COMP 310 Spring 2017	Lec07: Designing a Ball

Ballworld Design

• 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.
      • Observer-observable - in the dispatcher system
      • Template - in the ball updating method.
  • Concrete ABall implementations
    
    • Union Design Pattern  (see also:: http://cnx.org/content/m11796/latest//))
    • New ball instantiation issues 
      • dynamic class loading
      • What needs to be specified?
• Animation technique
  • "Flipbook" animations -- create motion by diplaying different images at regular time intervals : 
    • Animation with still photos
    • Line drawing animation
  • javax.swing.Timer -- creates the "tick" that drives the animation process
  • Observer-observable -- Connects the timer tick to each ball via a "dispatching" process
    • The rest of the code does not care how the balls are notified, that is, the rest of the code is "decoupled" from the dispatching process.
    • ==> This means that the model code should delegate to something else to handle the dispatching process, i.e. delegate to a Dispatcher object to handle the updating of the balls.
    • Delegation results from the decoupling of the parts of a system.

Design patterns as expressions of CS principles:

To look for design patterns in the problem is to look for the underlying CS prinicples that are driving it.   The design patterns and the abstract notions that they represent comprise the "chunks" into which a problem is decomposed in order to understand it -- "Abstract decomposition"

HW02 homework instructions

© 2017 by Stephen Wong