May 2025
Intermediate to advanced
552 pages
7h 22m
Chinese
Content preview from 学习 Java，第 6 版
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第 3 章 交易工具 贸易工具
本作品已使用人工智能进行翻译。欢迎您提供反馈和意见：translation-feedback@oreilly.com
虽然您几乎肯定会在 VS Code 或 IntelliJ IDEA 等集成开发环境中完成大部分 Java 开发工作，但您在"安装 JDK "中下载的 JDK 中包含了构建 Java 应用程序所需的所有核心工具。当我们编写 Java 源代码时，是 Java 编译器-javac将我们的源代码转化为可用的字节码。当我们要测试字节码时，我们使用 Java 命令本身-java-来执行我们的程序。当我们编译好所有的类并使其协同工作时，Java 归档工具-jar-就可以让我们将这些类捆绑起来进行发布。 在本章中，我们将讨论其中一些命令行工具，您可以使用它们来编译、运行和打包 Java 应用程序。JDK 中还包含许多其他开发工具，如用于交互工作的jshell或用于反编译类文件的javap。我们没有时间在本书中讨论所有这些工具，但只要其他工具可能有用，我们都会提及。(我们一定会介绍jshell。它是快速试用新类或新方法的好帮手）。
我们希望即使您通常不在终端或命令窗口中工作，也能熟练使用这些命令行工具。这些工具的某些功能无法通过集成开发环境轻松访问。您可能还会遇到集成开发环境不实用或根本无法使用的情况。例如，系统管理员和 DevOps 工程师通常只能与运行在高级数据中心的服务器进行有限的、基于文本的连接。如果您需要通过这种连接解决 Java 问题，这些命令行工具将是必不可少的。
JDK 环境
在您安装 JDK 后，核心java运行时命令通常会自动出现在您的路径中（可运行），但并非总是如此。此外，除非您在执行路径中添加 Javabin目录，否则 JDK 提供的许多其他命令可能无法使用。为了确保您能访问所有工具，无论您的设置如何，以下命令展示了如何在 Linux、macOS 和 Windows 上正确配置您的开发环境。您需要为 Java 的位置定义一个新的环境变量，并将bin文件夹追加到现有的路径变量中。(操作系统使用环境变量来存储应用程序可以使用并可能在运行时共享的信息）。当然，您必须更改示例中的路径，以匹配您安装的 Java 版本：
# Linux export JAVA_HOME=/usr/lib/jvm/jdk-21-ea14 export PATH=$PATH:$JAVA_HOME/bin # Mac OS X export JAVA_HOME=/Users/marc/jdks/jdk-21-ea14/Contents/Home export PATH=$PATH:$JAVA_HOME/bin # Windows set JAVA_HOME=c:\Program Files\Java\jdk21 set PATH=%PATH%;%JAVA_HOME%\bin
在 macOS 上，情况可能会更加混乱，因为最新版本的操作系统在出厂时已经安装了 Java 命令的 "存根"。苹果公司不再提供自己的 Java 实现，因此如果您尝试运行这些命令，操作系统会提示您下载 Java。
如有疑问，您可以使用java和javac命令上的-version 标志来测试 Java 是否已安装，以及您使用的是哪个版本的工具：
% java -version openjdk version "21-ea" 2023-09-19 OpenJDK Runtime Environment (build 21-ea+14-1161) OpenJDK 64-Bit ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.