What are Design Patterns?
What is a Pattern?
Patterns exist everywhere in the world. In culinary, art, medicine, law, mathematics, music, dancing and the list goes on. Genrally, a pattern is identified as a recurring arrangement created to solve some generalized problem. It is simply a solution outline. That solution outline can be used over and over again when registered as a viable option to a repeatable problem. In more formal words, a pattern is a generalized outline of a reusable solution to a recurring problem.
Why Design Patterns?
Have you ever came across situations where the same problem occurs at multiple times while you are coding? A lot of developers around the world face the same problem in daily coding struggle. Equally, there are many solutions out there to identify general iterative problems in development and designing software systems. Design Patterns are the most popular and standard solutions for those recurring problems.
Who Invented the Concept?
Even though billions of people use the idea to solve many problems across the world, a person has defined, encapsulated best practices and found a global standard for design patterns. Christopher Alexander from Austria is a building architect and a civil engineer. He came up with creative solutions to recurring construction issues where building engineers are obsessed with. Which was published as A Pattern Language: Towns, Buildings, Construction (Oxford University Press, 1977) which provides patterns for architecting successful buildings and towns.
Alexander’s definition of the Pattern,
Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice.
This is the central idea where software scientists were getting inspired to invent software design patterns.
What is GOF?
GOF stands for Gang of Four, in the software field, they are the super heroes who invented the precious concept of design patterns. If not, designers and developers are still wondering here and there wasting time and effort to find various solutions to recurring problems. The gang is Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides. The final deliverables are encapsulated and finely documented into the book Design Patterns: Elements of Reusable Object-Oriented Software which is supported by Addison-Wesley in 1995
What is a Software Design Pattern?
Software design pattern is a known, formal way to solve common coding difficulties. In more formal words, it is an identified and proven solution template to a recurring problem in a particular software context. Most of the software design pattern and well defined and pre-evaluated. In software designing real world, the components are identified as objects oriented terms. Hence, most of the design patterns are illustrated via class, object, interface relationships and their inter-communication behaviors.
The most important thing to remember is these design patterns are not finalized solutions which can be transformed directly into the code. Those are just templates or outlines for resolving problems. That template can be utilized in various situations in designing and implementing software systems. It is simply a proposed generalized solution to consume in an ad-hoc manner using our code samples.
In Object Oriented Style
Design patterns are based on object oriented concepts, hence it’s easier to use with languages which based on OOP. Different OOP languages possess different mechanisms to apply patterns. In object oriented terms, like a class is a blueprint of an object and object provides the actual implementation, a design pattern is the blueprint represent the conceptual design while actual implementation will be the instance of that design pattern, which is customized to individual usage.
Why are Design Patterns essential in Software Design?
Design patterns are essential when designing complex systems. Engineers and architects rely heavily on design patterns when the problem domain is getting serious. The most complex and profound anomalies can be addressed via identified design patterns without wasting valuable time. Let’s learn why everybody likes design patterns this much,
- Provide a solution template for a pre-identified, time-consuming and recurring problem. Since the problem was analyzed thoroughly and solutions are applied successfully, people who use that pattern need not worry about unexpected and inaccurate results. Simply, there is no re-inventing the wheel part for the defined design patterns.
- Help to design and implement new systems without spending a long time and resourcefully.
- Ability to extend and modify the codes without much difficulty which improves the maintainability of the system
- Well documented common terminology for every pattern makes it easy to refer at any point. It will make any discussions and analysis easier which also improves the individual and team learning.
Main Components of a Design Pattern
Likewise, every concept or idea, design pattern also made up of the main set of components to clearly define its usage and existence in the software world. A design pattern is a predefined template which is formed using four main building blocks. These building blocks could be represented as the elements of the proposed template. Following four elements gather to create a meaningful design pattern to solve a recurring software problem.
Every documented design pattern has a name. The pattern name act as the identifier for the design pattern. This typically denotes the design problem and solution in short terms, and it helps the ability of easy reference within the community providing a common vocabulary for software professionals.
This is the part which addresses the nature of the design problem and its applicability. The regarding pattern could be valid in any situation where the identified and generalized problem occurs. It helps to derive when to apply the pattern by describing the problem and its context. The problem might include a set of conditions to meet before applying the pattern in certain scenarios.
This is the part which describes the answer to the design problem. This is not the complete code snippet, but a template with guidelines to apply codes from our context. The solution includes the individual elements that generate the design, the relationships of each element, responsibilities, and collaboration to derive the solution. Hence, all those elements work together to solve the design problem.
This is the component which focuses on result and tradeoffs of the applied design pattern. There could be various types of results when applying a design pattern like system’s flexibility, extensibility, and portability. Most concerning consequences would be space and time trade-offs. These consequences are essential in evaluating design alternatives and figuring out the cost and benefits of pattern application. This feature enables the space to compare the design patterns to analyze a different better solution for the actual problem.
