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Software Design Patterns Tutorial

Last Updated : 22 Apr, 2024
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Software design patterns are communicating objects and classes that are customized to solve a general design problem in a particular context. Software design patterns are general, reusable solutions to common problems that arise during the design and development of software. They represent best practices for solving certain types of problems and provide a way for developers to communicate about effective design solutions.


Types of Software Design Patterns

There are three types of Design Patterns:

  • Creational Design Pattern
  • Structural Design Pattern
  • Behavioral Design Pattern

Creational Design Patterns

Creational Design Pattern abstract the instantiation process. They help in making a system independent of how its objects are created, composed and represented.

Types of Creational Design Patterns:


1. Factory Method Design Pattern

The Factory Method pattern is used to create objects without specifying the exact class of object that will be created. This pattern is useful when you need to decouple the creation of an object from its implementation.

2. Abstract Factory Method Design Pattern

Abstract Factory pattern is almost similar to Factory Pattern and is considered as another layer of abstraction over factory pattern. Abstract Factory patterns work around a super-factory which creates other factories.

3. Singleton Method Design Pattern

The Singleton method or Singleton Design pattern is one of the simplest design patterns. It ensures a class only has one instance, and provides a global point of access to it.

4. Prototype Method Design Pattern

Prototype allows us to hide the complexity of making new instances from the client. The concept is to copy an existing object rather than creating a new instance from scratch, something that may include costly operations. The existing object acts as a prototype and contains the state of the object.

5. Builder Method Design Pattern

Builder pattern aims to “Separate the construction of a complex object from its representation so that the same construction process can create different representations.” It is used to construct a complex object step by step and the final step will return the object.

Structural Design Patterns

Structural Design Patterns are concerned with how classes and objects are composed to form larger structures. Structural class patterns use inheritance to compose interfaces or implementations.

Types of Structural Design Patterns:


1. Adapter Method Design Pattern

The adapter pattern convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn’t otherwise because of incompatible interfaces.

2. Bridge Method Design Pattern

The bridge pattern allows the Abstraction and the Implementation to be developed independently and the client code can access only the Abstraction part without being concerned about the Implementation part.

3. Composite Method Design Pattern

Composite pattern is a partitioning design pattern and describes a group of objects that is treated the same way as a single instance of the same type of object. The intent of a composite is to “compose” objects into tree structures to represent part-whole hierarchies.

4. Decorator Method Design Pattern

It allows us to dynamically add functionality and behavior to an object without affecting the behavior of other existing objects within the same class. We use inheritance to extend the behavior of the class. This takes place at compile-time, and all the instances of that class get the extended behavior.

5. Facade Method Design Pattern

Facade Method Design Pattern provides a unified interface to a set of interfaces in a subsystem. Facade defines a high-level interface that makes the subsystem easier to use.

6. Flyweight Method Design Pattern

This pattern provides ways to decrease object count thus improving application required objects structure. Flyweight pattern is used when we need to create a large number of similar objects.

7. Proxy Method Design Pattern

Proxy means ‘in place of’, representing’ or ‘in place of’ or ‘on behalf of’ are literal meanings of proxy and that directly explains Proxy Design Pattern. Proxies are also called surrogates, handles, and wrappers. They are closely related in structure, but not purpose, to Adapters and Decorators.

Behavioral Design Patterns

Behavioral Patterns are concerned with algorithms and the assignment of responsibilities between objects. Behavioral patterns describe not just patterns of objects or classes but also the patterns of communication between them. These patterns characterize complex control flow that’s difficult to follow at run-time.

Types of Behavioral Design Patterns:


1. Chain Of Responsibility Method Design Pattern

Chain of responsibility pattern is used to achieve loose coupling in software design where a request from the client is passed to a chain of objects to process them. Later, the object in the chain will decide themselves who will be processing the request and whether the request is required to be sent to the next object in the chain or not.

