Could not find main class HelloWorld

Question

I installed Java 1.7.0 in the following folder C:\Program Files\Java. My operating system is Windows XP(Version 2002) with Service pack 3.

The environment variables which I set are:

• CLASSPATH : C:\Program Files\Java\jdk1.7.0\jre\lib\rt.jar;

• Path : C:\Program Files\Java\jdk1.7.0\bin;

• JAVA_HOME : C:\Program Files\Java;

I have presented here the class names which are in my system.

Next I wrote a program, HelloWorld.java:

import java.io.*;  class HelloWorld {     public static void main(String[] args)      {         System.out.println("Hello World!");     } } 

When I am compiling using javac HelloWorld.java it is compiling fine.

But after I issue java HelloWorld I am encountering the below error:

Error: Could not find main class HelloWorld Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld         at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:198)  Caused by: java.lang.ClassNotFoundException: HelloWorld         at java.net.URLClassLoader$1.run(URLClassLoader.java:299)         at java.net.URLClassLoader$1.run(URLClassLoader.java:288)         at java.security.AccessController.doPrivileged(Native Method)         at java.net.URLClassLoader.findClass(URLClassLoader.java:287)         at java.lang.ClassLoader.loadClass(ClassLoader.java:422)         at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:325)         at java.lang.ClassLoader.loadClass(ClassLoader.java:355)         at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:195) 

After a bit of searching around, I found that may be something wrong in the environment variable. I tried to play with that but no luck.

I even RESTARTED the machine and then again I tried to run but with same fate.

Answer 1

Tell it where to look for you class: it's in ".", which is the current directory:

java -classpath . HelloWorld 

No need to set JAVA_HOME or CLASSPATH in this case

Answer 2

You are not setting a classpath that includes your compiled class! java can't find any classes if you don't tell it where to look.

java -cp [compiler outpur dir] HelloWorld 

Incidentally you do not need to set CLASSPATH the way you have done.