Java Hello World程序

桃扇骨 2023-02-28 06:11 2阅读 0赞

Whenever we start to learn a programming language, the first program is always to print the Hello World. In the last article, we learned [how to install Java on Windows 10][]. Now we are ready to write and run our first Hello World Java program.

每当我们开始学习编程语言时，第一个程序始终是打印Hello World。 在上一篇文章中，我们学习了[如何在Windows 10上安装Java][how to install Java on Windows 10] 。 现在，我们准备编写并运行我们的第一个Hello World Java程序。

## Java Hello World程序 **(****Java Hello World Program****)** ##

To keep things simple and working for a new user, here is the sample hello world program that you can use.

为了使事情变得简单并为新用户工作，这里是您可以使用的示例hello world程序。

public class JavaHelloWorldProgram {
    
    	public static void main(String args[]){
    		System.out.println("Hello World");
    	}
    }

Save above program as `JavaHelloWorldProgram.java` in any directory.

将以上程序另存为`JavaHelloWorldProgram.java` 。

### 1.编译并运行Java Hello World程序 **(****1. Compile and Run Java Hello World Program****)** ###

Open Command Prompt and go to the directory where the hello world program file is saved. Then execute the below commands in order.

打开命令提示符，然后转到保存hello world程序文件的目录。 然后依次执行以下命令。

$javac JavaHelloWorldProgram.java
    
    $java JavaHelloWorldProgram
    Hello World

[Java 11][] or higher, then you can simply execute [Java 11][]或更高版本，则只需执行 `java JavaHelloWorldProgram.java` and it will compile and execute the program for you. No need to explicitly compile and then run the java program. `java JavaHelloWorldProgram.java` ，它将为您编译并执行程序。 无需显式编译然后运行Java程序。

### 2. Java程序要点 **(****2. Java Program important points****)** ###

1.  A Java source file can have multiple classes but only one public class is allowed.
    
    一个Java源文件可以有多个类，但只允许一个公共类。
2.  The java source file name should be same as the public class name. That’s why the file name of our program is `JavaHelloWorldProgram.java`
    
    Java源文件名应与公共类名相同。 这就是我们程序的文件名为`JavaHelloWorldProgram.java`
3.  When we compile the code, it generates byte code and save it as `Class_Name.class` extension. If you look at the directory where we compiled the java file, you will notice a new file created `JavaHelloWorldProgram.class`
    
    当我们编译代码时，它将生成字节代码并将其另存为`Class_Name.class`扩展名。 如果查看我们编译Java文件的目录，您会注意到创建了`JavaHelloWorldProgram.class`的新文件
4.  When we execute the class file, we don’t need to provide complete file name. We need to use only the public class name.
    
    当我们执行类文件时，我们不需要提供完整的文件名。 我们只需要使用公共类名。
5.  When we run the program using java command, it loads the class into [JVM][] and looks for the [main method][] in the class and runs it. The main function syntax should be same as specified in the program, else it won’t run and throw exception as `Exception in thread "main" java.lang.NoSuchMethodError: main`.
    
    当我们使用java命令运行程序时，它将类加载到[JVM中][JVM]并在类中查找[main方法][main method]并运行它。 主要函数语法应与程序中指定的语法相同，否则它将不会运行并引发异常，因为`Exception in thread "main" java.lang.NoSuchMethodError: main` 。

I have recently created a short video for Java Hello World Program using Notepad and then Eclipse. Watch it for a better understanding.

我最近使用记事本和Eclipse为Java Hello World程序创建了一个简短的视频。 观看它以获得更好的理解。

[演示地址][Link 1]

That’s all for this post and you can start playing with your first class. In the next post, I will get into further details of classes, JDK, JVM, and other features provided by the Java programming language.

这就是这篇文章的全部内容，您可以开始上一堂课。 在下一篇文章中，我将进一步探讨类，JDK，JVM和Java编程语言提供的其他功能的详细信息。

Update: Read this post to know about [JDK vs JRE vs JVM][] in java.

更新：阅读这篇文章，以了解[Java中的JDK，JRE和JVM][JDK vs JRE vs JVM] 。

> 翻译自: [https://www.journaldev.com/481/java-hello-world-program][https_www.journaldev.com_481_java-hello-world-program]

[how to install Java on Windows 10]: https://www.journaldev.com/476/java-windows-10-download-install
[Java 11]: https://www.journaldev.com/24601/java-11-features
[JVM]: https://www.journaldev.com/2856/java-jvm-memory-model-memory-management-in-java
[main method]: https://www.journaldev.com/12552/public-static-void-main-string-args-java-main-method
[Link 1]: https://www.youtube.com/embed/ZREpFyjTDho?feature=oembed
[JDK vs JRE vs JVM]: https://www.journaldev.com/546/difference-jdk-vs-jre-vs-jvm
[https_www.journaldev.com_481_java-hello-world-program]: https://www.journaldev.com/481/java-hello-world-program