Class Design "Algorithm"

• Useful for tacking "designer's block"

Some Criteria for Evaluating Designs

• Coupling
  • The degree to which two classes (or methods) are "tied together." How likely is it that changing the internals of one will require modification of the other.
  • We aim for LOW coupling.
• Cohesion
  • The degree to which the components of a class "hang together".
  • Each class class should represent a single well-defined idea.
  • We aim for HIGH cohesion.

Mimp Design

Dotted arrows represent a dependency.

Diamond represents aggregation.

Possible Design Change 1

• Modify the Image class by removing getPixel/setPixel and replacing them with methods like:

  • getRed(int x, int y)
  • getGreen(int x, int y)
  • getBlue(int x, int y)
  • setPixelColor(int x, int y, int red, int green, int blue)
• (The Image class will still use Pixel objects internally)
• How would this impact coupling and cohesion? Is it a good idea?
  • Eliminates coupling between Pixel and ImageTransforms
  • Increases coupling between Image and Pixel
  • Maybe reduces the cohesion of Image
  • Good idea? Maybe. It's not crazy.

Possible Design Change 2

• Move image transform methods into Image class and make them non-static:
  • Image gray = colorImage.convertToGrayscale();
• How would this impact coupling and cohesion? Is it a good idea?
  • Reduces coupling (in a sense) by getting rid of one class altogether.
  • Negative impact on cohesion.
  • Probably not a good idea.

Possible Design Change 3

• Image Load/Save methods are only used by the GUI. Let's move them into MimpAPP.
• How would this impact coupling and cohesion? Is it a good idea?

Possible Design Change 4

• Image Load/Save methods are a static. Let's move them into ImageTransforms with the other static methods.
• How would this impact coupling and cohesion? Is it a good idea?