2. Command Method Design Pattern

The Command Pattern is a behavioral design pattern that turns a request into a stand-alone object, containing all the information about the request. This object can be passed around, stored, and executed at a later time

3. Interpreter Method Design Pattern

Interpreter pattern is used to defines a grammatical representation for a language and provides an interpreter to deal with this grammar.

4. Mediator Method Design Pattern

It enables decoupling of objects by introducing a layer in between so that the interaction between objects happen via the layer.

5. Memento Method Design Patterns

It is used to restore state of an object to a previous state. As your application is progressing, you may want to save checkpoints in your application and restore back to those checkpoints later. Intent of Memento Design pattern is without violating encapsulation, capture and externalize an object’s internal state so that the object can be restored to this state later.

6. Observer Method Design Pattern

It defines a one-to-many dependency between objects, so that when one object (the subject) changes its state, all its dependents (observers) are notified and updated automatically.

7. State Method Design Pattern

A state design pattern is used when an Object changes its behavior based on its internal state. If we have to change the behavior of an object based on its state, we can have a state variable in the Object and use the if-else condition block to perform different actions based on the state.

8. Strategy Method Design Pattern

The Strategy Design Pattern allows the behavior of an object to be selected at runtime. It is one of the Gang of Four (GoF) design patterns, which are widely used in object-oriented programming. The Strategy pattern is based on the idea of encapsulating a family of algorithms into separate classes that implement a common interface.

9. Template Method Design Pattern

Template method design pattern is to define an algorithm as a skeleton of operations and leave the details to be implemented by the child classes. The overall structure and sequence of the algorithm are preserved by the parent class.

10. Visitor Method Design Pattern

It is used when we have to perform an operation on a group of similar kind of Objects. With the help of visitor pattern, we can move the operational logic from the objects to another class.

Design Patterns in C++

Design patterns in C++ help developers create maintainable, flexible, and understandable code. They encapsulate the expertise and experience of seasoned software architects and developers, making it easier for newer programmers to follow established best practices.

Design Patterns in Java

Design patterns in Java help developers create more maintainable, flexible, and understandable code. They encapsulate the expertise and experience of seasoned software architects and developers, making it easier for newer programmers to follow established best practices.

Design Patterns in Javascript

JavaScript design patterns are the reusable solutions that are applied to commonly occurring issues/problems in writing JavaScript web applications. They actually help us to make our code more robust (strong). These patterns actually help to write organized, beautiful and well-structured codes.

Design Patterns in Python

Design Patterns in Python introduces a powerful and essential concept in software development – design patterns. These patterns offer time-tested solutions to recurring design problems, providing a structured and efficient approach to building robust, scalable, and maintainable software systems in Python.

Interview Questions on Software Design Patterns

Frequently Asked Questions About Software Design Patterns

1. What are software design patterns?

  • Software design patterns are reusable solutions to common problems that arise during software development. They are templates for solving recurring design issues and provide a way to create flexible, scalable, and maintainable software systems.

2. Why are design patterns important in software development?

  • Design patterns promote best practices, enhance code readability, and facilitate code reuse. They help in creating software that is modular, extensible, and easier to maintain, reducing development time and efforts.

3. How do design patterns differ from algorithms?

  • Design patterns focus on solving recurring design problems at the architectural or structural level, emphasizing the organization of code. Algorithms, on the other hand, are step-by-step procedures for solving specific problems at the computational level.

4. What are the common types of design patterns?

  • Design patterns are categorized into three main types: creational, structural, and behavioral. Creational patterns deal with object creation, structural patterns with object composition, and behavioral patterns with object collaboration and responsibility.

5. Can you provide examples of creational design patterns?

  • Examples include Singleton (ensuring a class has only one instance), Factory Method (creating objects without specifying the exact class), and Abstract Factory (providing an interface for creating families of related or dependent objects).

6. How do design patterns enhance code flexibility?

  • Design patterns promote loose coupling between components, making it easier to replace or extend parts of the system without affecting others. This flexibility is crucial for adapting to changing requirements.

