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Chapter 7 Object oriented design

OOP questions are about demonstrating that you understand how to create elegant, maintainable object-oriented code.

Handle ambiguity: many questions are intentionally vague, so that you ask questions. Who's going to use it, how.
Define the core objects: if it's a restaurant, the core objects might be table, guest, party, etc.
Analyze relationships between the objects. Which objects are member of other objects, which inherit from which, are relationships many-to-many or one-to-many? Party should have an array of guests, server and host inherit from employee, etc.
Investigate actions: what will objects do

Design patterns

Singleton class

This pattern ensures that a class has only one instance and ensures access to the instant through the application, it can be useful where you have a global object with exactly one instance. We might want to implement Restaurant with exactly one instance of Restaurant. Many people dislike this pattern, because it can interfere with unit testing.

public class Restaurant {
    private static Restaurant _instance = null;
    protected Restaurant() {...}
    public static Restaurant getInstance() {
        if (_instance == null) {
            _instance = new Restaurant();
        }
        return _instance;
    }
}

Factory method

It offers an interface for creating an instance of a class, with its subclasses deciding which class to instantiate.

public class CardGame {
    public static CardGame createCardGame (GameType type) {
        if (type == Gametype.Poker) {
            return new PokerGame();
        } else if (type == Gametype.BlackJack) {
            return new BlackJackGame();
        }
        return null;
    }
}

Resouces

C++ solutions

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