D.1.8

Construct related objects for a given problem.

Teaching Note:

In examinations problems will require the students to construct definitions for no more than three objects (JSR: I would say "classes", not "objects") and to explain their relationships to each other and to any additional classes defined by the examiners.

LINK Connecting computational thinking and program design.

AIM 4 Applying thinking and algorithmic skills to resolve problems.

Sample Question:

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JSR Notes:

"Construct related objects for a given problem"

This is where you will be given a certain problem/context, and you will decide how best to use abstraction to deconstruct the problem into sub-problmes, i.e. classes, and determine various useful relationships between those classes. There are lots of examples of this process here in Option D, and there will be lots more as we move foward. For example, see the "Bus" example of the sample Paper 2 exam, and any other Paper 2 past papers.

And already, with what we have done, you can take a look back at the example on D.1.4 which has four classes defined. And D.1.6 notes also has a couple of examples of objects/classes which have been chosen to address a certain larger problem.

Construction Steps

So on a test/exam, based on a certain new situation you will be asked to come up with:
- the decomposition of the problem, i.e. division of the overall problem into classes,
- that class structure's verticle heirarchy, if there are inheritance (i.e. "is-a") relationships,
- and any other connections between the classes, including "has a" and "uses" relationships.

Examples

Example Problem: Management of a bank's ATM application (keeping it to three classes only)

Client class: Requests both input and output from the ATM Machine
Machine class: Manages money by handling both input and output from user. So the Machine class uses objects of the Client class
Account class: Provides security by verifying users as they try to access the machine. The Client objects will "have" one or more Account objects.

Example Problem: Management of a Soccer Team (being more realistic with more than three classes)

TeamMember class: Class for all members of the organization, from backroom staff to players
NonPlayingStaff class: A sub-class of TeamMember, has CoachingStaff and Management below it on the heirarchy. So "is-a" TeamMember.
CoachingStaff class: A sub-class of NonPlayingStaff. So "is-a" NonPlayingStaff.
Management class: Also a sub-class of NonPlayingStaff. So "is-a" NonPlayingStaff.
Player class: A sub-class of TeamMember. So "is-a" TeamMember.
Goalie class: A sub-class of Player class. So "is-a" Player.
Stats class: "Uses" Player objects, and Goalie objects.
Lineup class: "Has-an" array of Players and Goalies

Example Problem: Keeping track of High School student attendance

Example Problem: Managing grades of students at a school

Or any other complex entity which could be defined by objects that make it up.

* In fact, do note that limiting the system to 3 classes makes the exercise trickier than it otherwise would be...