Object-Oriented Design & Design Patterns Roadmap

Learn object-oriented design from core modeling principles through SOLID, GRASP, GoF patterns, refactoring, and a practical design capstone.

published: reading time: 10 min read author: Geek Workbench
Quick Summary

Learn object-oriented design from core modeling principles through SOLID, GRASP, GoF patterns, refactoring, and a practical design capstone.

Object-Oriented Design & Design Patterns Roadmap

Object-oriented design is the work of assigning responsibilities to objects, defining the relationships between them, and keeping change from spreading through an application. Design patterns give names to recurring design choices, but they are most useful after you can recognize the problem and compare the cost of each solution.

This roadmap is for developers who can write small programs in an object-oriented language and want to design code that stays understandable as features grow. It starts with objects and relationships, moves through design principles and the Gang of Four pattern families, then applies the ideas to modeling, testing, and refactoring. At a part-time pace of five to seven hours a week, allow about ten to twelve weeks, including the capstone.

Before You Start

  • Be comfortable with one programming language, functions, collections, modules, and basic automated tests.
  • Know how to read a small class-based program. Prior UML experience is not required.
  • If classes and objects are new, first work through the Java Fundamentals Roadmap or the equivalent material for your language.

The Roadmap

1

📚 Object-Oriented Foundations

Encapsulation and Invariants
Inheritance and Subtyping
Polymorphism and Dynamic Dispatch
Composition, Delegation, and Object Collaboration
↓
2

🧠 Design Principles and Responsibility

SOLID Principles in Practice
GRASP: Assigning Object Responsibilities
Separation of Concerns, Cohesion, and Module Boundaries
Tell, Don't Ask and Law of Demeter
↓
3

🧩 Gang of Four Design Patterns

Creational Patterns: Control Object Creation
Structural Patterns: Compose Objects and Interfaces
Behavioral Patterns: Organize Collaboration
Choosing, Combining, and Removing Patterns
↓
4

🏗️ Modeling a Domain and Its Boundaries

Discovering Domain Concepts and Behaviors
Class Diagrams for Design Conversations
Value Objects, Entities, and Aggregates
Dependency Injection and Composition Roots
↓
5

🛠️ Applying and Evolving Object Designs

Testable Object Design and Collaborator Seams
Refactoring Toward Patterns Safely
Concurrency, Immutability, and Shared State
Design Review: Trade-Offs and Maintainability
↓
🎯

🎯 Capstone and Next Steps

Design a Small Order or Booking DomainModel the domain, assign responsibilities, implement a changing workflow, and explain which patterns you used or deliberately left out.
Java Fundamentals RoadmapReview classes, interfaces, generics, exceptions, and testing in Java.
Software Architecture Patterns RoadmapContinue from object boundaries to application and system architecture choices.

Timeline & Milestones

These estimates assume five to seven focused study hours a week. Spend extra time implementing each idea in your primary language; reading pattern descriptions alone is not enough to learn when they help.

📅

📅 Estimated Timeline

Weeks 1–2: Object-Oriented FoundationsRefactor a small example to protect invariants, clarify subtypes, and replace a rigid inheritance relationship with collaboration where it helps.
Weeks 3–4: Design Principles and ResponsibilityApply SOLID and GRASP heuristics to one feature; record which changes became easier and where extra indirection was not useful.
Weeks 5–6: Gang of Four PatternsImplement representative creational, structural, and behavioral patterns, then compare each with a simpler alternative.
Weeks 7–8: Domain Modeling and BoundariesModel a small business workflow, distinguish identity from value, and sketch only the class relationships that clarify the design.
Weeks 9–10: Applying and Evolving DesignsTest collaborators through stable seams, refactor in small steps, and reason about immutability and shared state.
Weeks 11–12: CapstoneBuild a small domain workflow, justify its responsibilities and patterns, and show how tests protect its important rules.
🎓

🎓 Capstone Track

Describe the DomainChoose an order, booking, or library workflow. Write its invariants, key use cases, and the changes the design should support.
Assign ResponsibilitiesSketch collaborators and their responsibilities. Identify one likely change point and compare a direct design with a pattern-based option.
Implement and ReviewDeliver one end-to-end behavior with tests, document trade-offs, and remove any abstraction that the evidence does not justify.

