Design Patterns Explained

22 Part I An Introduction to Object-Oriented Software Development
Object-Oriented Programming in Action
New example Let’s re-examine the shapes example discussed at the beginning of
the chapter. How would I implement it in an object-oriented manner?
Remember that it has to do the following:
Using objects in the
Shape program
1. Locate the list of shapes in the database.
2. Open up the list of shapes.
3. Sort the list according to some rules.
4. Display the individual shapes on the monitor.
To solve this in an object-oriented manner, I need to define the
objects and the responsibilities they would have.
The objects I would need are:
Class Responsibilities (Methods)
ShapeDataBase getCollection—get a specified collection of
shapes
Shape (an
abstract class)
Square (derived
from Shape)
Circle (derived
from Shape)
display—defines interface for Shapes
getX—return X location of Shape (used for sorting)
getY—return Y location of Shape (used for sorting)
display—display a square (represented by this
object)
display—display a circle (represented by this
object)
Collection display—tell all contained shapes to display
sort—sort the collection of shapes
Display drawLine—draw a line on the screen
drawCircle—draw a circle on the screen