a TestClass.java + TestClass.class in the same path.
You cannot just place .class files anywhere. When the CF server starts, it only checks specific locations for classes/jars. Those locations are referred to as the "CF class path". Your compiled .class file must be placed within the CF class path, or it will not be detected.
To use a custom java class:
- Create a source file ie 
YourTestClass.java 
- Compile the source code into a class file ie 
YourTestClass.class 
Place the compiled .class file somewhere within the CF classpath, such as:
WEB-INF\classes - for individual .class files 
WEB-INF\lib - for .jar files (multiple classes)
 
Note: You could also add the item to the CF class path via the ColdFusion Administrator. However, placing the class in one of the default directories is simpler.
 
Restart the ColdFusion server so it detects the new classes
 
Note: Though you can use individual .class files, it is more common to package them into .jar files.