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jdk入门_JDK 9 REPL：入门

發布時間：2023/12/3 编程问答 51 豆豆

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jdk入門

會議是聚會Java名人的好地方。 Devoxx France是與Java語言架構師，前同事和老朋友Brian Goetz（ @briangoetz ）見面的一個機會。我們談論了JDK 9，而他全都熱衷于REPL。他提到，盡管Java SE 9中有很多重要功能，例如模塊化和HTTP2客戶端，但該工具將是最常被談論的。該聲明之所以有意義，是因為它將真正簡化Java API的探索，原型開發，會議中的演示以及類似任務，并且更加簡單。這個博客來自我們在那里的討論以及他對REPL的強烈投票！

Read-Evaluate-Print-Loop在Lisp，Python，Ruby，Groovy，Clojure和其他語言中已經存在了一段時間。 Unix shell是一個REPL，可以讀取shell命令，評估它們，打印輸出并返回循環以執行相同的操作。

您可以在JEP 222中的JDK 9中閱讀有關REPL的全部信息。 JEP的摘要是：

提供一個交互式工具，該工具可以評估Java編程語言的聲明，語句和表達式：即，提供Java編程語言的讀取-評估-打印循環（REPL）。另外，提供在其上構建工具的API，從而使外部工具能夠提供此功能。杰普222

JEP還明確闡明了動機：

沒有Foo類{public static void main（String [] args）{…}}的儀式，學習和探索就變得簡化了。杰普222

JEP 222的目標是將REPL與JDK 9一起提供，但openjdk.java.net/projects/jdk9并未將其列為“目標”或“建議目標”。好像是一個文檔錯誤:)

從JDK 9 build 61開始，REPL未集成，需要單獨構建。最終，在發布JDK 9之前的某個時間，此工具將集成到內部版本中。

讓我們看看在OSX上運行它需要什么。該博客遵循Java 9 REPL –入門指南來構建和運行REPL。此外，它還提供了命令的完整日志輸出，這可能對某些人有幫助。

讓我們開始吧！

安裝JDK 9

在撰寫本文時，下載最新的版本 61。

將JAVA_HOME設置為： export JAVA_HOME=`/usr/libexec/java_home -v1.9`

在OSX上設置JAVA_HOME的更多詳細信息在這里。

驗證版本： ~> java -version java version "1.9.0-ea" Java(TM) SE Runtime Environment (build 1.9.0-ea-b61) Java HotSpot(TM) 64-Bit Server VM (build 1.9.0-ea-b61, mixed mode)

檢出并安裝jline2

jline2是一個用于處理控制臺輸入的Java庫。看看這個：

workspaces> git clone git://github.com/jline/jline2.git Cloning into 'jline2'... remote: Counting objects: 6419, done. remote: Total 6419 (delta 0), reused 0 (delta 0), pack-reused 6419 Receiving objects: 100% (6419/6419), 3.23 MiB | 80.00 KiB/s, done. Resolving deltas: 100% (2945/2945), done. Checking connectivity... done.

然后構建它：

jline2> mvn install [INFO] Scanning for projects... Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/scm/maven-scm-provider-gitexe/1.8.1/maven-scm-provider-gitexe-1.8.1.pom Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/scm/maven-scm-provider-gitexe/1.8.1/maven-scm-provider-gitexe-1.8.1.pom (3 KB at 0.3 KB/sec). . .[INFO] Installing /Users/arungupta/workspaces/jline2/target/jline-2.13-SNAPSHOT-sources.jar to /Users/arungupta/.m2/repository/jline/jline/2.13-SNAPSHOT/jline-2.13-SNAPSHOT-sources.jar [INFO] Installing /Users/arungupta/workspaces/jline2/target/jline-2.13-SNAPSHOT-tests.jar to /Users/arungupta/.m2/repository/jline/jline/2.13-SNAPSHOT/jline-2.13-SNAPSHOT-tests.jar [INFO] ------------------------------------------------------------------------ [INFO] BUILD SUCCESS [INFO] ------------------------------------------------------------------------ [INFO] Total time: 09:52 min [INFO] Finished at: 2015-05-06T19:23:14-07:00 [INFO] Final Memory: 25M/146M [INFO] ------------------------------------------------------------------------

