Not setting the classpath correctly leads a lot of frustration that can be easily avoided.

To include a .jar library in a classpath, you have to include the specific filename too. You cannot just include the directory that contains the .jar.

It is advisable to have '.', that is, the current directory in the classpath too.

Every time you change the classpath, you must open a new terminal (or command window) for the changes to take effect.

For Linux systems: my personal .bash_profile file. Every time I want to change the classpath, I edit the classpath variable in it, and run $. ~/.bash_profile for the changes to take effect. Remember the changes take place only in the shell or command window in which it was run.