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Java™ 教程-Java Tutorials 中文版
"Hello World!" 应用
"Hello World!" for the NetBeans IDE
"Hello World!" for Microsoft Windows
"Hello World!" for Solaris OS and Linux
Trail: Getting Started
Lesson: The "Hello World!" Application
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"Hello World!" for the NetBeans IDE

现在是编写第一个应用程序的时候了！These detailed instructions are for users of the NetBeans IDE. The NetBeans IDE runs on the Java platform, which means that you can use it with any operating system for which there is a JDK available. These operating systems include Microsoft Windows, Solaris OS, Linux, and Mac OS X.

检查清单  a checkmark

要编写第一个程序，你需要：

  1. The Java SE Development Kit (JDK 7 has been selected in this example)

  2. The NetBeans IDE

创建你的第一个应用

Your first application, HelloWorldApp, will simply display the greeting "Hello World!" To create this program, you will:

Create an IDE Project

To create an IDE project:

  1. Launch the NetBeans IDE.

    • On Microsoft Windows systems, you can use the NetBeans IDE item in the Start menu.

    • On Solaris OS and Linux systems, you execute the IDE launcher script by navigating to the IDE's bin directory and typing ./netbeans.

    • On Mac OS X systems, click the NetBeans IDE application icon.

  2. In the NetBeans IDE, choose File | New Project....

    NetBeans IDE with the File | New Project menu item selected.

    NetBeans IDE with the File | New Project menu item selected.

  3. In the New Project wizard, expand the Java category and select Java Application as shown in the following figure:

    NetBeans IDE, New Project wizard, Choose Project page.

    NetBeans IDE, New Project wizard, Choose Project page.

  4. In the Name and Location page of the wizard, do the following (as shown in the figure below):

    • In the Project Name field, type Hello World App.

    • In the Create Main Class field, type helloworldapp.HelloWorldApp.

    NetBeans IDE, New Project wizard, Name and Location page.

    NetBeans IDE, New Project wizard, Name and Location page.

  5. Click Finish.

The project is created and opened in the IDE. You should see the following components:

Add JDK 8 to the Platform List (if necessary)

It may be necessary to add JDK 8 to the IDE's list of available platforms. To do this, choose Tools | Java Platforms as shown in the following figure:

Selecting the Java Platform Manager from the Tools Menu

Selecting the Java Platform Manager from the Tools Menu

If you don't see JDK 8 (which might appear as 1.8 or 1.8.0) in the list of installed platforms, click Add Platform, navigate to your JDK 8 install directory, and click Finish. You should now see this newly added platform:

The Java Platform Manager from the Tools Menu

The Java Platform Manager

To set this JDK as the default for all projects, you can run the IDE with the --jdkhome switch on the command line, or by entering the path to the JDK in the netbeans_j2sdkhome property of your INSTALLATION_DIRECTORY/etc/netbeans.conf file.

To specify this JDK for the current project only, select Hello World App in the Projects pane, choose File | Project Properties (Hello World App), click Libraries, then select JDK 1.8 in the Java Platform pulldown menu. You should see a screen similar to the following:

The IDE is now configured for JDK 8.

Add Code to the Generated Source File

When you created this project, you left the Create Main Class checkbox selected in the New Project wizard. The IDE has therefore created a skeleton class for you. You can add the "Hello World!" message to the skeleton code by replacing the line:

// TODO code application logic here

with the line:

System.out.println("Hello World!"); // Display the string.

Optionally, you can replace these four lines of generated code:

/**
 *
 * @author
 */

with these lines:

/**
 * The HelloWorldApp class implements an application that
 * simply prints "Hello World!" to standard output.
 */

These four lines are a code comment and do not affect how the program runs. Later sections of this tutorial explain the use and format of code comments.

Be Careful When You Type uppercase letter A   lowercase letter A

注意: 完全按照所示键入所有代码，命令和文件名。编译器(javac)和启动器(java)都是 case-sensitive，因此你必须一致地大写。

HelloWorldApp 与 helloworldapp 不相同。

Save your changes by choosing File | Save.

The file should look something like the following:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package helloworldapp;

/**
 * The HelloWorldApp class implements an application that
 * simply prints "Hello World!" to standard output.
 */
public class HelloWorldApp {

   
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        System.out.println("Hello World!"); // Display the string.
    }

}

将源文件编译为.class 文件

To compile your source file, choose Run | Build Project (Hello World App) from the IDE's main menu.

The Output window opens and displays output similar to what you see in the following figure:

Output window showing results of building the HelloWorld project.

Output window showing results of building the HelloWorld project.

If the build output concludes with the statement BUILD SUCCESSFUL, congratulations! You have successfully compiled your program!

If the build output concludes with the statement BUILD FAILED, you probably have a syntax error in your code. Errors are reported in the Output window as hyperlinked text. You double-click such a hyperlink to navigate to the source of an error. You can then fix the error and once again choose Run | Build Project.

When you build the project, the bytecode file HelloWorldApp.class is generated. You can see where the new file is generated by opening the Files window and expanding the Hello World App/build/classes/helloworldapp node as shown in the following figure.

Files window, showing the generated .class file.

Files window, showing the generated .class file.

Now that you have built the project, you can run your program.

运行程序

From the IDE's menu bar, choose Run | Run Main Project.

The next figure shows what you should now see.

The program prints Hello World! to the Output window (along with other output from the build script).

The program prints "Hello World!" to the Output window (along with other output from the build script).

恭喜！你的程序有效！

Continuing the Tutorial with the NetBeans IDE

The next few pages of the tutorial will explain the code in this simple application. After that, the lessons go deeper into core language features and provide many more examples. Although the rest of the tutorial does not give specific instructions about using the NetBeans IDE, you can easily use the IDE to write and run the sample code. The following are some tips on using the IDE and explanations of some IDE behavior that you are likely to see:

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