克隆并構建JDK 9 REPL

該項目的OpenJDK代號為Kulla，意為“建設者之神”。該工具的計劃名稱為jshell 。

簽出工作區： workspaces> hg clone http://hg.openjdk.java.net/kulla/dev kulla requesting all changes adding changesets adding manifests adding file changes added 1453 changesets with 2226 changes to 172 files updating to branch default 109 files updated, 0 files merged, 0 files removed, 0 files unresolved

獲取來源： workspaces> cd kulla kulla> chmod +x ./get_source.sh kulla> ./get_source.sh # Repositories: corba jaxp jaxws langtools jdk hotspot nashorn corba: hg clone http://hg.openjdk.java.net/kulla/dev/corba corbajaxp: hg clone http://hg.openjdk.java.net/kulla/dev/jaxp jaxpcorba: requesting all changesjaxp: requesting all changescorba: adding changesetsjaxp: adding changesetscorba: adding manifestsjaxp: adding manifestscorba: adding file changesjaxp: adding file changescorba: added 669 changesets with 4913 changes to 2576 filescorba: updating to branch defaultcorba: 1184 files updated, 0 files merged, 0 files removed, 0 files unresolvedjaxws: hg clone http://hg.openjdk.java.net/kulla/dev/jaxws jaxwsjaxws: requesting all changesjaxws: adding changesetsjaxws: adding manifestsjaxws: adding file changesjaxp: added 728 changesets with 10192 changes to 7393 filesjaxp: updating to branch defaultjaxp: 3044 files updated, 0 files merged, 0 files removed, 0 files unresolvedlangtools: hg clone http://hg.openjdk.java.net/kulla/dev/langtools langtoolslangtools: requesting all changeslangtools: adding changesetslangtools: adding manifestsjaxws: added 589 changesets with 20521 changes to 10746 filesjaxws: updating to branch defaultjaxws: 3750 files updated, 0 files merged, 0 files removed, 0 files unresolvedjdk: hg clone http://hg.openjdk.java.net/kulla/dev/jdk jdklangtools: adding file changesjdk: requesting all changesjdk: adding changesetsjdk: adding manifestslangtools: added 3173 changesets with 28112 changes to 9103 fileslangtools: updating to branch defaultlangtools: 7100 files updated, 0 files merged, 0 files removed, 0 files unresolvedhotspot: hg clone http://hg.openjdk.java.net/kulla/dev/hotspot hotspothotspot: requesting all changeshotspot: adding changesetshotspot: adding manifestshotspot: adding file changeshotspot: added 8073 changesets with 45889 changes to 6290 fileshotspot: updating to branch defaulthotspot: 5030 files updated, 0 files merged, 0 files removed, 0 files unresolvednashorn: hg clone http://hg.openjdk.java.net/kulla/dev/nashorn nashornnashorn: requesting all changesnashorn: adding changesetsnashorn: adding manifestsjdk: adding file changesnashorn: adding file changesnashorn: added 1252 changesets with 11596 changes to 3595 filesnashorn: updating to branch defaultnashorn: 2867 files updated, 0 files merged, 0 files removed, 0 files unresolvedjdk: added 11805 changesets with 116593 changes to 42135 filesjdk: updating to branch defaultjdk: 23192 files updated, 0 files merged, 0 files removed, 0 files unresolved # Repositories: . corba jaxp jaxws langtools jdk hotspot nashorn .: cd . && hg pull -ucorba: cd corba && hg pull -ujaxp: cd jaxp && hg pull -ujaxws: cd jaxws && hg pull -ulangtools: cd langtools && hg pull -ujdk: cd jdk && hg pull -uhotspot: cd hotspot && hg pull -unashorn: cd nashorn && hg pull -ujaxws: pulling from http://hg.openjdk.java.net/kulla/dev/jaxwscorba: pulling from http://hg.openjdk.java.net/kulla/dev/corbalangtools: pulling from http://hg.openjdk.java.net/kulla/dev/langtoolshotspot: pulling from http://hg.openjdk.java.net/kulla/dev/hotspotjdk: pulling from http://hg.openjdk.java.net/kulla/dev/jdk.: pulling from http://hg.openjdk.java.net/kulla/devjaxp: pulling from http://hg.openjdk.java.net/kulla/dev/jaxpnashorn: pulling from http://hg.openjdk.java.net/kulla/dev/nashornnashorn: searching for changesnashorn: no changes foundjaxws: searching for changesjaxws: no changes foundjaxp: searching for changesjaxp: no changes foundcorba: searching for changescorba: no changes foundjdk: searching for changeshotspot: searching for changeshotspot: no changes foundjdk: no changes found.: searching for changes.: no changes foundlangtools: searching for changeslangtools: no changes found

