General CS concepts

This is a post for general CS concepts. To make it easy to link to, i've posted each different concept under their own post. The emphasis will be on OOP (object oriented programming), and examples will either be in Java or some java-pseudo code. At the bottom of each section, i've put some simple questions that should test your understanding of the topic. Try to see how many you can get right. The answers are below them (in a slightly hidden color), just highlight the text to read the answer.

note: Please try to keep comments in this thread to a minimum, pm me about any changes you think should be made. This way the thread will be easier to navigate through. If you have a complete topic you want to add, feel free to post it I'll try to stay on top of this post and put any topics you add into the topics list in this post.

Topics in bold are done (and you can click on the link) Feel free to add on. Also, I've arranged these topics here in alphabetical order, but the posts below aren't because I don't know how to do that, and don't want to break any links...
Topics:
* Abstract Data Types
* Abstraction
* Algorithm Analysis
* Encapsulation
* Exceptions
* Inheritance
* Interfaces
* Methods (functions)
* Passing by Value or Reference?
* Polymorphism
* Recursion
* Static vs. Instanced
* Variables and Objects