Design Patterns Tutorials

Introduction The Flyweight Pattern is a structural design pattern that minimizes memory usage by sharing as much data as possible between similar objects. Imagine a text editor rendering a document with thousands of characters. Each character needs a font, size, and color — but most characters…

Introduction The Composite Pattern is a structural design pattern that lets you compose objects into tree structures and then work with those structures as if they were individual objects. Think of a file system — a directory can contain files and other directories. Whether you ask for the size of…

Introduction The Iterator Pattern provides a way to access elements of a collection sequentially without exposing its underlying representation. Whether the data lives in an array, a linked list, a tree, or a paginated API, the iterator gives clients a uniform interface to traverse it: hasNext()…

Introduction The State Pattern allows an object to alter its behavior when its internal state changes, making it appear as though the object has changed its class. Instead of scattering state-dependent logic across methods with conditionals, you encapsulate each state into its own class, and the…

Introduction The Template Method Pattern defines the skeleton of an algorithm in a base class, letting subclasses override specific steps without changing the algorithm’s overall structure. The base class controls the workflow — the “what” and “when” — while subclasses provide the “how” for…

Introduction The Observer Pattern establishes a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. Think of it as a subscription model — interested parties register to receive updates, and the publisher broadcasts…

Introduction The Strategy Pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable at runtime. Instead of hardcoding behavior into a single class with conditionals, you extract each algorithm into its own class and let the client choose which one to use. This is…

Introduction The Decorator Pattern is a structural design pattern that lets you attach new behaviors to objects by wrapping them in special objects that contain the added behavior. Think of it like adding toppings to a coffee — you start with a base espresso, then wrap it with milk, then wrap that…

Introduction The Proxy Pattern is a structural design pattern that provides a substitute or placeholder for another object to control access to it. Just like a security guard controls access to a building — they do not change what is inside, but they decide who gets in and can log every entry — a…

Introduction The Adapter Pattern is a structural design pattern that allows objects with incompatible interfaces to work together. Think of it like a power adapter you use when traveling abroad — your laptop plug does not change, the foreign outlet does not change, but the adapter bridges the gap…

Introduction The Abstract Factory pattern provides an interface for creating families of related objects without specifying their concrete classes. While the Factory Method creates one product, the Abstract Factory creates an entire suite of products that are designed to work together. This is the…

Introduction The Prototype pattern creates new objects by cloning an existing instance rather than building one from scratch. When object creation is expensive — involving database queries, file I/O, or complex initialization — copying a pre-configured prototype is significantly faster. This…

Introduction The Facade Pattern is a structural design pattern that provides a simplified, unified interface to a complex subsystem. Think of ordering food at a restaurant — you simply tell the waiter what you want. Behind the scenes, the kitchen, inventory, and billing systems coordinate to…

Introduction The Factory Method pattern defines an interface for creating objects but lets subclasses decide which class to instantiate. Instead of calling a constructor directly, client code delegates creation to a factory method, which returns an object that conforms to a common interface. This…

Introduction The Builder pattern separates the construction of a complex object from its representation, allowing the same construction process to create different representations. It shines when an object requires many configuration options, optional parameters, or a specific construction sequence…

Introduction The Singleton pattern ensures a class has only one instance and provides a global point of access to it. It is one of the most widely used — and misused — design patterns in software engineering. When applied correctly, it solves real problems around shared resource management, such as…