20 Questions
In the game 20 questions one player thinks of something and the other players ask yes or no questions in an attempt to determine what the first player is thinking of. The first player considers each question in light of his privately held information and replies with the appropriate response. This is a great model for encapsulation. The first player thinks of an object and holds it in memory, and the details of the object are not available to the other players (private state). Other player ask questions (invoke behaviors) to gather information about the object. The behaviors are limited to yes or no questions and consist mostly of a common, predictable set of useful questions: Is it an animal, vegetable, or mineral? Is it bigger or smaller than a breadbox? Is it something you eat? etc. Suppose the game ends without a successful guess, and the first player thinks of another object for the next round of questions. The new object replaces the previous one in his mind, and the