Design Patterns Study Notes

Abstract Factory Pattern

Provides an interface for creating families of related objects without specifying their concrete classes.

Adapter Pattern

The Adapter pattern converts the interface of a class into another interface clients expect, letting incompatible interfaces work together without modifying ex…

Anti-Patterns to Avoid

A tour of the most common design anti-patterns — recurring bad solutions to recurring problems — and how to recognize and refactor them before they calcify.

Builder Pattern

Separates the construction of a complex object from its representation, building it step by step.

Chain of Responsibility Pattern

A behavioral pattern that passes a request along a chain of handlers until one of them handles it, decoupling senders from receivers.

Choosing the Right Pattern

A practical framework for diagnosing the actual problem in your code first, then matching it to the smallest design pattern that resolves it, and avoiding comm…

Command Pattern

The Command pattern turns a request into a standalone object with a uniform execute() method, decoupling the invoker from the receiver and enabling undo, queui…

Composite Pattern

The Composite pattern composes objects into tree structures to represent part-whole hierarchies, letting clients treat individual objects and compositions of o…

Decorator Pattern

The Decorator pattern attaches additional responsibilities to an object dynamically by wrapping it in one or more decorator objects that share its interface.

Design Patterns in Modern Frameworks

How classic GoF design patterns show up, sometimes disguised under different names, inside React, Spring, Angular, and other modern frameworks.

Design Patterns Interview Questions

A focused prep guide covering the design-pattern questions most frequently asked in technical interviews, with the reasoning interviewers are actually testing…

Design Patterns Quick Reference

A condensed, scan-friendly cheat sheet mapping each core Gang of Four pattern to its intent, the force that triggers it, and a one-line example.

Facade Pattern

The Facade pattern provides a single, simplified interface to a larger, more complex body of subsystem code, making it easier to use without hiding advanced ac…

Factory Method Pattern

Defines an interface for creating an object but lets subclasses decide which concrete class to instantiate.

Iterator Pattern

A behavioral pattern that provides a way to access elements of an aggregate object sequentially without exposing its underlying representation.

Mediator Pattern

A behavioral pattern that centralizes complex communications between related objects into a single mediator object, reducing direct coupling.

Memento Pattern

A behavioral pattern that captures and externalizes an object's internal state so it can be restored later, without violating encapsulation.

Observer Pattern

The Observer pattern lets a Subject notify a dynamic list of Observers automatically whenever its state changes, decoupling event producers from consumers.

Prototype Pattern

Creates new objects by cloning an existing, pre-configured instance instead of constructing from scratch.

Proxy Pattern

The Proxy pattern provides a surrogate or placeholder object that controls access to another object, adding a layer for lazy loading, access control, caching,…

Refactoring to Patterns

How to evolve messy, ad-hoc code toward well-known design patterns incrementally, using the smell-driven refactoring approach popularized by Joshua Kerievsky.

Singleton Pattern

Ensures a class has only one instance and provides a single global point of access to it.

SOLID Principles Recap

A refresher on the five SOLID object-oriented design principles and how they form the underlying rationale for many Gang of Four design patterns.

State Pattern

The State pattern lets an object change its behavior when its internal state changes by delegating to interchangeable State objects that manage their own trans…