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 '/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 completion, | information access, and automatic code generation | context | the evaluation context options for /env /reload and /reset</strong>
立即学习“Java免费学习笔记（深入）”；
立即学习“Java免费学习笔记（深入）”；
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>
立即学习“Java免费学习笔记（深入）”；
立即学习“Java免费学习笔记（深入）”；
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 '/help /set mode' | | 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>
