I am anti-Eclipse just because, so I like to add .jar file manually.

  1. Create ~/.dev directory
  2. Add the jar file (in my case, junit-4.11.jar) you want to include in ~/.dev.
  3. In ~/.bash_profile, add export CLASSPATH=$CLASSPATH:~/.dev/junit-4.11.jar
  4. Close the current terminal and open a new terminal.

My system is Mac OS X Mavericks version 10.9.1.