Lesson 1

Welcome to GOF Patterns which is the acroynm for Gang of Four Patterns. The first module in this course presents you with the groundwork in preparation for the material that you will be reading.

• Course Goals:
  In this course you will learn what the GOF (Gang of Four) patterns are and how they help solve common problems encountered in object-oriented design. After completing this course, you will be able to:
  1. Use creational patterns to create objects when constructors will not serve your purpose.
  2. Behavioral patterns characterize the ways in which classes or objects interact and distribute responsibility.You will learn how to use behavioral patterns to reduce complicated flow control.
  3. Furthermore, you will use behavioral patterns to encapsulate algorithms and dynamically select them at run time.
  4. Structural patterns deal with the composition of classes or objects.
  5. The 2 most common techniques for reusing functionality in object-oriented systems are
     
     1. Class Inheritance and
     2. Object Composition
  6. You will learn how to use the Gang of Four Pattners (Design Patterns) to replace inheritance^[1] with composition.^[2]

In the ever-evolving realm of software development, there remains an eternal truism: a developer's proficiency is not just rooted in their foundational understanding of algorithms or languages, but equally in their ability to identify and implement design patterns. This argument extends beyond the technicalities of software construction and touches upon the profound emotional and intellectual essence of a software developer. Here are four compelling reasons, steeped in both emotion and academic rigor, for why every software developer should embrace the study of design patterns:

1. Intellectual Elevation and Empowerment: At the core of our human essence is the need for growth and intellectual fulfillment. Delving into design patterns is akin to equipping oneself with the philosophical frameworks of software engineering. It allows a developer to see beyond mere lines of code and appreciate the deeper, intricate symphony of structured thinking that stands as the bedrock of efficient software solutions. It is an academic pursuit that is both invigorating and empowering, bringing with it an expansive vision of what software development truly is.
2. Alleviating the Emotional Weight of Complexity: Every developer has, at some point, felt the crushing weight of a convoluted codebase or the anxiety of introducing a change that could ripple chaos across modules. Design patterns emerge as a beacon of hope in such tumultuous terrains. They offer standardized solutions that slice through the morass of complexity, bringing clarity and tranquility to the developer's mind. By embracing these patterns, a developer not only imbues their code with structural elegance but also soothes their own emotional journey in the software development process.
3. The Joy of Collaborative Resonance: Collaboration is not merely about understanding one's own code but being able to resonate emotionally and intellectually with one's peers. Design patterns, being shared vocabularies of solutions, allow for this profound connection. When developers are aligned in their knowledge of patterns, they share an unspoken bond, a silent language that facilitates smoother collaboration. The resultant cohesion is not just about efficient teamwork; it's about shared joy, mutual respect, and a harmonized vision.
4. Legacy and the Desire to Transcend Time: In the heart of every developer lies the yearning to create something timeless, to leave an indelible mark on projects and teams. Design patterns are the bridges to this legacy. By embedding these patterns into software, developers ensure that their contributions are resilient, maintainable, and scalable. It's a testament to their craftsmanship and an ode to their desire to be remembered, to have their work stand the test of time and be a source of inspiration for generations of developers to come.

In conclusion, design patterns are more than mere technical tools; they are emotional compasses and intellectual lighthouses that guide developers in their journeys. Embracing them is to embrace growth, serenity, connection, and legacy. It is a commitment to oneself, to one's craft, and to the broader community of software artisans.

The pattern name is a reference we can use to describe a design problem, its solutions, and consequences. Naming a pattern immediately increases our design vocabulary and lets us design at a higher level of abstraction. Having a vocabulary for patterns allows us to talk about these patterns with our co-workers and to ourselves. It makes it easier to think about designs and to communicate them and their trade-offs to others.
The problem describes when to apply the pattern and explains the problem and its context. It might describe specific design problems such as how to represent algorithms as objects. It might describe class or object structures that are associated with an inflexible design. Sometimes the problem will include a list of conditions that must be met before it makes sense to apply the pattern. The solution describes the elements that make up the design, their relationships, responsibilities, and collaborations. The solution doesn't describe a particular concrete design or implementation, because a pattern is like a template that can be applied to many different situations. Instead, the pattern provides an abstract description of a design problem and how a general arrangement of elements solves the design problem.

A design pattern is a general reusable solution to a commonly occurring problem within a given context which implies the following. Programmers often encounter the same problem repeatedly and use a best practice type that has been documented and proven to work. A design pattern represents an idea, and we should write an implementation for that pattern and implement that in our code.
Advantages of Design Patterns
Using a design pattern has a few advantages. We get to use a solution that is known to work. The tradeoffs are well documented, so we do not stumble over problems that have already been solved. Furthermore, design patterns also serve as communication aids. Your project manager can say, "We will use a singleton,"" and that one word is enough to tell you what is expected. When books or web pages document patterns, they do so using a consistent format. We observe this universal format by including sections for the

1. Problem,
2. Solution, and
3. Benefits

of the singleton pattern. The problem section explains why we need the pattern, what problem we are trying to solve. The Solution section explains how to implement the pattern. The Benefits section reviews why we need the pattern and how it has helped us solve the problem. Some of the benefits are hinted at in the Problem section.

[1] inheritance: The concept of classes automatically containing the variables and methods defined in their supertypes.

[2] composition: Creating objects with other objects as members. Composition should be used when a has-relationship applies