September 11, 2023
Last updated: January 5, 2024
Table of Contents
Creational Design Patterns are a category of design patterns that focus on the process of object creation in software development. They provide solutions for creating objects in a flexible and efficient manner while abstracting the actual instantiation process.
The Singleton design pattern ensures that a class has only one instance throughout the program’s execution. It provides a global point of access to that instance, making it useful for managing shared resources or configurations.
Singleton design pattern is often implemented by creating a private constructor and a static method to retrieve the sole instance. It helps control access to a resource, reducing the overhead of creating multiple instances. However, care should be taken to manage thread safety when implementing Singleton in multithreaded environments.
The Factory design pattern defines an interface for creating objects but delegates the responsibility of instantiation to its subclasses. It promotes loose coupling between the creator and the objects it creates, allowing for flexibility in object creation.
This pattern is useful when you want to customize object creation for different scenarios. It is prevalent in frameworks and libraries where the specific type of object to be created depends on user requirements. Factory design pattern methods can be overloaded or specialized in subclasses to accommodate diverse object creation logic.
The Abstract Factory pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes. It emphasizes creating objects with consistent interfaces across multiple product families.
This pattern is suitable for building complex systems where different parts must work together harmoniously. It’s particularly useful in scenarios where you need to ensure the compatibility of objects created together. Implementing an abstract factory involves defining multiple factory methods, each responsible for creating a different category of related objects.
The builder design pattern separates the construction of a complex object from its representation. It allows for the step-by-step construction of an object, providing fine-grained control over the process.
Builder design patterns are beneficial when you have objects with numerous optional components or configurations. Builders are responsible for assembling the parts and producing the final object, making it easier to create varied object configurations. It enhances code readability and maintainability by making the construction process more explicit and understandable.
The prototype design pattern involves creating new objects by copying an existing object, known as the prototype. It’s useful when object creation is more efficient through cloning rather than creating from scratch.
Prototype design patterns can simplify the creation of complex objects by allowing you to copy an existing, preconfigured instance. It helps in scenarios where the number of distinct object types is small, but there are many other possible configurations. Utmost care should be taken to manage the cloning process properly, especially for deeply nested or mutable objects.
Structural Design Patterns are a category of design patterns in software engineering that deal with the composition of classes or objects to form larger structures, thereby enhancing the organization and flexibility of a system.
These patterns focus on how objects and classes can be combined to form larger, more complex structures while keeping the system maintainable and adaptable. Structural design patterns are particularly useful when you want to ensure that the system remains scalable and easy to modify as it evolves. Some common structural design patterns include:
For example, if you have a legacy class that uses a certain interface, but you want to use a new class with a different interface, you can create an adapter to make the new class work seamlessly with the old one.
The Decorator design pattern is used to add additional behaviors or responsibilities to objects dynamically without altering their original structure. It involves creating a set of decorator classes that are used to wrap concrete components. Decorator design pattern enhances the functionality of objects in a flexible and reusable way.
For instance, in a text editing application, you can add decorators like “bold,” “italic,” or “underline” to modify the appearance of text without modifying the text class itself.
The Facade design pattern provides a simplified interface to a complex system, making it easier to interact with. The Facade design pattern acts as a high-level entry point to a set of interfaces or subsystems, shielding clients from the complexities of the underlying components. This simplifies client code and improves system maintainability.
The Proxy design pattern is used to control access to an object. It acts as a placeholder for another object to control access to it. This can be useful for various purposes, such as implementing lazy loading (loading an object only when it’s actually needed), access control, logging, or monitoring.
For instance, in a virtual proxy, a heavy object like an image is only loaded when it’s requested by the user, saving resources and improving performance.
These design patterns provide solutions to common design challenges and promote code reusability, flexibility, and maintainability in software systems.
Behavioral Design Patterns are a category of design patterns in software engineering that deal with how objects and classes interact and communicate with one another. These patterns focus on defining the responsibilities and collaborations between objects, emphasizing the behavior of objects within a system.
They provide solutions for managing complex communication flows, making systems more flexible, efficient, and maintainable. Behavioral design patterns are particularly useful when you want to improve the interaction between objects without introducing tight coupling or code duplication. Some common behavioral design patterns include:
The Chain of Responsibility design pattern is a behavioral design pattern that allows a chain of objects to process a request. Each object in the chain has the ability to either handle the request or pass it along to the next object in the chain.
The Chain of Responsibility design pattern promotes loose coupling between sender and receiver by letting multiple objects have a chance to handle a request without explicitly knowing which one will process it. It’s often used to implement logging systems, event propagation, or input handling.
Example: Imagine an online purchase approval process with different levels of authorization (e.g., employee, manager, director). Each level of authority is represented by an object in the chain. When a purchase request is made, the chain of authority objects checks if the request can be approved at their level. If not, they pass the request to the next level until it’s either approved or denied.
The Iterator design pattern is a behavioral pattern that provides a way to access elements of a collection sequentially without exposing its underlying representation. It defines an interface for iterating over a collection and encapsulates the traversal logic. This pattern enhances the flexibility of accessing elements, as different iterators can be implemented for the same collection, and clients can iterate over the collection without needing to know its structure.
For example, consider a bookstore where you want to iterate through a collection of books. The Iterator pattern allows you to create an iterator that abstracts the process of traversing the book collection. This way, you can iterate over the books using a common interface without worrying about how the books are stored internally.
The Observer design pattern is a behavioral pattern that defines a one-to-many dependency between objects. When the state of one object (the subject) changes, all its dependents (observers) are notified and updated automatically. This pattern is widely used in scenarios where objects need to maintain consistency across their relationships, such as UI updates in response to data changes.
For example, the observer design pattern can be applied in a weather monitoring application. The weather station (subject) tracks temperature, humidity, and pressure. Various displays (observers), such as a current conditions display, a forecast display, and a statistics display, subscribe to changes in the weather station. When the weather data changes, all the displays are notified and update their information accordingly.
The Dynamic Prototype Pattern is a design pattern used in software engineering to create objects by copying an existing object, known as a prototype, rather than creating new instances from scratch. This pattern is a variation of the Prototype Pattern, but it allows for more flexibility and dynamism in the creation of objects.