsoft Corporation. All rights reserved.

C:\Users\User>JShell
| Welcome to JShell -- Version 9.0.4
| For an introduction type: /help intro

jshell></strong>

第 2 步：JShell 命令窗口开始运行后，键入 /help（以查看 JShell 命令）。

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

| reset jshell
| /reload [-restore] [-quiet] [-class-path ] [-module-path
| reset and replay relevant history -- current or previous (
| /history
| history of what you have typed
| /help [|]
| get information about jshell
| /set editor|start|feedback|mode|prompt|truncation|format ...
| set jshell configuration information
| /? [|]
| get information about jshell
| /!
| re-run last snippet
| /
| re-run snippet by id
| /-
| re-run n-th previous snippet
|
| For more information type &#39;/help&#39; followed by the name of a
| command or a subject.
| For example &#39;/help /list&#39; or &#39;/help intro&#39;.
|
| Subjects:
|
| intro
| an introduction to the jshell tool
| shortcuts
| a description of keystrokes for snippet and command comple
| information access, and automatic code generation
| context
| the evaluation context options for /env /reload and /reset</strong>

第三步：在JShell命令窗口中输入 /imports，获取JShell导入的包。

<strong>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.*</strong>

第 4 步：在 JShell 中执行计算（尝试使用 JShell 进行算术计算）

<strong>jshell> 3+5
$1 ==> 8

jshell> 8-4
$2 ==> 4

jshell> 2*6
$3 ==> 12

jshell> 9%3
$4 ==> 0

jshell> 8/2
$5 ==> 4</strong>

第 5 步：要退出 JShell，请输入 /exit。

<strong>jshell> /exit
| Goodbye</strong>

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