Milestone Markers

Milestone When What you can do
Foundation End of week 2 Explain object identity, encapsulation, subtyping, and collaboration in a small design.
Responsibility Design End of week 4 Assign behavior to objects and use SOLID or GRASP as focused review questions.
Pattern Fluency End of week 6 Recognize the GoF families and choose a pattern based on the problem forces and costs.
Domain Model Ready End of week 8 Represent a domain workflow with clear entities, values, and boundaries.
Capstone Complete End of week 12 Present tested code, a small design sketch, and a reasoned account of trade-offs.

Core Topics: When to Use / When Not to Use

Inheritance and Subtyping — When to Use vs When Not to Use
When to Use When NOT to Use
A subtype can honor the full contract of its parent wherever that parent is expected. A subclass needs to disable inherited behavior or violates assumptions callers rely on.
The hierarchy represents a stable, meaningful “is-a” relationship. The relationship exists only to reuse a few lines of implementation.
Shared behavior and variation are both clear and limited. Product combinations create many subclasses or changes ripple across the hierarchy.

Trade-off Summary: Inheritance offers direct substitutability and shared behavior, but it couples subclasses to the parent contract. Prefer composition when behavior varies independently or the relationship is only code reuse.

SOLID and GRASP — When to Use vs When Not to Use
When to Use When NOT to Use
A change repeatedly forces unrelated responsibilities to move together. Applying a principle creates interfaces and wrappers without a real change or test seam.
A class has unclear ownership or high-impact dependencies. A small, stable component is already easy to understand and modify.
Use the principles as questions during design and review. Treating every principle as a rule that must be maximized in every class.

Trade-off Summary: These principles help expose costly dependencies and misplaced responsibilities. They are heuristics; a design still needs to fit the scale, volatility, and team context of the problem.

Gang of Four Patterns — When to Use vs When Not to Use
When to Use When NOT to Use
The design has a recurring variation or collaboration problem the pattern directly addresses. A pattern is added because its name is familiar or expected in an interview answer.
The pattern makes an existing extension point or collaboration easier to explain. A conditional or direct call is clearer and the behavior is unlikely to vary.
The team can identify the added roles and test the resulting behavior. The pattern hides control flow or creates more indirection than the problem warrants.

Trade-off Summary: Patterns provide a shared vocabulary and tested design shapes, but every added role has a maintenance cost. Start from the forces and compare a simpler implementation before adopting one.

Entities, Value Objects, and Aggregates — When to Use vs When Not to Use
When to Use When NOT to Use
A domain concept has identity that persists across changes. Equality by identity adds no meaning to a simple immutable value.
A value is defined by its attributes and can be immutable. Modeling every data structure as a domain object adds ceremony without protecting a rule.
A consistency boundary needs to protect a group of related invariants. A proposed aggregate is so large that unrelated updates contend on one boundary.

Trade-off Summary: These distinctions help make identity, equality, and consistency explicit. Use only the modeling weight needed to keep the domain rules correct and comprehensible.

Dependency Injection — When to Use vs When Not to Use
When to Use When NOT to Use
A collaborator needs to vary across environments or tests. A dependency is stable, local, and obvious, and injection would obscure ownership.
Construction and runtime behavior benefit from being separated. A global container hides where objects come from or creates a service locator.
An application composition root can wire the graph explicitly. The object graph is small enough that direct construction remains simpler.

Trade-off Summary: Injection makes dependencies replaceable and visible at construction boundaries, while adding wiring and indirection. Keep composition explicit and avoid a container unless the graph justifies one.

Refactoring Toward Patterns — When to Use vs When Not to Use
When to Use When NOT to Use
Tests or another reliable check can preserve behavior during each small change. The desired abstraction is speculative and there is no current pressure to change the code.
A repeated change reveals a concrete variation point or misplaced responsibility. A large rewrite would combine behavior changes with structural changes.
Each step can leave the program in a working state. The team cannot validate important behavior or isolate regressions.

Trade-off Summary: Refactoring can make design intent clearer while preserving behavior, but it needs feedback and small steps. Add patterns in response to demonstrated forces rather than as a prediction exercise.

Resources

Category

roadmaps

Tags

#object-oriented-design #design-patterns #learning-path #study-guide

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