Elements which form a Design Pattern Template
Since a design pattern is a solution template for a recurring problem, that template should have the basic elements to build itself. These set of elements forms a format for the pattern template. The template creates a uniform structure for the proposed solution enabling easy learning, comparison, and usage of a pattern. Together, following elements will generate a viable solution for your design problem.
|Name||Give an identity to the pattern|
|Intent/Purpose||What does the design pattern do or what is the design issue it will address|
|Context||The general situation which the pattern to be applied|
|Forces||The issues or concerns to consider when applying the pattern|
|Solution||The recommended method to solve the problem in the given context|
|Consequences||What are the results and trade-offs of applying the pattern and space to adjust independently|
|Implementation||What techniques, rules and language concerns to consider when coding the pattern|
|Related Patterns||A list of related or similar patterns|
|Sample Code||Code snippet to get the idea of the implementation|
|Known Uses||Examples of the patterns in real system|
Real world example,
Problem: You love to have one chocolate sauce with almost all of your milk and cream related desserts
Context: When you are at your home or having a picnic
Forces: You can’t make it from the scratch whenever a dessert shows up
Solution: Make a large jar of chocolate sauce and keep it refrigerated to use when needed
Consequences: Chocolate sauce may expire after 3 – 4 months
Types of Design Patterns
Design patterns are reusable solutions to common problems that occur in software design. They provide a template for solving a particular problem that can be adapted to suit different situations. Design patterns can be classified into three main types: Creational, Structural, and Behavioral patterns. This article will discuss each type of design pattern, their purpose, and some examples.
Creational Design Patterns
Creational design patterns are concerned with the process of object creation. They help to abstract the instantiation process, making it easier to manage and maintain the code. Some common creational design patterns include:
1. Singleton Pattern
The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance. It is useful when a single shared resource is required across the entire application.
2. Factory Method Pattern
The Factory Method pattern defines an interface for creating objects, but allows subclasses to decide which class to instantiate. This pattern promotes loose coupling by delegating the responsibility of object creation to subclasses.
3. Abstract Factory Pattern
The Abstract Factory pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes. This pattern is useful when you need to create a group of objects that work together or have some common characteristics.
4. Builder Pattern
The Builder pattern separates the construction of a complex object from its representation, allowing the same construction process to create different representations. This pattern is useful when you need to create objects with a large number of optional or required components.
5. Prototype Pattern
The Prototype pattern creates new objects by copying an existing object (the prototype). This pattern is useful when object creation is expensive, and you want to reuse an existing instance with minor changes rather than create a new one from scratch.
Structural Design Patterns
Structural design patterns are concerned with the composition of classes and objects. They help to define the structure and relationships between different components in a system. Some common structural design patterns include:
1. Adapter Pattern
The Adapter pattern allows classes with incompatible interfaces to work together by wrapping one class with a new interface that matches the other class’s interface. This pattern is useful when you need to integrate existing components with different interfaces.
2. Bridge Pattern
The Bridge pattern decouples an abstraction from its implementation, allowing them to vary independently. This pattern is useful when you want to separate the interface of a component from its concrete implementation, making it easier to change or extend either part without affecting the other.
3. Composite Pattern
The Composite pattern composes objects into tree structures to represent part-whole hierarchies. This pattern allows clients to treat individual objects and compositions of objects uniformly. This pattern is useful when you need to represent a hierarchy of objects with a common interface.
4. Decorator Pattern
The Decorator pattern attaches additional responsibilities to an object dynamically without affecting the behavior of other objects. This pattern is useful when you want to add or override the behavior of an object without modifying its structure or affecting other instances of the same class.
5. Facade Pattern
The Facade pattern provides a simplified interface to a complex subsystem. This pattern is useful when you want to hide the complexity of a system and provide a simpler, unified interface for clients to interact with
6. Flyweight Pattern
The Flyweight pattern minimizes memory usage by sharing as much data as possible with other similar objects. This pattern is useful when you have a large number of objects with mostly shared or repeatable data, and you want to reduce memory consumption.
7. Proxy Pattern
The Proxy pattern provides a surrogate or placeholder object for another object to control access to it. This pattern is useful when you want to add a level of indirection to an object, such as for remote access, lazy instantiation, or access control.
Behavioral Design Patterns
Behavioral design patterns are concerned with the communication and interaction between objects. They help to define how objects collaborate to achieve a common goal. Some common behavioral design patterns include:
1. Chain of Responsibility Pattern
The Chain of Responsibility pattern allows an object to pass a request along a chain of potential handlers until one of them handles the request. This pattern is useful when you have a set of objects that can handle a request, and you want to determine which object should handle it at runtime.
