Software Design Patterns
The course teaches intermediate software design patterns, covering SOLID principles, creational, structural, behavioral, and architectural patterns, and shows how to select and apply them responsibly to improve code quality.
Who Should Take This
It is aimed at junior to mid‑level developers who have 1–3 years of experience with object‑oriented programming and are comfortable with classes, inheritance, and interfaces. These learners seek to deepen their ability to recognize appropriate patterns, evaluate trade‑offs, and avoid over‑engineering in real‑world projects.
What's Included in AccelaStudy® AI
Adaptive Knowledge Graph
Practice Questions
Lesson Modules
Console Simulator Labs
Exam Tips & Strategy
20 Activity Formats
Course Outline
67 learning goals
1
SOLID Principles
3 topics
Single Responsibility and Open-Closed
- Define the Single Responsibility Principle and identify violations in class designs where multiple unrelated behaviors are bundled into a single class.
- Apply the Single Responsibility Principle to decompose a monolithic class into cohesive, focused classes with clear ownership of a single concern.
- Describe the Open-Closed Principle and explain how designing classes to be open for extension but closed for modification reduces the risk of regression in existing code.
- Apply the Open-Closed Principle using inheritance, composition, or strategy injection to extend behavior without modifying existing classes.
Liskov Substitution and Interface Segregation
- Define the Liskov Substitution Principle and identify violations where subclass behavior contradicts the contract established by the base class.
- Analyze inheritance hierarchies for LSP violations including precondition strengthening, postcondition weakening, and invariant breaking and propose corrections.
- Describe the Interface Segregation Principle and explain how fat interfaces force implementing classes to depend on methods they do not use.
- Apply Interface Segregation by splitting a fat interface into focused role interfaces and demonstrate how clients benefit from depending only on the methods they need.
Dependency Inversion
- Define the Dependency Inversion Principle and explain the distinction between depending on abstractions versus concrete implementations.
- Apply Dependency Inversion using constructor injection, method injection, or interface-based abstractions to decouple high-level modules from low-level implementation details.
- Evaluate the trade-offs between tight coupling and abstraction overhead when applying Dependency Inversion and identify scenarios where direct dependencies are acceptable.
2
Creational Patterns
3 topics
Singleton and Factory Patterns
- Describe the Singleton pattern's intent, structure, and the problem it solves of ensuring a class has exactly one instance with a global access point.
- Analyze the drawbacks of the Singleton pattern including hidden dependencies, testability challenges, and thread safety issues and identify when alternative approaches are preferable.
- Describe the Factory Method pattern and explain how it delegates object creation to subclasses to decouple client code from concrete product classes.
- Apply the Factory Method pattern to replace conditional object creation logic with polymorphic factory classes that are open for extension.
Abstract Factory Pattern
- Describe the Abstract Factory pattern and explain how it creates families of related objects without specifying their concrete classes.
- Apply the Abstract Factory pattern to implement platform-independent UI component creation where each platform provides its own concrete factory.
- Analyze when to choose Abstract Factory over Factory Method based on whether the problem requires creating individual products versus families of related products.
Builder and Prototype Patterns
- Describe the Builder pattern and explain how it separates the construction of a complex object from its representation to allow the same construction process to create different representations.
- Apply the Builder pattern with a fluent interface to construct complex objects step by step, supporting optional parameters and validation at build time.
- Describe the Prototype pattern and explain how cloning existing objects avoids the cost of creating new instances from scratch when initialization is expensive.
- Apply the Prototype pattern using shallow and deep copy mechanisms and explain when each copy strategy is appropriate based on object composition.
3
Structural Patterns
3 topics
Adapter and Facade Patterns
- Describe the Adapter pattern (class adapter and object adapter variants) and explain how it enables incompatible interfaces to work together.
- Apply the Adapter pattern to integrate a third-party library with an incompatible interface into an existing codebase without modifying either side.
- Describe the Facade pattern and explain how it provides a simplified interface to a complex subsystem by hiding internal complexity behind a unified API.
