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Operating Systems Linux running java program question
# 1  
Old 04-09-2009
running java program question
hi, i have just written a simple hello world java program in my linux server, installed jdk ... and tried to compile and run it and it gave me some errors.

please details below:

Code:
[root@localhost javaFiles]# cat HelloWorld.java
import java.util.*;
import java.io.*;

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

#javac HelloWorld.java
#
[root@localhost javaFiles]# ls
HelloWorld.class  HelloWorld.java

[root@localhost javaFiles]# java HelloWorld.java
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld/java
Caused by: java.lang.ClassNotFoundException: HelloWorld.java
        at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:336)

would someone please tell me what is wrong? thanks very much.

Edit: Added code tags. Please use them.
Last edited by Neo; 04-09-2009 at 05:20 PM.. Reason: please use code tags
# 2  
Old 04-09-2009
Looks like you need to set your Java environment variables correctly, for example Jave CLASSPATH.

See this reference:

Classpath (Java) - Wikipedia, the free encyclopedia
# 3  
Old 04-09-2009
thanks, i think that is the problem. do you know which path i should set it to? i know i am supposed the one to know this answer.

i meant, what file (some kind of jar file? ) am i supposed to find in the path that i should set to my java CLASSPATH?

sorry, i am pretty green to the whole thing. i was trying to ask how do i find out which path i should set? i use "yum install jdk* " to download and install my jdk.
# 4  
Old 04-09-2009
You have to set CLASSPATH to the home directory of your Java installation.
# 5  
Old 04-13-2009
Code:
[root@localhost javaFiles]# cat HelloWorld.java
import java.util.*;
import java.io.*;

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

#javac HelloWorld.java
#
[root@localhost javaFiles]# ls
HelloWorld.class  HelloWorld.java

[root@localhost javaFiles]# java HelloWorld.java
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld/java
Caused by: java.lang.ClassNotFoundException: HelloWorld.java
        at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:336)

Actually, the problem is having a wrong command, not classpath issue.

It should read

Code:
java HelloWorld

without the extension. The "dot" is considered a namespace separator so Java runtime will look for a file HelloWorld/java.class in the current directory and of course it does not exist.
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