An Introduction to Java and Program Design - Java Programming: Comprehensive Concepts and Techniques - page 42

5 Understanding Event Diagrams

Refer to the event diagram in Figure 1-27 to answer the following questions:

Track sensor detects
approaching train

Approaching train
detected

Traffic signal
turns red

Time and date
register with
recorder

Sensor detects gates
begin to lower

Gates begin
to lower

Bell rings

Sensor detects
gates down

Gates complete
lowering

Train
proceeds

FIGURE 1-27

1. List each message and its corresponding operation.
2. Which of these operations triggers a subsequent message? List any such
operation and its subsequent message.
3. Which of these operations changes the value of an attribute of an object?
List the operation, the attribute, and the attribute's value before and after the
operation.

6 Creating a Generalization Hierarchy

Pick any class of objects that interests you (for example, books, clothes, musical
instruments, physical fitness equipment). Create a generalization hierarchy
showing at least four levels of subclasses and superclasses. For each subclass,
identify several attributes inherited from the superclass.

7 Creating Class Diagrams

Draw a class diagram for each object in Figure 1-27. Include at least two attri-
butes and one method in each diagram.

8 Creating an Event Diagram

Using Figure 1-27 as an example, draw an event diagram to raise the gates when
the track sensor has detected the train is clear of the intersection. The trigger is
the lack of weight on the tracks. The events that happen include the sensor
detecting that loss of weight and the gates rising. Possible operations include
traffic signal changing, time and date recording, and gate movement.