- Apply the Facade pattern to wrap a multi-step workflow involving multiple subsystem classes into a single method call that orchestrates the interaction.
Decorator and Proxy Patterns
- Describe the Decorator pattern and explain how it attaches additional responsibilities to an object dynamically as an alternative to subclassing for extending functionality.
- Apply the Decorator pattern to compose behaviors by stacking multiple decorators around a core component, each adding a single concern (logging, caching, validation).
- Describe the Proxy pattern (virtual, protection, remote, caching variants) and explain how it controls access to another object by acting as a surrogate.
- Analyze the differences between Decorator, Proxy, and Adapter patterns and determine which is appropriate when the goal is extending behavior versus controlling access versus adapting interfaces.
Composite and Flyweight Patterns
- Describe the Composite pattern and explain how it composes objects into tree structures so that clients treat individual objects and compositions uniformly.
- Apply the Composite pattern to build a recursive tree structure (file system, UI component hierarchy, organizational chart) with consistent add, remove, and traverse operations.
- Describe the Flyweight pattern and explain how it uses shared intrinsic state to efficiently support large numbers of fine-grained objects.
- Analyze a scenario with thousands of similar objects to determine whether the Flyweight pattern provides meaningful memory savings given the ratio of intrinsic to extrinsic state.
4
Behavioral Patterns
4 topics
Observer and Mediator Patterns
- Describe the Observer pattern and explain how it defines a one-to-many dependency so that when one object changes state all its dependents are notified automatically.
- Apply the Observer pattern to implement an event notification system where publishers broadcast state changes to registered subscribers without tight coupling.
- Analyze the trade-offs between Observer and Mediator patterns for managing complex object interactions, considering coupling, reusability, and debugging complexity.
Strategy and State Patterns
- Describe the Strategy pattern and explain how it encapsulates interchangeable algorithms behind a common interface to allow runtime selection of behavior.
- Apply the Strategy pattern to replace conditional logic (switch/if-else chains) that selects among multiple algorithms with polymorphic strategy objects.
- Describe the State pattern and explain how it allows an object to alter its behavior when its internal state changes so that the object appears to change its class.
- Analyze the structural similarities and behavioral differences between Strategy and State patterns and determine which to use based on whether behavior selection is external or internal.
Command and Iterator Patterns
- Describe the Command pattern and explain how encapsulating requests as objects enables parameterization, queuing, logging, and undo/redo functionality.
- Apply the Command pattern to implement an undo/redo system by maintaining a history stack of executed command objects with inverse operations.
- Describe the Iterator pattern and explain how it provides a way to sequentially access elements of an aggregate without exposing its underlying representation.
- Apply the Iterator pattern to create custom traversal logic for complex data structures (trees, graphs, filtered collections) that decouples traversal from the structure itself.
Template Method and Chain of Responsibility
- Describe the Template Method pattern and explain how it defines the skeleton of an algorithm in a base class while letting subclasses override specific steps.
- Apply the Template Method pattern to implement a processing pipeline where the overall flow is fixed but individual processing steps vary by subclass.
- Describe the Chain of Responsibility pattern and explain how it passes a request along a chain of handlers until one handles it, decoupling sender from receiver.
- Analyze when to prefer Chain of Responsibility over conditional dispatching and evaluate how chain ordering and handler granularity affect maintainability.
5
Architectural Patterns
3 topics
MVC and MVVM Patterns
- Describe the Model-View-Controller pattern and explain the responsibilities of each component and how they interact through notifications and user input events.
- Apply the MVC pattern to separate data, presentation, and control logic in an application, ensuring the model has no knowledge of the view layer.
- Describe the Model-View-ViewModel pattern and explain how data binding between the View and ViewModel eliminates the need for the Controller role.
- Analyze the trade-offs between MVC, MVP, and MVVM for different application types (web, mobile, desktop) considering testability, complexity, and framework support.
