Introduction to Design Patterns

This book has been written to teach the reader how to use Design Patterns in a clear and simple way with a practical approach based on real-world scenarios.

This is not a conventional book about Design Patterns, mainly because it doesn't follow the same structure you can find on essential written works related to this subject. Instead, I chose to offer a real-world perspective in which the reader could learn how to use Design Patterns in real environments and apply them to real projects.

When I started studying Design Patterns, I found out that the examples were always based on irrational scenarios which you may never find, like drawing geometrical shapes, making a pizza, or creating a series of animal classes that bark or meow; those examples I always ran into, even though they did explain the concept, were very difficult to be translated into real-world scenarios.

In this book I try to go beyond those typical examples to do truly incredible things, such as:

• Creating your own language to make SQL queries over an Excel file.
  
• Creating applications that can change between more than one database, like Oracle and MySQL, based on the needs of the user.
  
• Managing global settings of your application.
  
• Creating an execution pool to manage the number of threads that are running simultaneously, keeping your application from running out of resources.
  
• Using proxies to manage the security of your application.
  
• Using strategies to change the manner in which the users are logged into your application; it could be via database, web service, etc.
  
• Creating your own state machine to manage the life-cycle of your server.
  

These are just a few of the 25 examples that will be covered in this book, each of them including their source code, which you can download, run and analyze on your own computer. Lastly, I'll cover UML examples and essential concepts from Object-Oriented Programming, like Inheritance, Polymorphism, Encapsulation, Abstraction, Cohesion and Coupling; which you can find on sections A and B of this book.