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1.
CheckPoint: Interfaces and Communication
Messages
Understanding
object-oriented methodologies is often difficult. You already understand that
object-oriented analysis and design emulates the way human beings tend to think
and conceptualize problems in the everyday world. With a little practice,
object-oriented programming will become second nature to you.
As an example, consider
a typical house in which there are several bedrooms, a kitchen, and a laundry
room—each with a distinct function. You sleep in the bedroom, you wash clothes
in the laundry room, and you cook in the kitchen. Each room encapsulates all
the items needed to complete the necessary tasks.
You do not have an oven
in the laundry room or a washing machine in the kitchen. However, when you do
the laundry, you do not just add clothes to the washer and wait in the laundry
room; once the machine has started, you may go into the kitchen and start
cooking dinner. But how do you know when to go back to check the laundry? When
the washer buzzer sounds, a message is sent to alert you to go back into the
laundry room to put in a new load. While you are folding clothes in the laundry
room, the oven timer may ring to inform you that the meat loaf is done.
What you have is a set of well-defined
components: Each provides a single service to communicate with the other
components using simple messages when something needs to be done. If you
consider a kitchen, you see it is also composed of several, smaller components,
including the oven, refrigerator, and microwave. Top-level objectsare
composed of smaller components that do the actual work. This perspective is a
very natural way of looking at our world, and one with which we are all
familiar. We do the same thing in object-oriented programming:
o Identify
components that perform a distinct service
o Encapsulate
all the items in the component necessary to get the job done
o Identify
the messages that need to be provided to the other components
Although the details can be quite complex, these details are
the basic principles of object-oriented programming.
·
Consider the microwave oven in your kitchen, using the object-oriented
thinking described above.
·
Create a table with the following four column headings: Top-Level
Objects, Communicates With, Incoming Messages, and Outgoing Messages.
o Identity the top-level objects of
the microwave.
o Explain some of the graphical
user interfaces (GUIs) and communications messages that occur during the
operation of a microwave.
·
Describe some of the advantages of having a componentized system.
For example, what happens if the microwave breaks?
·
Post your completed CheckPoint as an attachment.
