Gang of Four (GoF)

In 1994, as programming languages were evolving and gaining traction, four authors released a groundbreaking book titled Design Patterns — Elements of Reusable Object-Oriented Software. This influential work, authored by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, is often referred to as the Gang of Four (GoF). The book quickly became a bestseller and significantly impacted those interested in object-oriented programming.

Although it was initially framed in the context of C++, its relevance spans across all object-oriented languages, and it continues to be a top seller on platforms like Amazon.

Gang of Four Design Patterns

The authors introduced approximately 23 design patterns categorized into three main types: Creational, Structural, and Behavioral patterns.

• Creational Patterns: These patterns provide methods for creating objects, abstracting the instantiation process from the client. This allows for greater flexibility when determining which objects to create for specific scenarios. Examples include Singleton, Factory, and Builder.
• Structural Patterns: These patterns focus on the composition of classes and objects. They leverage inheritance to compose interfaces and establish methods for combining objects to enhance functionality. Examples include Adapter, Composite, and Decorator.
• Behavioral Patterns: These patterns deal with algorithms and the delegation of responsibilities among objects. They define not only the interactions between objects or classes but also the communication patterns among them. Examples include Interpreter, Observer, and State.

In this article, we will explore several key design patterns that I believe are essential for every developer in the software industry.

Note: The code examples in this article utilize Java, not Python.

Singleton Pattern

The Singleton pattern falls under the Creational category, where a single class is tasked with creating a singular instance of an object. This design ensures that only one object is instantiated, providing a method to access this instance directly, eliminating the need for additional instantiation. To enforce this, the class constructor is designated as private, restricting access to its members only. Common use cases for the Singleton pattern include cache management, database connections, and logging services.

Note: This illustration of the Singleton Pattern is not exhaustive. Various methods can breach the Singleton pattern, but there are strategies to safeguard against these violations. Here's a reference for creating an ideal Singleton class.

Factory Method Pattern

The Factory Method pattern is one of the most prevalent design patterns, serving as an effective way to create objects. As a Creational design pattern, it allows object creation without revealing the underlying logic to the client, utilizing a common interface through a factory method.

In this pattern, an interface or abstract class defines a method for object creation, delegating this task to one or more concrete subclasses during runtime. The subclasses implement the factory method to specify which class's objects to instantiate.

Decorator Pattern

The Decorator pattern enhances the functionality of specific objects dynamically at runtime without altering the behavior of other objects in the same class. This structural design pattern is particularly useful when additional functionalities need to be added to an object or its state modified during execution.

It follows a "pay-as-you-go" model; for instance, when ordering a pizza, you select the base like Margherita or Farmhouse, and then add toppings such as Fresh Tomatoes or Cheese Burst.

Adapter Pattern

The Adapter pattern facilitates cooperation between two incompatible classes by enveloping one with an interface compatible with the other. This structural design pattern, also referred to as a Wrapper, enables the conversion of a class's interface into another that a client prefers, typically involving a single class tasked with bridging the functionalities of incompatible interfaces.

State Pattern

The State design pattern enables an object to alter its behavior in response to changes in its internal state without modifying its class. Essentially, the object's behavior is contingent upon its state, allowing it to adapt when that state changes. This pattern belongs to the Behavioral category.

Design patterns are invaluable when applied in appropriate contexts, significantly enhancing the efficiency of software developers by leveraging tried-and-true solutions developed by experts over time, rather than relying on trial-and-error methods.

As with any programming concept, mastering these design patterns comes with practice through coding, which helps deepen your understanding of the underlying issues and the rationale for these solutions.

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