About Java, SOS! ! !

please refer to the following steps for configuration, try to see if HelloWord can run normally, and then run your. exe, which should be no problem.

first, you configure the environment according to the following, and then go to the file directory when running. For example, if your hello.java is on disk D, go to the bottom of disk D first, and then javac hello.java Java Hello. That's it.

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JDK installation setting environment variables

1. Preface

JDK(java Development Kit). It is a set of APIs, or some java Class. The latest version that has been officially released is JDK1.3. Considering that I am not familiar with linux, and most of them are under MS system, I use win2 here.

second, download and install

The download address is the official JAVA website: java.sun.com, which is also everywhere in China.

under p>Windows, run the. exe file directly and install it in a directory. I use F:\jdk13 as an example here.

III. Configure

Select "My Computer" on the desktop (right click)

Advanced

Environment variables

In "System variables"-> "new"

enter: CLASSPATH in the variable name and:

F:\JDK13\LIB\dt.JAR in the variable value; F:\JDK13\LIB\TOOLS.JAR; F:\JDK13\BIN; Then determine;

well, after configuration, the environment variables will not be effective until the computer is restarted.

fourth, test

(1) write a simple java program with a text editor:

public class hello world {

public static void main (string args []) {

system. out.println ("hello world!") );

}

}

This example is the famous "Hello World", and its function is to display "Hello World".

note: the file name must be "HelloWorld.java" and it is case-sensitive. Careful friends will notice that it is the same as the name after public class.

(2) compile: execute at dos command prompt: (note case)

javac HelloWorld.java

if it is normal, the HelloWorld.class file will be generated.

(3) Run: execute at the dos command prompt: (pay attention to case)

java HelloWorld

Here is a problem that beginners of java are likely to encounter (I am not afraid of jokes, so am I), that is, input:

java HelloWorld.class

There is more. class behind it, so be sure to pay attention. Otherwise, the following error will appear:

exception in thread "main" java.lang.noclassDefoundError: Hello World/class

(I guess, did java translate "."with "/"or for other reasons I don't know)

Well, there should be a great "hello" when running java HelloWorld.

at this point, you have successfully configured the JDK, and you can start a long and painful java process (for friends like me who didn't know Java before, it can be described as "pain", unfamiliar concepts, unfamiliar java api ..., but don't worry, I will get started and improve slowly with you ...).