Computer Science:

    https://www.codecademy.com/  -  a good start for learning the basics of Java.  Will teach you the basics for free, need to buy Pro account to use any of the projects. (personally, I don't think the pro account is worth it)


    www.javabat.com  -  A wide variety of quick coding exercises, may be used in class.


    Https://repl.it/  -  Online repository for programming problems (also has a working online IDE).  Many past AP questions have been translated into repl.it as problems


    http://www.khanacademy.org/  -  online tutorials for just about anything