編輯langtools/repl/scripts/compile.sh腳本，如下所示： #!/bin/sh JLINE2LIB=/Users/arungupta/workspaces/jline2/target/jline-2.13-SNAPSHOT.jar mkdir -p build javac -Xlint:unchecked -Xdiags:verbose -cp ${JLINE2LIB} -d build ../src/jdk.jshell/share/classes/*/*/*.java ../src/jdk.jshell/share/classes/*/*/*/*/*.java ../src/jdk.jshell/share/classes/*/*/*/*/*/*.java

注意，唯一的編輯是OSX的#!/bin/sh并將JLINE2LIB添加到先前編譯的jline2工作區的位置。從引用JDK 9的JAVA_HOME中拾取javac 。

通過從langtools/repl目錄調用腳本來編譯REPL工具： repl> chmod +x ./scripts/compile.sh repl> ./scripts/compile.sh

運行JDK 9 REPL

編輯langtools/repl/scripts/run.sh腳本，如下所示： #!/bin/sh JLINE2LIB=/Users/arungupta/workspaces/jline2/target/jline-2.13-SNAPSHOT.jar java -ea -esa -cp build:${JLINE2LIB} jdk.internal.jshell.tool.JShellTool "$@"

注意，對于OSX唯一的編輯是!/bin/sh并添加JLINE2LIB 。

將REPL運行為： repl> ./scripts/run.sh | Welcome to JShell -- Version 0.428 | Type /help for help

JDK 9 REPL Hello World

與引入Java的彈跳球或跳舞Duke引入不同，我們只將常規的Hello World用于REPL

將“ Hello World”運行為：

-> System.out.println("Hello World"); Hello World

瞧！

沒有public static void main ，沒有類的創建，沒有儀式，只是干凈而簡單的Java代碼。輸入的文本稱為“代碼段”。

可以使用/list all查看完整的Java代碼，如下所示：

-> /list all1 : import java.util.*;2 : import java.io.*;3 : import java.math.*;4 : import java.net.*;5 : import java.util.concurrent.*;6 : import java.util.prefs.*;7 : import java.util.regex.*;8 : void printf(String format, Object... args) { System.out.printf(format, args); }9 : System.out.println("Hello World");

該代碼段可以另存為文件：

-> /save test

請注意，這不是Java文件。保存的代碼段正是輸入的內容：

repl> more test System.out.println("Hello World");

該工具可以退出為：

-> /exit | Goodbye

或者您可以按Ctrl + C。

完整的命令列表很容易看到：

-> /help Type a Java language expression, statement, or declaration. Or type one of the following commands:/l or /list [all] -- list the source you have typed/seteditor <executable> -- set the external editor command to use /e or /edit <name or id> -- edit a source entry referenced by name or id /- or /drop <name or id> -- delete a source entry referenced by name or id /s or /save [all|history] <file> -- save the source you have typed /o or /open <file> -- open a file as source input /v or /vars -- list the declared variables and their values /m or /methods -- list the declared methods and their signatures /c or /classes -- list the declared classes /x or /exit -- exit the REPL /r or /reset -- reset everything in the REPL /f or /feedback <level> -- feedback information: off, concise, normal, verbose, default, or ? /p or /prompt -- toggle display of a prompt /cp or /classpath <path> -- add a path to the classpath /h or /history -- history of what you have typed/setstart <file> -- read file and set as the new start-up definitions/savestart <file> -- save the default start-up definitions to the file /? or /help -- this help messageSupported shortcuts include: <tab> -- show possible completions for the current text Shift-<tab> -- for current method or constructor invocation, show a synopsis of the method/constructor

JDK 9 REPL后續步驟和反饋

請遵循REPL教程以了解有關該工具功能的更多信息。快速概述：

接受Java語句，變量，方法和類的定義，導入和表達式
設置和顯示信息的命令，例如/list顯示代碼片段列表， /vars顯示變量列表， /save保存代碼片段， /open讀回它們。
片段的歷史記錄可用，片段可以按數字進行編輯，等等

這是一個有用的RFE：

將代碼段導出為完整的Java類

隨后的博客將展示如何將其用于Java EE應用程序的播放。您將如何使用REPL？

在kulla-dev上討論項目/問題。

請享用！

翻譯自: https://www.javacodegeeks.com/2015/05/jdk-9-repl-getting-started.html