Java 9 REPL (JShell)

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

以下实例执行 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