Java9新特性之命令行交互式解释器JShell全解析

$ jshell
Feb 26, 2024 2:30:09 PM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
|  Welcome to JShell -- Version 18.0.1.1
|  For an introduction type: /help intro

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
|  /drop <name or id>
|       delete a source entry
|  /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 type declarations
|  /imports
|       list the imported items
|  /exit [<integer-expression-snippet>]
|       exit the jshell tool
|  /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 the jshell tool
|  /reload [-restore] [-quiet] [-class-path <path>] [-module-path <path>]...
|       reset and replay relevant history -- current or previous (-restore)
|  /history [-all]
|       history of what you have typed
|  /help [<command>|<subject>]
|       get information about using the jshell tool
|  /set editor|start|feedback|mode|prompt|truncation|format ...
|       set configuration information
|  /? [<command>|<subject>]
|       get information about using the jshell tool
|  /!
|       rerun last snippet -- see /help rerun
|  /<id>
|       rerun snippets by ID or ID range -- see /help rerun
|  /-<n>
|       rerun n-th previous snippet -- see /help rerun
|
|  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
|  keys
|       a description of readline-like input editing
|  id
|       a description of snippet IDs and how use them
|  shortcuts
|       a description of keystrokes for snippet and command completion,
|       information access, and automatic code generation
|  context
|       a description of the evaluation context options for /env /reload and /reset
|  rerun
|       a description of ways to re-evaluate previously entered snippets

jshell> /help intro
|
|                                   intro
|                                   =====
|
|  The jshell tool allows you to execute Java code, getting immediate results.
|  You can enter a Java definition (variable, method, class, etc), like:  int x = 8
|  or a Java expression, like:  x + x
|  or a Java statement or import.
|  These little chunks of Java code are called 'snippets'.
|
|  There are also the jshell tool commands that allow you to understand and
|  control what you are doing, like:  /list
|
|  For a list of commands: /help

jshell> /help /list
|
|                                   /list
|                                   =====
|
|  Show the snippets, prefaced with their snippet IDs.
|
|  /list
|       List the currently active snippets of code that you typed or read with /open
|
|  /list -start
|       List the evaluated startup snippets
|
|  /list -all
|       List all snippets including failed, overwritten, dropped, and startup
|
|  /list <name>
|       List snippets with the specified name (preference for active snippets)
|
|  /list <id>
|       List the snippet with the specified snippet ID.
|       One or more IDs or ID ranges may used, see '/help id'

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> import java.time.*
jshell> /import
|    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.*
|    import java.time.*

jshell> /env -class-path /root/hutool-all-5.8.12.jar
|  Setting new options and restoring state.
jshell> import cn.hutool.core.util.*
jshell> StrUtil.isBlankIfStr("abc")
$2 ==> false

jshell> 5 * 6
$2 ==> 30
jshell> $2
$2 ==> 30
jshell> 10 * $2
$4 ==> 300
jshell> int a = $4
a ==> 300
jshell> a
a ==> 300

jshell> Thread.currentThread()
$7 ==> Thread[main,5,main]

jshell> int add(int a, int b) { return a + b;}
|  created method add(int,int)
jshell> add(3,4)
$10 ==> 7

jshell> int sub(int a, int b) {
   ...>     return a - b;
   ...> }
|  created method sub(int,int)
jshell> sub(10, 5)
$12 ==> 5

jshell> /exit
|  Goodbye

jshell> exit
|  Error:
|  cannot find symbol
|    symbol:   variable exit
|  exit
|  ^--^