OnJava8/book/02-Installing-Java-and-the-Book-Examples.md

第二章 安装Java和本书用例

现在，我们来为这次阅读之旅作些准备吧！

在开始学习 Java 之前，你必须要先安装好 Java 和本书的源代码示例。因为考虑到可能有“专门的初学者”从本书开始学习编程，所以我会仔细解释计算机命令行 Shell 的这个过程。 如果你已经有此方面的经验了，可以跳过这段安装说明。如果你对此处描述的任何术语或过程仍不清楚，还可以通过 Google 搜索找到答案。具体的问题或困难请试着在 StackOverflow 上提问。或者去 YouTube 看有没有相关的安装说明。

编辑器

To create and modify Java program files—the code listings shown in this book—you need a program called an editor. You’ll also need an editor to make changes to your system configuration files, which is sometimes required during installation. Programming editors vary from heavyweight Integrated Development Environments (IDEs, like Eclipse, NetBeans and IntelliJ IDEA) to more basic text manipulation applications. If you already have an IDE and are comfortable with it, feel free to use that for this book, but in the interest of keeping things simple, I recommend the Atom editor. Find it at atom.io. Atom is free and open-source, is very simple to install, works on all platforms (Windows, Mac and Linux), and has a built-in Java mode that is automatically invoked when you open a Java file. It isn’t a heavy-duty IDE so it doesn’t get confusing, which is ideal for this book. On the other hand, it has some handy editing features that you’ll probably come to love. More details are on their site. There are many other editors; these are a subculture unto themselves and people even get into heated arguments about their merits. If you find one you like better, it’s not too hard to change. The important thing is to choose one and get comfortable with it.

Shell

If you haven’t programmed before, you might be unfamiliar with your operating system shell (also called the command prompt in Windows). The shell harkens back to the early days of computing when everything happened by typing commands and the computer responded by displaying responses; it was all text-based. Although it can seem primitive in the age of graphical user interfaces, a shell provides a surprising number of valuable features. We’ll use the shell regularly in this book, both as part of the installation process and to run Java programs. Starting a Shell Mac: Click on the Spotlight (the magnifying-glass icon in the upper- right corner of the screen) and type “terminal.” Click on the application that looks like a little TV screen (you might also be able to hit “Return”). This starts a shell in your home directory. Windows: First, start the Windows Explorer to navigate through your directories: Windows 7: click the “Start” button in the lower left corner of the screen. In the Start Menu search box area type “explorer” then press the “Enter” key. Windows 8: click Windows+Q, type “explorer” then press the “Enter” key. Windows 10: click Windows+E. Once the Windows Explorer is running, move through the folders on your computer by double-clicking on them with the mouse. Navigate to the desired folder. Now click the file tab at the top left of the Explorer window and select “Open command prompt.” This opens a shell in the destination directory. Linux: To open a shell in your home directory: Debian: Press Alt+F2. In the dialog that pops up, type ‘gnome- terminal’ Ubuntu: Either right-click on the desktop and select ‘Open Terminal’, or press Ctrl+Alt+T Redhat: Right-click on the desktop and select ‘Open Terminal’ Fedora: Press Alt+F2. In the dialog that pops up, type ‘gnome- terminal’ Directories Directories are one of the fundamental elements of a shell. Directories hold files, as well as other directories. Think of a directory as a tree with branches. If books is a directory on your system and it has two other directories as branches, for example math and art, we say you have a directory books with two subdirectories math and art. We refer to them as books/math and books/art since books is their parent directory. Note that Windows uses backslashes rather than forward slashes to separate the parts of a directory. Basic Shell Operations The shell operations I show here are approximately identical across operating systems. For the purposes of this book, here are the essential operations in a shell: Change directory: Use cd followed by the name of the directory where you want to move, or cd .. if you want to move up a directory. If you want to move to a different directory while remembering where you came from, use pushd followed by the different directory name. Then, to return to the previous directory, just say popd. Directory listing: ls (dir in Windows) displays all the files and subdirectory names in the current directory. Use the wildcard

