What is the content of the $CLASSPATH variable in El Capitan? I installed OS X El Capitan and, along with it, Oracle's Java 8 SDK.
I've already verified that, using java -version, java is correctly installed.
I need to add some user classes to the file path, but, when I use echo $CLASSPATH, I cannot see the actual path being used by OS X. 
How can I know where should I install my user classes?
First, I found out that my Yosemite Installation has also no CLASSPATH set.
Second, when issueing

$ java -help


it directed me to the URL:

Java SE documentation

Klicking there led me to How Java Runtime finds classes and within there it is written:


  "[…] User classes are classes that are defined by developers and third parties and that do not take advantage of the extension mechanism. You identify the location of these classes with the -classpath option on the command line (preferred) or with the CLASSPATH environment variable. See Setting the Class Path.[…]"


Effectively it says "put your classes wherever you want and just run java -classpath &lt;userclassdirectory&gt;. 

Just take time to read the complete document.