Lab 03: Bouncing Disks


  1. Accountability Group Assignments
    • arrange to meet this week
  2. Quiz 02 is actually happening this week
    • on objects and memory
  3. Rest of week:
    • finishing objects and memory
    • starting object inheritance

Lab 03: Bouncing Disks

Two new features:

  1. Object instances represented in graphical form
    • BouncingDisk
  2. Animation
    • draw/update loop

Quick Demo

Bouncing Disk

A BouncingDisk stores

  • position
  • velocity
  • radius
  • color

Primary instance methods

  • draw itself on a Graphics object
  • update its new state

Animation in Theory

  • Sequence of frames displayed in rapid succession
    • 24 fps $\implies \sim 42$ ms per frame for movies
    • $\sim 60$ fps $\implies \sim 17$ ms per frame modern broadcast
  • Each frame differs incrementally from previous
  • Gives illusion of motion

Animation in Code

Draw/update loop:

            world.update(1.0 / (double) FPS);
            catch(InterruptedException e){
		System.err.println("Thread interrupted.");

Animating Motion

A moving object:

  • position
  • velocity (speed + direction)
  • units: pixels / second
  • how to update for next frame?

How to Represent Bouncing?

Your Task

  1. Complete Pair class
    • reprsents vector $(x, y)$-coordinates
    • no explicit instructions
    • error messages tell you what is missing
    • remark: multiple constructors possible!
  2. Extensions
    • disks accelerate due to gravity?
    • disks change color over time?
    • disks interact with each other?

Assignment Demo

Download the Code