CRC Cards

1
CRC Cards

• Class-Responsibility-Collaborators
• Intended to keep design short and dynamic
• Helps keep code in reasonable places

2
CRC Cards

• One card per class
• Put a card onto the table for each object
  instance. This is the card for the external actor
  who triggers the use case.

3
CRC Cards

• Put a second card on the table. This is the card
  to whom the first card will send its initial
  message.
• Add cards for each new class you discover you
  need

4
Card Layout

• Each class should have only a handful of
  responsibilities (3-4)
• Each class should have only a handful of
  collaborators (3-4)

5

• The user enters a new command at the prompt in
  the interactions window. Once the user hits
  Enter, the command is executed, the result is
  displayed, and the cursor is moved down to a new
  prompt.
• Previous commands can be recalled to the
  current prompt using the up and down arrows,
  allowing the user to scroll through a history of
  commands.

6
Stories and CRC Cards

• Start with one story and walk through it,
  building the cards you need to complete it
• Then walk through other stories and see how well
  your cards hold up
• Add more cards as necessary

7
Additional Points

• Throw away cards if they become obsolete
• Each person can take charge of a card (or set of
  cards) and say when the card is useful during the
  story walkthrough