Package and CLASSPATH

Question

Hi,
I have a hard time understanding the package and CLASSPATH. I want to have a solid understanding of it. I read some tutorials online but didn't make me fully understand. How does declaring a package effect the CLASSPATH? Say I have following:
(This is from one of the tutorial- http://home.cogeco.ca/~ve3ll/jatutor4.htm)
C:\myclasses\world\moon\HelloMoon.java
C:\myclasses\world\HelloWorld.java
HelloMoon.java is defined as
package world.moon;
public class HelloMoon {
private String holeName = "rabbit hole";
public String getHoleName() {
return holeName;
public void setHole(String holeName) {
this.holeName = holeName;
public static void main(String[] args){
     HelloMoon moon = new HelloMoon();
     System.out.println(moon.getHoleName());
HelloWorld is defined as
package world;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
if the CLASSPATH is set : set CLASSPATH=.;C:\myclasses;
Once the CLASSPATH has been set (and compiled .java file); it can be called using the following from any path of directory:
java world.HelloWorld
java world.moon.HelloMoon
But it does not explain the details why it works this way. Also, if I want to run it without using "world" prefix to run HelloWorld, what do I need to set up?
also for the HelloMoon?
When I tried running those classes by going to an appropriate directory, I got the noClassDefFound (using command like "java HelloWorld" or java "HelloMoon").
Thanks in advance...

Answer 1

[Javapedia: Classpath|http://wiki.java.net/bin/view/Javapedia/ClassPath]
[How Classes are Found|http://java.sun.com/j2se/1.5.0/docs/tooldocs/findingclasses.html]
[Setting the class path (Windows)|http://java.sun.com/j2se/1.5.0/docs/tooldocs/windows/classpath.html]
[Setting the class path (Solaris/Linux)|http://java.sun.com/j2se/1.5.0/docs/tooldocs/solaris/classpath.html]
[Understanding the Java ClassLoader|http://www-106.ibm.com/developerworks/edu/j-dw-javaclass-i.html]
java -cp .;<any other directories or jars> YourClassNameYou get a NoClassDefFoundError message because the JVM (Java Virtual Machine) can't find your class. The way to remedy this is to ensure that your class is included in the classpath. The example assumes that you are in the same directory as the class you're trying to run.
javac -classpath .;<any additional jar files or directories> YourClassName.javaYou get a "cannot resolve symbol" message because the compiler can't find your class. The way to remedy this is to ensure that your class is included in the classpath. The example assumes that you are in the same directory as the class you're trying to run.