Thinking in Responsibilities

Have you ever built a class that felt too big, too scattered, or hard to modify? It’s one of the most common frustrations in object-oriented design. What if the problem wasn’t your code— but how you were thinking about it?

This section shifts your focus from syntax to mindset. Responsibility-Driven Design (RDD) isn’t just a technique—it’s a way of seeing software as a system of cooperating objects, each with a clear role. Instead of asking “What does this class do?” you start asking, “What responsibilities should this object own?”

By the end of this section, you’ll see how CRC cards become your thinking partners—not just tools for sketching, but instruments for clarifying intent, spotting design flaws early, and building models that evolve gracefully.

What This Section Covers

Each chapter is built around real design challenges and practical techniques to help you think more clearly about object roles and interactions.

• Responsibility-Driven Design: A Mindset Shift – Discover how shifting from “what the class does” to “what it’s responsible for” leads to more maintainable and testable software. Learn the core ideas behind object responsibility modeling and how CRC cards support RDD principles.
• Avoiding Overloaded or Misplaced Responsibilities – Identify when a class takes on too much or mixes unrelated duties. Use practical heuristics to correct common CRC modeling mistakes and apply responsibility assignment techniques to keep your models focused.
• Balancing Collaboration and Cohesion – Understand how cohesion and coupling influence your model’s stability. Learn how to balance class collaboration without fragmenting logic, applying modular CRC design and CRC coupling best practices.
• From CRC Cards to Class Diagrams – See how the insights from your CRC sessions naturally translate into UML class diagrams. Master the class diagram transition process, turning spontaneous design into structured, formal documentation.

By the end, you should be able to:

• Apply responsibility-driven design to model object behavior with clarity and intent.
• Recognize and refactor classes with misplaced or overloaded responsibilities.
• Balance collaboration and cohesion using CRC design principles.
• Convert CRC sessions into structured UML class diagrams for documentation or handoff.
• Use object modeling patterns to guide consistent and modular design decisions.
• Reflect on design choices through the lens of responsibility allocation and long-term maintainability.

These aren’t just steps—they’re habits of a thoughtful designer. You don’t need a perfect first pass. You just need to start thinking in responsibilities.