• (asterisk) to narrow your search. For example, if you want to list all the files ending in “.java,” you say ls .java (Windows: dir .java). If you want to list the files starting with “F” and ending in “.java,” you say ls F.java (Windows: dir F.java). Create a directory: use the mkdir (“make directory”) command (Windows: md), followed by the name of the directory you want to create. For example, mkdir books (Windows: md books). Remove a file: Use rm (“remove”) followed by the name of the file you wish to remove (Windows: del). For example, rm somefile.java (Windows: del somefile.java). Remove a directory: use the rm -r command to remove the files in the directory and the directory itself (Windows: deltree). For example, rm -r books (Windows: deltree books). Repeat a command: The “up arrow” on all three operating systems moves through previous commands so you can edit and repeat them. On Mac/Linux, !! repeats the last command and !n repeats the nth command. Command history: Use history in Mac/Linux or press the F7 key in Windows. This gives you a list of all the commands you’ve entered. Mac/Linux provides numbers to refer to when you want to repeat a command. Unpacking a zip archive: A file name ending with .zip is an archive containing other files in a compressed format. Both Linux and Mac have command-line unzip utilities, and you can install a command-line unzip for Windows via the Internet. However, in all three systems the graphical file browser (Windows Explorer, the Mac Finder, or Nautilus or equivalent on Linux) will browse to the directory containing your zip file. Then right-mouse-click on the file and select “Open” on the Mac, “Extract Here” on Linux, or “Extract all …” on Windows. To learn more about your shell, search Wikipedia for Windows Shell or, for Mac/Linux, Bash Shell.

Java安装

To compile and run the examples, you must first install the Java development kit. In this book we use JDK8 (Java 1.8). Windows

1. Follow the instructions at this link to Install Chocolatey.
2. At a shell prompt, type: choco install jdk8. This takes some time, but when it’s finished Java is installed and the necessary environment variables are set. Macintosh The Mac comes with a much older version of Java that won’t work for the examples in this book, so you must first update it to Java 8. You will need administration rights to perform these steps.
3. Follow the instructions at this link to Install HomeBrew. Then at a shell prompt, execute brew update to make sure you have the latest changes.
4. At a shell prompt, execute brew cask install java. Once HomeBrew and Java are installed, all other activities described in this book can be accomplished within a guest account, if that suits your needs. Linux Use the standard package installer with the following shell commands: Ubuntu/Debian:
5. sudo apt-get update
6. sudo apt-get install default-jdk Fedora/Redhat:
7. su-c "yum install java-1.8.0-openjdk"

校验安装

Open a new shell and type: java -version You should see something like the following (Version numbers and actual text will vary): java version "1.8.0_112" Java(TM) SE Runtime Environment (build 1.8.0_112-b15) Java HotSpot(TM) 64-Bit Server VM (build 25.112-b15, mixed mode) If you see a message that the command is not found or not recognized, review the installation instructions in this chapter. If you still can’t get it to work, check StackOverflow.

安装和运行本书用例

Once you have Java installed, the process to install and run the book examples is the same for all platforms:

1. Download the book examples from the GitHub Repository.
2. unzip (as described in Basic Shell Operations) the downloaded file into the directory of your choice.
3. Use the Windows Explorer, the Mac Finder, or Nautilus or equivalent on Linux to browse to the directory where you unzipped OnJava8-Examples, and open a shell there.
4. If you’re in the right directory, you should see files named gradlew and gradlew.bat in that directory, along with numerous other files and directories. The directories correspond to the chapters in the book.
5. At the shell prompt, type gradlew run (Windows) or ./gradlew run (Mac/Linux). The first time you do this, Gradle will install itself and numerous other packages, so it will take some time. After everything is installed, subsequent builds and runs are faster. Note you must be connected to the Internet the first time you run gradlew so that Gradle can download the necessary packages. Basic Gradle Tasks There are a large number of Gradle tasks automatically available with this book’s build. Gradle uses an approach called convention over configuration which results in the availability of many tasks even if you’re only trying to accomplish something very basic. Some of the tasks that “came along for the ride” with this book are inappropriate or don’t successfully execute. Here is a list of the Gradle tasks you will typically use: gradlew compileJava: Compiles all the Java files in the book that can be compiled (some files don’t compile, to demonstrate incorrect language usage). gradlew run: First compiles, then executes all the Java files in the book that can be executed (some files are library components). gradlew test: Executes all the unit tests (you’ll learn about these in Validating Your Code). gradlew chapter: ExampleName: Compiles and runs a specific example program. For instance, gradlew objects:HelloDate.