Object Oriented Design

CRC Cards

As you list responsibilities and collaborators, think about the member functions the collaborators might need to help with the task.
Example: To computer the total, the invoice needs to ask each item about its total price.
- Therefore the Item class is a collaborator.
- Does the Item class have a "get total price" member function? If not, add one to its card.
Many people find it helpful to group cards on a table so that the collaborators are close to each other, and to simulate tasks by moving tokens (such as a coin) from one card to the next to indicate which object is currently active.
Responsibilities that you list on the CRC card are on a high level, and may need two or more member functions for carrying out.
The CRC method is an informal process:
- Be creative and discover the classes and their responsibilities.
- Cross out, move, or split responsibilities.
- Rip cards up if they become too messy.