jdk入门
会议是聚会Java名人的好地方。 Devoxx France是与Java语言架构师,前同事和老朋友Brian Goetz( @briangoetz )见面的一个机会。 我们谈论了JDK 9,而他全都热衷于REPL。 他提到,尽管Java SE 9中有很多重要功能 ,例如模块化和HTTP2客户端 ,但该工具将是最常被谈论的。 该声明之所以有意义,是因为它将真正简化Java API的探索,原型开发,会议中的演示以及类似任务,并且更加简单。 这个博客来自我们在那里的讨论以及他对REPL的强烈投票!
Read-Evaluate-Print-Loop在Lisp,Python,Ruby,Groovy,Clojure和其他语言中已经存在了一段时间。 Unix shell是一个REPL,可以读取shell命令,评估它们,打印输出并返回循环以执行相同的操作。
您可以在JEP 222中的JDK 9中阅读有关REPL的全部信息。 JEP的摘要是:
提供一个交互式工具,该工具可以评估Java编程语言的声明,语句和表达式:即,提供Java编程语言的读取-评估-打印循环(REPL)。 另外,提供在其上构建工具的API,从而使外部工具能够提供此功能。 杰普222
JEP还明确阐明了动机:
没有Foo类{public static void main(String [] args){…}}的仪式,学习和探索就变得简化了。 杰普222
JEP 222的目标是将REPL与JDK 9一起提供,但openjdk.java.net/projects/jdk9并未将其列为“目标”或“建议目标”。 好像是一个文档错误:)
从JDK 9 build 61开始,REPL未集成,需要单独构建。 最终,在发布JDK 9之前的某个时间,此工具将集成到内部版本中。
让我们看看在OSX上运行它需要什么。 该博客遵循Java 9 REPL –入门指南来构建和运行REPL。 此外,它还提供了命令的完整日志输出,这可能对某些人有帮助。
让我们开始吧!
安装JDK 9
- 在撰写本文时,下载最新的版本 61。
- 将JAVA_HOME设置为:
export JAVA_HOME=`/usr/libexec/java_home -v1.9`
在OSX上设置JAVA_HOME的更多详细信息在这里 。
- 验证版本:
~> 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)
检出并安装jline2
jline2是一个用于处理控制台输入的Java库。 看看这个:
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.
然后构建它:
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] ------------------------------------------------------------------------
克隆并构建JDK 9 REPL
该项目的OpenJDK代号为Kulla,意为“建设者之神”。 该工具的计划名称为jshell
。
- 签出工作区:
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
- 获取来源:
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
- 编辑
langtools/repl/scripts/compile.sh
脚本,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 ${JLINE2LIB} -d build ../src/jdk.jshell/share/classes/*/*/*.java ../src/jdk.jshell/share/classes/*/*/*/*/*.java ../src/jdk.jshell/share/classes/*/*/*/*/*/*.java
注意,唯一的编辑是OSX的
#!/bin/sh
并将JLINE2LIB
添加到先前编译的jline2
工作区的位置。 从引用JDK 9的JAVA_HOME中拾取javac
。 - 通过从
langtools/repl
目录调用脚本来编译REPL工具:repl> chmod +x ./scripts/compile.sh repl> ./scripts/compile.sh
运行JDK 9 REPL
- 编辑
langtools/repl/scripts/run.sh
脚本,如下所示:#!/bin/sh JLINE2LIB=/Users/arungupta/workspaces/jline2/target/jline-2.13-SNAPSHOT.jar java -ea -esa -cp build:${JLINE2LIB} jdk.internal.jshell.tool.JShellTool "$@"
注意,对于OSX唯一的编辑是
!/bin/sh
并添加JLINE2LIB
。 - 将REPL运行为:
repl> ./scripts/run.sh | Welcome to JShell -- Version 0.428 | Type /help for help
JDK 9 REPL Hello World
与引入Java的弹跳球或跳舞Duke引入不同,我们只将常规的Hello World用于REPL
将“ Hello World”运行为:
-> System.out.println("Hello World");
Hello World
瞧!
没有public static void main
,没有类的创建,没有仪式,只是干净而简单的Java代码。 输入的文本称为“代码段”。
可以使用/list all
查看完整的Java代码,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");
该代码段可以另存为文件:
-> /save test
请注意,这不是Java文件。 保存的代码段正是输入的内容:
repl> more test
System.out.println("Hello World");
该工具可以退出为:
-> /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后续步骤和反馈
请遵循REPL教程以了解有关该工具功能的更多信息。 快速概述:
- 接受Java语句,变量,方法和类的定义,导入和表达式
- 设置和显示信息的命令,例如
/list
显示代码片段列表,/vars
显示变量列表,/save
保存代码片段,/open
读回它们。 - 片段的历史记录可用,片段可以按数字进行编辑,等等
这是一个有用的RFE:
- 将代码段导出为完整的Java类
随后的博客将展示如何将其用于Java EE应用程序的播放。 您将如何使用REPL?
在kulla-dev上讨论项目/问题。
请享用!
翻译自: https://www.javacodegeeks.com/2015/05/jdk-9-repl-getting-started.html
jdk入门