7. When should I use design patterns?

  • Design patterns should be used when you encounter recurring problems in software design. They are particularly beneficial in complex systems where a systematic and proven approach to design is required.

8. Are design patterns language-specific?

  • No, design patterns are not tied to a specific programming language. They are conceptual solutions that can be implemented in various languages. However, the syntax and implementation details may vary.

9. How can I learn and master design patterns?

  • Start by understanding the basic principles of design patterns. Practice implementing them in your projects and study real-world examples. Books, online tutorials, and practical application in projects contribute to mastering design patterns.

10. Are design patterns applicable in all software projects?

  • While design patterns offer valuable solutions to common design problems, their applicability depends on the context and complexity of the project. In simpler projects, some patterns may be unnecessary, while in larger projects, they can be instrumental in maintaining a scalable and organized codebase.

11. What’s the difference between a design pattern and an anti-pattern?

  • Design patterns are proven solutions to common problems, promoting best practices. In contrast, anti-patterns are common pitfalls or bad practices that can lead to poor software design and should be avoided.

12. Can design patterns be overused?

  • Yes, overusing design patterns without considering the context and complexity of the project can lead to unnecessarily complex code. It’s important to apply design patterns judiciously, where they add value and improve code structure.

13. Can I create my own design patterns?

  • Yes, you can create custom design patterns based on your project’s specific needs. However, it’s crucial to ensure that the pattern addresses a recurring problem and follows the principles of good design.

14. How do design patterns relate to code smell?

  • Design patterns help eliminate code smells (indications of poor design) by providing proven solutions to common problems. Recognizing and addressing code smells is essential for creating maintainable and efficient software.

15. Are there design patterns for database design?

  • While traditional design patterns may not directly apply to database design, principles like normalization and denormalization can be considered as design patterns for creating efficient and scalable database structures.

16. Can design patterns be used in microservices architecture?

  • Yes, design patterns can be applied in microservices architecture to address common challenges such as service discovery, communication between services, and fault tolerance. Patterns like the Service Registry and Circuit Breaker are relevant.

17. How do design patterns impact system performance?

  • Properly applied design patterns can enhance system performance by promoting efficient code organization and reducing redundancy. However, poorly chosen or overused patterns may introduce unnecessary complexity, potentially impacting performance.

18. Do junior developers need to learn design patterns?

  • While not mandatory, learning design patterns can significantly benefit junior developers by providing them with proven solutions to common problems. It can expedite the learning process and contribute to writing more maintainable code.

19. How do design patterns contribute to code documentation?

  • Design patterns inherently document solutions to common design problems. When developers are familiar with design patterns, the code becomes self-documenting, making it easier for others to understand and contribute to the project.

20. Can design patterns be applied retroactively to existing codebases?

  • Yes, design patterns can be applied retroactively, but the process may involve refactoring existing code. It’s crucial to assess the impact of introducing a pattern and ensure that it aligns with the overall architecture.

21. Are there design patterns for web development?

  • Yes, many design patterns are applicable in web development. Patterns like MVC, Observer, and Singleton are commonly used to organize and structure code in both frontend and backend development.

22. How do design patterns differ from architectural patterns?

  • Design patterns address specific design issues at a lower level, focusing on object creation, composition, and interaction. Architectural patterns, on the other hand, deal with higher-level structures of an entire application or system.

23. Can design patterns be used in functional programming?

  • Yes, design patterns can be adapted for functional programming paradigms. Functional design patterns focus on composing functions to solve problems and promote immutability and statelessness.

24. What role do design patterns play in code maintainability during team collaboration?

  • Design patterns contribute to code maintainability by providing a common vocabulary and structure. When a team is familiar with design patterns, collaboration becomes more efficient, and team members can understand and reason about the codebase more easily.

25. Are there design patterns specifically for real-time systems?

  • Yes, real-time systems often utilize design patterns tailored to address their unique challenges. Patterns like the Observer pattern can be applied to handle real-time event notification and synchronization.

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