Repository and Layered Architecture
- Describe the Repository pattern and explain how it mediates between the domain layer and data mapping using a collection-like interface for accessing domain objects.
- Apply the Repository pattern to abstract data access behind an interface that supports unit testing with in-memory implementations and swappable persistence layers.
- Describe layered architecture (presentation, business logic, data access, infrastructure) and explain how dependency rules govern the allowed direction of references between layers.
Event-Driven Architecture
- Describe event-driven architecture and explain how event producers, event channels, and event consumers interact to enable loose coupling between components.
- Apply event-driven patterns to decouple modules in a monolithic application using an in-process event bus with publish-subscribe semantics.
- Analyze the trade-offs of event-driven architecture including eventual consistency, debugging difficulty, event ordering challenges, and the benefits of temporal decoupling.
6
Anti-Patterns and Refactoring
3 topics
Code Smells and Anti-Pattern Recognition
- Identify common code smells (long method, large class, feature envy, data clumps, primitive obsession, divergent change, shotgun surgery) and describe the design problems each indicates.
- Describe the God Object, Spaghetti Code, Golden Hammer, and Lava Flow anti-patterns and explain the organizational and technical conditions that produce each.
- Analyze a codebase exhibiting multiple anti-patterns and prioritize which anti-patterns to address first based on their impact on maintainability and change frequency.
Refactoring Techniques
- Describe core refactoring techniques (Extract Method, Extract Class, Move Method, Replace Conditional with Polymorphism, Introduce Parameter Object) and their mechanical steps.
- Apply refactoring techniques to incrementally transform code toward a target design pattern without breaking existing functionality, using tests as a safety net.
- Evaluate when refactoring toward a design pattern is justified versus when the current design is sufficient, considering the YAGNI principle and change likelihood.
Over-Engineering and Pattern Misuse
- Identify signs of over-engineering including unnecessary abstractions, premature generalization, and pattern application without a clear problem to solve.
- Evaluate whether applying a design pattern to a given scenario adds genuine value or introduces accidental complexity, using criteria of current pain, change frequency, and team familiarity.
Hands-On Labs
15 labs
~385 min total
Console Simulator
Code Sandbox
Practice in a simulated cloud console or Python code sandbox — no account needed. Each lab runs entirely in your browser.
Scope
Included Topics
- SOLID principles: Single Responsibility, Open-Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion with practical examples in object-oriented languages.
- Creational design patterns from the Gang of Four catalog: Singleton, Factory Method, Abstract Factory, Builder, and Prototype, including their intent, structure, participants, and trade-offs.
- Structural design patterns: Adapter, Bridge, Composite, Decorator, Facade, Flyweight, and Proxy, including real-world analogies and when to apply each.
- Behavioral design patterns: Chain of Responsibility, Command, Iterator, Mediator, Memento, Observer, State, Strategy, Template Method, and Visitor, with emphasis on encapsulating behavior and reducing coupling.
- Architectural patterns at the application level: Model-View-Controller (MVC), Model-View-ViewModel (MVVM), Repository pattern, Event-Driven Architecture, and Layered Architecture.
- Anti-patterns and code smells: God Object, Spaghetti Code, Golden Hammer, Lava Flow, Premature Optimization, and systematic refactoring techniques to resolve them.
- Pattern relationships and composition: how patterns combine (e.g., Factory + Strategy, Observer + Mediator) and when to prefer one pattern over another for the same problem.
Not Covered
- Microservices patterns, service mesh patterns, and distributed systems patterns (Saga, Circuit Breaker, CQRS at the distributed level).
- Domain-Driven Design (DDD) tactical patterns including Aggregates, Value Objects, Domain Events, and Bounded Contexts.
- Framework-specific implementations (Spring dependency injection configuration, React component patterns, Angular module patterns).
- Concurrency patterns (Actor model, Producer-Consumer, Read-Write Lock) beyond brief mentions in behavioral pattern discussions.
- Functional programming patterns (Monads, Functors, Applicatives) that do not have direct OOP analogs.
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