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。
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>
第 2 步：JShell 命令窗口开始运行后，键入 /help（以查看 JShell 命令）。
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 '/help' followed by the name of a | command or a subject. | For example '/help /list' or '/help intro'. | | 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
第三步：在JShell命令窗口中输入 /imports，获取JShell导入的包。
立即学习“Java免费学习笔记（深入）”；
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.*
第 4 步：在 JShell 中执行计算（尝试使用 JShell 进行算术计算）
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
第 5 步：要退出 JShell，请输入 /exit。
jshell> /exit | Goodbye
