More than two decades since design patterns have appeared, many developers consider them the most important discovery in software development. Others still find them a bad idea. And both are right! How comes?

In this course, you will learn how design patterns can be applied to make code better: flexible, short, readable. Flexibility is the key element in design patterns. You will learn how to decide when and which pattern to apply by formally analyzing the need to flex around specific axis. You will learn which pattern is adding which kind of flexibility, and what are the most common forms of implementation in practice. You will also learn common pitfalls and ways to overcome them when applying specific patterns.

Through a series of demonstrations, you will learn one design pattern at a time. In each demonstration, we shall start from an existing implementation which faces difficulties to accommodate the next requirement proposed by the customer. That will invariantly trigger a series of designing attempts, some doomed to fail, others having prospect to succeed. But what will learn in this course, is that each successful design will exhibit one kind of flexibility, which will be of critical importance to support the troublesome request posed by the customer. It will come as no surprise to you to learn that each such special kind of flexibility will be one specific design pattern.