2. Command Pattern
The Command pattern encapsulates a request as an object, allowing you to parameterize clients with different requests, queue or log requests, and support undoable operations. This pattern is useful when you want to decouple the sender of a request from its receiver, and you need to keep track of the requests or enable undo/redo functionality.
3. Interpreter Pattern
The Interpreter pattern defines a representation for a language’s grammar and provides an interpreter to evaluate expressions in the language. This pattern is useful when you have a specific language or syntax that needs to be interpreted and executed by your application.
4. Iterator Pattern
The Iterator pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation. This pattern is useful when you need to traverse a collection of objects uniformly, regardless of their concrete implementation.
5. Mediator Pattern
The Mediator pattern defines an object that encapsulates how a set of objects interact. This pattern promotes loose coupling by keeping objects from referring to each other explicitly and allows their interaction to be changed independently. This pattern is useful when you have a group of objects that need to communicate with each other, and you want to centralize their interaction in a single place.
6. Memento Pattern
The Memento pattern captures and externalizes an object’s internal state without violating encapsulation, allowing the object to be restored to this state later. This pattern is useful when you need to provide a snapshot or undo/redo functionality for an object’s state.
7. Observer Pattern
The Observer pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. This pattern is useful when you need to keep multiple objects synchronized with a single source of truth.
8. State Pattern
The State pattern allows an object to alter its behavior when its internal state changes. This pattern is useful when an object’s behavior depends on its state, and you want to encapsulate state-specific behavior within separate objects.
9. Strategy Pattern
The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. This pattern is useful when you have multiple ways to accomplish a task, and you want to select the appropriate algorithm at runtime based on specific conditions or inputs.
10. Template Method Pattern
The Template Method pattern defines the skeleton of an algorithm in an operation, deferring some steps to subclasses. This pattern allows subclasses to redefine certain steps of an algorithm without changing the algorithm’s structure. This pattern is useful when you have a common algorithm with some steps that need to be customized or overridden by subclasses.
11. Visitor Pattern
The Visitor pattern represents an operation to be performed on the elements of an object structure. This pattern allows you to define a new operation without changing the classes of the elements on which it operates. This pattern is useful when you need to perform various operations on a set of objects with different interfaces, and you want to separate the operation logic from the object structure.
How are the Design Patterns categorized?
Since there are many design patterns to be aware of, it’s essential to arrange those to refer and find easily. Design patterns are classified according to two criteria. One is the purpose of the pattern and the other is the scope of the pattern. Purpose highlights what a pattern does while scope specifies whether the pattern applies primarily to classes or to objects. Let’s view the standard pattern classification.
List of Properties of a Good Design Pattern
A good design pattern should possess several properties to be considered effective and beneficial for software development. Here is a list of properties that characterize a good design pattern:
- Solves a recurring problem: A good design pattern addresses a recurring problem or challenge that developers encounter in software design. It provides a generalized solution that can be adapted and applied in various situations.
- Reusable: A good design pattern is reusable and can be applied to multiple projects and scenarios. It should offer a flexible solution that can be tailored to fit different requirements and constraints.
- Understandable and easy to implement: A good design pattern should be easy to understand, with a clear explanation of its purpose, structure, and implementation. It should provide a step-by-step guide to help developers apply the pattern correctly and effectively.
- Scalable: A good design pattern should be scalable and able to accommodate the growth and expansion of a software system. It should support the addition of new features and components without requiring significant changes to the existing design.
- Maintainable: A good design pattern promotes maintainability by making it easier for developers to modify and update the software system. It should encourage modularity, separation of concerns, and loose coupling to simplify the process of making changes to the codebase.
- Consistent: A good design pattern should be consistent in its naming conventions, structure, and implementation. This consistency makes it easier for developers to recognize and understand the pattern when they encounter it in different projects or contexts.
- Well-documented: A good design pattern should be well-documented, with clear descriptions of its purpose, structure, implementation, and any variations or related patterns. This documentation helps developers understand the pattern’s benefits and limitations and how to apply it effectively.
- Encourages best practices: A good design pattern should encourage best practices in software design, such as separation of concerns, modularity, and code reusability. By promoting these principles, the pattern helps developers create more efficient, reliable, and maintainable software systems.
- Improves code readability: A good design pattern should improve the readability of the code by providing a clear structure and organizing related components logically. This makes it easier for developers to understand the codebase and reduces the potential for errors or misunderstandings.
- Adaptable: A good design pattern should be adaptable to different programming languages, frameworks, and platforms. This allows developers to apply the pattern across various technologies and environments, increasing its usefulness and versatility.
