REPL(Read Eval Print Loop)意为交互式的编程环境。
JShell 是 Java 9 新增的一个交互式的编程环境工具。它允许你无需使用类或者方法包装来执行 Java 语句。它与 Python 的解释器类似，可以直接 输入表达式并查看其执行结果。
执行 JSHELL
$ jshell | Welcome to JShell -- Version 9-ea | For an introduction type: /help intro jshell>
查看 JShell 命令
输入 /help 可以查看 JShell相关的命令：
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
执行 JShell 命令
/imports 命令用于查看已导入的包：
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>
JShell 执行计算
以下示例执行 JShell 简单计算：
jshell> 3+1 $1 ==> 4 jshell> 13%7 $2 ==> 6 jshell> $2 $2 ==> 6 jshell>
JShell 创建与使用函数
创建一个函数 doubled() ，将传入的整型参数乘于 2 后返回：
jshell> int doubled(int i){ return i*2;}
| created method doubled(int)
jshell> doubled(6)
$3 ==> 12
jshell>退出 JShell
输入 /exit 命令退出 jshell：
jshell> /exit | Goodbye