如何在Java 9中获取JShell文档？

Java 9 引入了一种新的交互式工具，称为JShell。该工具可用于执行表达式、类、接口、枚举等。

详细的文档可以在 JShell 中找到，其中包含完整信息，以及使用其内部命令和各种选项的信息。可以使用两个命令访问此文档：“/help”和“/?”。 JShell的文档不仅限于其内部控制的信息，还包括Javadoc。

在下面的代码片段中，可以通过使用“ /help”命令。

<strong>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 [<names or id>|-all|-start]
|     list the declared types
|   /imports
|     list the imported items
|   /exit
|     exit jshell
|   /env [-class-path <path> ] [-module-path <path>] [-add-modules <modules>] ...
|     view or change the evaluation context
|   /reset [-class-path <path>] [-module-path <path>] [-add-modules <modules>]...
|     reset jshell
|   /reload [-restore] [-quiet] [-class-path <path>] [-module-path <path>]...
|     reset and replay relevant history -- current or previous (-restore)
|   /history
|     history of what you have typed
|   /help [<command>|<subject>]
|     get information about jshell
|   /set editor|start|feedback|mode|prompt|truncation|format ...
|     set jshell configuration information
|   /? [<command>|<subject> ]
|     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 completion,
|     information access, and automatic code generation
|   context
|     the evaluation context options for /env /reload and /reset</strong>

JShell 打印不同的现有内部命令，并快速介绍它们的用途，并访问其使用的更详细说明。为此，我们只需输入命令：“/help”，然后输入详细的命令名称（例如“/set”命令）。

<strong>jshell> /help /set
|
|  /set
|
|   Set jshell configuration information, including:
|   the external editor to use, the start-up definitions to use, a new feedback mode,
|   the command prompt, the feedback mode to use, or the format of output.
|
|   /set editor [-wait] ...
|     Specify the command to launch for the /edit command.
|     The <command> is an operating system dependent string.
|
|   /set start <file>
|     The contents of the specified become the default start-up snippet s and commands.
|
|   /set feedback <mode>
|     Set the feedback mode describing displayed feedback for entered snippets and commands.
|
|   /set mode <mode>[<old-mode>] -command|-quiet|-delete
|     Create or update a user-defined feedback mode, optionally copying from an existing mode.
|
|   /set prompt <mode>"<prompt>" "<continuation-prompt>"
|     Set the displayed prompts for a given feedback mode.
|
|   /set truncation <mode> <length> <selector> ...
|     Set the maximum length of a displayed value.
|
|   /set format <mode> <field> "<format>" ...
|     Configure a feedback mode by setting the format of a field when the selector matches.
|
|   /set
|     Show editor, start, and feedback settings as /set commands.
|     To show the settings of any of the above, omit the set value.
|
|     To get more information about one of these forms, use /help with the form specified.
|  For example: /help /set format</strong>

我们需要找到第三部分输入的命令，是否修改JShell的返回（/set Feedback），以修改默认编辑器（/set editor），或者修改JShell的启动（/set start）。

<strong>jshell> /help /set feedback
| Set the feedback mode describing displayed feedback for entered snippets and
commands:
|
| /set feedback [-retain] <mode>
|
| Retain the current feedback mode for future sessions:
|
| /set feedback -retain
|
| Show the feedback mode and list available modes:
|
| /set feedback
|
| Where <mode> is the name of a previously defined feedback mode.
| You may use just enough letters to make it unique.
| User-defined modes can be added, see &#39;/help /set mode&#39;
|
| When the -retain option is used, the setting will be used in this and future
| runs of the jshell tool.
|
| The form without <mode> or -retain displays the current feedback mode and available modes.</strong>

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