Inheritance-based Architecture

COMP 310 Java Resources Eclipse Resources

Fundamental Design Principle: The Separation of the Variant from the Invariant

What is an abstract ball?What is an abstract ball??
- The abstract ball, ABall
  - What methods are invariant?
    - An object is defined by its behaviors
  - What about fields? Does anyone on the outside care??
  - What is the process to update a ball?
    - What needs to be done?
    - Can the entire process be described in terms of concrete processes or not?
  - Bouncing off walls
    - The problem of discrete motion -- need to reset position back inside of animation canvas.
    - Calculating the reflected position (See homework instructions).
- Design patterns:
  - Singleton - in the supplied utility classes
  - Union - in the abstract-concrete ball heirarchy.
    - OpenStax/CNX module "Union Pattern: Inheritance and Polymorphism"
  - Observer-observable - in the dispatcher system
  - Template - in the ball updating method.
Concrete ABall implementations
- Union Design Pattern (see also: "Union Pattern: Inheritance and Polymorphism"))
- New ball instantiation issues
  - dynamic class loading
  - What needs to be specified?
- OpenStax/CNX web page on inheritance-based Ballworld -- Note that the design is slightly different than is presented here!

Union Design Pattern Balls:

The Union Design Pattern separates the system into variant and invariant parts along the line between the subclasses (variant) and the superclass (invariant).

The abstract ABall represents all the invariant properties and behaviors of balls, that is, all that is common across ALL balls.

The concrete subclasses, StraightBall, CurveBall, GooglyBall, etc. ONLY contain that which makes them distinct from other balls, that is, only that which is variant.

System design with Model-View-Controller (MVC) with Observer-Observable Design Pattern System:

Does the system care what kind of balls are in it?

Note that the number of adapters and the methods in those adapters depends on how you personally model the system. Your design may be different that what is shown here!