Design patterns provide valuable guidance for solving recurring problems in software design, but they are not a one-size-fits-all solution. There are certain things that design patterns don’t do or address, such as:
- Design patterns don’t solve all problems: While design patterns address common challenges in software design, they are not meant to solve every problem developers might face. There will be unique or specific problems that require tailor-made solutions rather than applying a general design pattern.
- Design patterns don’t replace creativity: Design patterns should not be seen as a replacement for creativity or innovative thinking. They serve as a tool to help developers solve common problems more efficiently, but they should not hinder the exploration of new ideas or techniques.
- Design patterns don’t guarantee an optimal solution: Implementing a design pattern does not guarantee that the solution will be the most efficient or best-fit for a particular problem. Depending on the specific requirements and constraints, there may be other solutions that perform better or are more appropriate.
- Design patterns don’t eliminate the need for planning: Design patterns provide guidance on structuring software, but they don’t replace the need for careful planning and analysis. Developers still need to thoroughly understand the problem they are trying to solve and choose the appropriate design pattern accordingly.
- Design patterns don’t dictate implementation: Design patterns offer a general structure or approach to solving a problem, but they do not dictate the exact implementation details. Developers need to adapt the pattern to fit the specific requirements and constraints of their project.
- Design patterns don’t address non-functional requirements: Design patterns mainly focus on the structural and behavioral aspects of software design. They don’t directly address non-functional requirements, such as performance, security, or usability, which are also crucial for the success of a software system.
- Design patterns don’t apply to every situation: Not every situation requires the use of a design pattern. Sometimes, simpler solutions may be more appropriate, or a design pattern may not be applicable due to specific constraints or requirements. Developers should carefully evaluate the problem at hand before deciding to apply a design pattern.
Design patterns are essential tools for software developers, but it’s crucial to consider some special notes and caveats when using them:
- Understand the problem before applying a pattern: Before selecting and implementing a design pattern, ensure you have a thorough understanding of the problem you’re trying to solve. Blindly applying a pattern without understanding the underlying issue can lead to unnecessary complexity or an inefficient solution.
- Choose the right pattern: There are numerous design patterns available, each addressing specific problems and scenarios. It’s essential to choose the most appropriate pattern that aligns with your project’s requirements and constraints.
- Avoid overuse of patterns: While design patterns can be helpful, it’s crucial not to overuse them. Excessive use of design patterns can lead to overly complex and hard-to-maintain code. Use design patterns judiciously, and only when they genuinely contribute to solving the problem at hand.
- Combine patterns when necessary: Sometimes, a single design pattern might not be sufficient to address a particular problem. In such cases, you can combine multiple design patterns to create a more comprehensive solution. This requires a deep understanding of the patterns involved and how they can be integrated effectively.
- Adapt patterns to your specific needs: Design patterns are meant to be flexible and adaptable. While they provide a general structure, you should modify them to suit your specific requirements and constraints. This may involve extending, refining, or even combining patterns to achieve the desired result.
- Patterns evolve over time: Design patterns are not set in stone. They evolve as developers gain more experience and insight into solving problems in software design. Be open to learning about new patterns or updates to existing ones, and stay informed about best practices in the field.
- Patterns are not language-specific: While design patterns may be described or implemented using specific programming languages, the concepts behind them are generally applicable across different languages and platforms. Understanding the underlying principles will allow you to implement the pattern in your language of choice.
- Consider performance implications: Implementing a design pattern may have performance implications for your application. Be sure to evaluate the impact of using a particular pattern on performance and consider alternative approaches if the pattern introduces significant overhead or reduces efficiency.
- Document your patterns: When using design patterns, it’s essential to document their usage and purpose within your codebase. This helps other developers understand the rationale behind your design choices and makes it easier for them to work with and maintain the code.
- Keep learning: Design patterns are a vast and ever-evolving field. Continuously expand your knowledge by reading books, articles, and participating in discussions related to design patterns. This will help you stay updated on the latest trends and best practices, making you a more effective software developer.
Design Patterns are still adding to the software field, and there are many more popular patterns in the community. This article illustrates the basic set of patterns introduced by Gang of Four in Design Patterns: Elements of Reusable Object-Oriented Software book. Learning design patterns is essential to stay unbeaten in within the experts. So, start learning from today if you are not still on the move.
4 thoughts on “Introduction to Design Patterns”
Be careful while using a design pattern. You should weigh the pros and cons of each pattern before you decide to use one. It may not make sense to use some patterns in smaller projects where the cons will outweighs the pros for a design pattern. You may end up with uncessay code like factories while you are only creating one object. So, evaluate your design patterns before using them.
You are right. Choosing a design pattern should be done carefully. Pros and cons need to be looked at to see if a pattern fits a problem. People should also be carful about the anti patterns
Which pattern can be used to replace a switch case statement.
Very well written article. Thanks