The CLASSPATH is an environment variable that tells the Java compiler javac.exe where to look for class files to import or java.exe where to find class files to interpret. 

In contrast, the PATH is an environment variable that tells the command processor the where to look for executable files, e.g. *.exe, *.com and *.bat files. The Classpath is one of the most confusing things in Java. Unfortunately, you must master it to even compile HelloWorld. 

CLASSPATH And File Naming Recipes

Here are my simplified rules for using CLASSPATH and naming the files on the javac.exe and java.exe command line: 

1. Put every class in a package. Don't use the default package. 

2. Use the latest JDK. It will be the one everyone you ask help from is familiar with. Two dangling prepositions in one sentence. Churchill would be proud. 

3. Configure your SET CLASSPATH= in the environment to clear it out. 

4. You don't need to explicitly include rt.jar: