CS226 -- Day 07 -- Spring 2013

JAVA REVIEW: Class Relationships

Composition & Aggregation: These are HAS-A relationships between
classes where one class contains members of another class.
Composition is for individual members (Person HAS-A String for name).
Aggregation is for collections of members (Deck HAS-A group of Cards).

Inheritance: A (derived, sub) class can be defined to EXTEND an
existing (base, super) class, inheriting all its data and methods.
This creates an IS-A relationship between classes where one subclass
is derived from a more general superclass.  For example: Sedan IS-A
Automobile, CheeseSteak IS-A Sandwich, Student IS-A Person.

Interface: This is a collection of method headers, no definitions,
possibly also some static data.  Interfaces may have many different
concrete implementations.  If a class IMPLEMENTS an interface it must 
contain a definition for every method in the interface.  An interface can
be used as a reference variable, but you can't create an actual object
of an interface type.  Instead the reference variable holds an object
from a class that IMPLEMENTS the interface.


Phase 1: Problem Definition

Suppose you want to create a program to keep a log of how you spend
your time - attending classes, doing homework, working, hobbies, etc.
It would provide ways to enter, edit and perhaps delete information,
as well as search for things like how much time you spent on a
particular course in a given week.

Phase 2: Design Solution

What classes would you create in designing an object oriented
solution?  Now think about similar programs that others may need:
keeping a work timesheet, various forms of exercise that comprise a
fitness plan, flight info for an airline, etc. Create a class system
that could solve all these related problems, not just the original
one.  Where would inheritance and interfaces come in handy?


Make a list of classes and interfaces, and the relationships between
them.  If you're familiar with UML diagrams, draw one to demonstrate
the elements of your design.

Comparable interface
Time interface extends Comparable
TimeMilitary implements Time: use 24 hour clock
TimeDate interface extends Time: date & time, compareTo, addHours,
addDays
Activity: name, start time, end time, getDuration
Event extend Activity: location
Database Interface: (work on collection of something), add, delete, find
Schedule Interface extends Database: (work on collection of Activities), can
add/delete/sort, getTotalTime(activity type)
ScheduleTable implements Schedule: HAS Activity

Flight extends Activity: fromAirport, toAirport
WorkTask extends Activity: client, billingRate
Exercise extends Activity: caloriesBurned

See activities.pdf for UML diagram of above classes & interfaces.


Now let's design some tests so that we will know if each interface is
properly implemented.  We have interface Time.java, implementation
TimeMil.java, and starter JUnit test file TimeTest.java.  See
junit.txt for an explanation of junit and how to run in a command-line
environment.  See on-line tutorials for how to use in Eclipse.