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This article mainly explains "how to write Hello World in Java". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn how to write Hello World in Java.

Too many people ask HelloWorld questions, and they often start with "ask the simplest question." In fact, in retrospect, I also came from this stage, saying "Hello" is really the simplest question? ... / / think all right, back to the point, let's say "HelloWorld!" In java...

First of all, let's assume that our platform is Windows+JDK (pretty much the same in Linux). This environment is quite universal, basic and introductory. To make sure that JDK is installed correctly, the next step is to carefully type in the HelloWorld source code on a tutorial, save it, and then compile it, javac. Here's the problem:

* error 1:

'javac' is not an internal or external command, nor is it a runnable program or batch file.

(javac: Command not found)

The reason is that the environment variable path is not set properly. Under Win98, add path=%path%;c:jdk1.2bin,Win2000 to autoexce.bat, then Control Panel-> system-> Advanced-> Environment variable-> system variable. Saw it? Double-click Path and add c:jdk1.2bin at the end. Of course, we assume that JDK is installed in the c:jdk1.2 directory (a bit of a monk? ). It seems that it will take a restart of the system to work. (/ / got it! / / Tomato) OK, try again! Javac HelloWorld .

* error 2:

HelloWorld is an invalid option or argument.

Come on, be professional. Java's source code must be saved as a .java file, and it must be compiled with full .java.

OK, javac HelloWorld.java (it must be done this time, right? )

* error 3:

HelloWorld.java:1: Public class helloworld must be defined in a file called

"HelloWorld.java".

Public class helloworld {

^

This problem is because the name of your class does not match the name of the file. (who said that, obviously see that other people have written () OK, to be exact, a Java source program can define multiple classes, but there can only be one class with the public attribute, and it should be consistent with the file name. Also, the main method must be placed in the class of this public in order to java (run) the class. Another point is that the Java language is strictly case-sensitive, beginners should pay attention to it. As in the example above, helloworld and HelloWorld are considered to be different, so. Oh... Okay, it's done. Hee hee. Javac HelloWorld.java... (why, why is there nothing there? ) / / faint this is the compilation passed! See if there is an extra HelloWorld.class (hehe..). As taught in the book:) java HelloWorld (!! I know that, not java HelloWorld.class)

* error 4:

Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld

Oh, this is the famous classpath problem. In fact, classpath is a concept in Java that is involved in the compilation process. Classpath is to indicate where to find the classes you need. It's as simple as that. Since our HelloWorld doesn't use other classes (not in the java.lang package), we don't encounter this problem at compile time. At run time, it's time to indicate where your class is. The solution can be run with the following command:

Java-classpath. HelloWorld "." Represents the current directory. Of course it's a little troublesome to do so (it's too troublesome! We can set the default classpath in the environment variable The method is just like setting path above. Set classpath to:

The following two suggestions of classpath=.;c:jdk1.2libdt.jar;c:jdk1.2libtools.jar are also set up.

It will be useful for future development. Java-classpath. HelloWorld (if you don't come out, I won't learn java)

* error 5:

Exception in thread "main" java.lang.NoSuchMethodError: main

(/ / bang) No, hold on. Look at your code. The problem lies in the definition of the main method. Is it written in the right place?

Is it written like this:

Public static void main (String args []) {/ / not a word, don't ask why.

Yes, including upper and lower case!

Java-classpath. HelloWorld (resigned to fate! )

Hello World!

(faint! Finally.)

Welcome to the Java world! So being unable to run HelloWorld is really not the "simplest problem".

Attached: HelloWorld.java

/ / HelloWorld.java

Public class HelloWorld

{

Public static void main (String args [])

{

System.out.println ("Hello World!")

}

}

At this point, I believe you have a deeper understanding of "Java how to write Hello World". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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