Sams Teach Yourself C++ in 21 Days

This simple interaction diagram shows the interaction among a number of design classes

over time. It suggests that the ATMclass delegates to the CheckingAccountclass all

responsibility for managing the balance, while the CheckingAccountcalls on the ATMto

manage display to the user.

Interaction diagrams comes in two flavors. The one in Figure 11.21 is called a sequence

diagram. Another view on the same information is provided by the collaboration dia-

gram. The sequence diagram emphasizes the sequence of events over time; the collabora-

tion diagram emphasizes the “timeless” interactions among the classes. You can generate

a collaboration diagram directly from a sequence diagram; tools such as Rational Rose

automate this task at the click of a button (see Figure 11.22).

364 Day 11

FIGURE11.22

Collaboration

diagram.

Customer

AT M

Checking

Account

1: Check Balances

2: Get Balance

3: Display Balance

6: Print

4 : Withdraw cash

5 : Dispense

Receipt

State Transition Diagrams

As you come to understand the interactions among the objects, you also have to under-

stand the various possible statesof each individual object. You can model the transitions

among the various states in a state diagram (or state transition diagram). Figure 11.23

shows the various states of the CustomerAccountclass as the customer logs in to the

system.

Every state diagram begins with a singlestartstate and ends with zero or more end

states. The individual states are named, and the transitions might be labeled. The guard

indicates a condition that must be satisfied for an object to move from one state to

another.