What are software design patterns and what are their different uses? 

In software engineering, design patterns are proven general solutions to common software design problems that have been identified and documented by experienced software developers. Design patterns are not a finished design that can be directly translated into code. They provide developers with a set of guidelines and best practices to follow when designing software systems.  

Design patterns help implement software design principles such as clean code by providing tools to improve code readability for coders, avoid the expensive acquisition of resources by recycling existing objects and increase the efficiency of the overall development process, with direct support in multiple programming languages.

Design patterns can support developers’ efforts to create software systems that are easier to maintain, extend, and modify over time. However, it’s important to note that design patterns should be used judiciously and only when they are appropriate for the specific problem at hand. 

How many different design patterns are there?

There are at least 26 design patterns discovered to date, but 23 of them are currently the standard in software engineering.

Gang of Four (GoF) design patterns

Although the concept of patterns had been in use for several years, pioneering work in this area started in 1994, when the “Gang of Four” (GoF) authors Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides introduced the concept of design patterns in their book: Design Patterns: Components of Reusable Object-Oriented Software. 

Since the 4 authors are considered the parents and main evangelists of the 23 design patterns, these patterns are frequently referred to as the GoF (Gang of Four) design patterns.

What are the 23 most popular types of design patterns in computer programming and system design?

There are many different design patterns, each with its own specific purpose and implementation details. The most commonly used types of design patterns are divided into 3 categories:

• Creational design patterns
• Structural design patterns
• Behavioral design patterns

Creational design patterns

These patterns focus on the process of object creation, providing ways to create objects in a manner suitable for a particular situation. 
Some examples of well-known creational design patterns include:

1. Abstract  – This pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes.
2. Builder – This pattern allows developers to handle the creation of different types and representations of a rather complex object by using the same creation code.
3. Factory Method  – The Factory Method pattern helps avoid tight coupling between classes by allowing them to defer instantiation of objects to subclasses instead.
4. Prototype  – It allows to copy existing objects without making code dependent on their classes.
5. Singleton  – This type of pattern helps ensure that only one instance of a class exists in memory at any given time by centralizing access across all connected objects.

Structural design patterns

These patterns deal with the composition of classes and objects, providing ways to organize and structure them to form larger systems. 

Some examples of well-known structural design patterns include:

1. Adapter  – This pattern allows to connect two incompatible classes.
2. Bridge  – This pattern makes it possible to isolate the implementation and abstraction parts of a class so that they can change independently.
3. Composite  – This pattern creates hierarchical tree structures used for representing part-whole relationships between objects.
4. Decorator – This pattern allows you to add new functionality to an object or remove an existing one without changing the object’s function or appearance.
5. Façade – This type of pattern is used to provide an easy-to-use unified interface over a set of related but complex classes.
6. Flyweight – This pattern helps reduce the cost of complex object models by storing and creating new objects when similar objects are not found.
7. Proxy – It is useful for protecting a class from too many requests or to provide additional logic/rules when allowing access to an existing class.

Behavioral design patterns

These patterns focus on the communication and interaction between objects, providing ways to define the behavior of objects and how they interact with each other. 

Some examples of well-known behavioral structural design patterns include: 

1. Chain of Responsibility – This pattern is used in software design to achieve loose coupling by passing a client request to a chain of objects to process them.
2. Command – This type of pattern provides a way for clients to send commands without having to know about or tightly coupled with an external receiver interface or data. It allows two unrelated interfaces to work together by using an adapter object which wraps the interface into the one expected by its client class.
3. Interpreter – This pattern provides a way for clients to parse and interpret a language into meaningful instructions used by other programs.
4. Iterator – It helps to access elements of a data structure without exposing the underly details.
5. Mediator – This pattern helps reduce chaotic dependencies between objects, by providing a mediator between objects and assisting in the implementation of loose-coupling between objects.
6. Memento – This pattern allows developers to restore state of an object to a previous state.
7. Observer – It is useful when an object needs to be aware of changes made to the state of another object and act accordingly. An example would be a stock ticker which notifies subscribers each time a stock price change.
8. State – It allows objects to change their behavior based on different states and provides a mechanism for transitioning between said states. This helps as objects adapt faster to environmental changes.
9. Strategy – This pattern helps define a family of algorithms which can be interchangeable gradually based on expectations from clients.
10. Template Method – This pattern allows developers to define an algorithm in its structure and then subclasses can implement the essential details of it. It helps developers avoid code duplication and create reusable code pieces to define the steps of an algorithm.

