Head First Design Patterns

OO Basics

• Encapsulates what varies.
• Favour composition over inheritances.
• Program to an interfaces, not implementations

OO Principles

• Encapsulates what varies.
• Favour composition over inheritances.
• Program to an interfaces, not implementations
• Strive for loosely coupled designs between objects that interact.
• Classes should be open for extension, but closed for modification.
• Depend on abstractions. Do not depend on concrete classes.

Design Patterns

Strategy Pattern

The strategy patterns defines a family of algorithms, encapsulates each one and makes them interchangeable.
Strategy lets the algorithm vary independently from clients that use it.

Obverver Pattern

The observer pattern defines a one-to-many dependency between objects so taht when one object change state, all its dependents are notified and updated.

Decorator Pattern

The decorator pattern attaches additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

Factory Patterns

Factory Method Pattern

The factory method pattern defines an inteface for creating an object, but let subclasses decide which class to instantiate. Factory method lets a class defer instantiation to the subclasses.

Abstract Factory Pattern

The abstract factory pattern provides an interface for creating families of related or dependent objects without specifiying their concrete classes.

Singleton Pattern

The singleton pattern ensures a class only has one instance and provide a global point of access to it.