Why design patterns are important elements in software development?

Design patterns are important because they provide a common language for developers to communicate with each other. They provide a set of solutions to common problems which can be used to ensure that code is written in a consistent manner. They also make it easier for developers to understand code written by others and make debugging and maintenance easier within the development process.

Implementing and reusing application design patterns

To apply a design pattern effectively, you need to identify the problem it is meant to solve first. Patterns are presented as reusable solutions in various books on software engineering. Once the problem is defined, you will need to properly analyze the most suitable solution from existing patterns.  

Once you’ve chosen a pattern that suits your situation, you’ll then need to implement it in code or architecture accordingly. To apply a pattern in code or architecture properly, developers should understand the interaction among different parts of the application. The order of operations must also be considered for successful implementation of pattern.

Criticism on the use of design patterns in code design

Design patterns have been criticized for their lack of rigor and formalism. People argue that design patterns are too abstract and lack a solid foundation in mathematics or software engineering principles. Furthermore, they claim that design patterns do not provide a guarantee of correctness and are often used as a crutch by inexperienced developers.

Where to learn programming design patterns to develop your skills?

There are many resources available for learning design patterns. Here are some options:

Books related to design patterns

There are several books on design patterns that provide a thorough understanding of the concepts and their applications. Some popular titles include “Design Patterns: Elements of Reusable Object-Oriented Software” by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, “Head First Design Patterns” by Eric Freeman and Elisabeth Robson, and “Design Patterns Explained: A New Perspective on Object-Oriented Design” by Alan Shalloway and James R. Trott.  Peter Norvig’s paper “Design Patterns  in Dynamic Languages” is also something worth considering when learning design patterns.

Online courses about software engineering practices

There are many online courses available that cover design patterns. Some popular platforms that offer courses on this topic include Coursera, Udemy, and Pluralsight. These courses can range from free to paid and cover a variety of programming languages. 

Tutorials covering OOP, MVC and other types of design patterns

There are many tutorials available online that provide an introduction to design patterns. These tutorials can be a good starting point for people who are new to the topic. Some popular websites that offer tutorials on design patterns include Tutorials Point, DZone, and CodeProject. 

Related topics such as the fundamental principles of software design, clean code architecture and Domain-Driven Design can also be explored for a deeper dive into software design. 

Simple and easy to use code examples of design pattern implementation

One of the best ways to learn design patterns is by studying code examples. Many open-source projects and code repositories have examples of design patterns in use. You can study these examples to understand how design patterns work in practice. 

Engineering communities

There are many online communities dedicated to software design patterns. These communities can be a great resource for learning about new patterns, asking questions, and discussing best practices. Some popular communities include the design patterns subreddit and the Design Patterns Group on LinkedIn.

Conclusion: Summarizing key points about design patterns

To sum up, design patterns are an effective tool in software engineering, providing coders with a systematic approach towards solving common problems in software development. A variety of design patterns exist and can be used in various situations. For example, developers may use the Factory Method pattern to solve the issue of creating objects without specifying the exact class of the object to be created or the Singleton pattern to ensure only one instance of a class exists in memory at any given time.  

When implementing and reusing design patterns during the development process, coders should identify the problem they are trying to solve first, then choose an appropriate pattern accordingly and apply it in code or architecture accordingly.