Objects and Object-Oriented Programming

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Objects and
Object-Oriented Programming

• CS 110 Honors
• Slides by Wanda Dann, Ithaca College

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Objects

• What is an object ?
• any thing that can be identified as unique from
  other things
• How is an object identified as unique?
• has a name
• has properties
• width, height, color, location, age, ss, id
• has a purpose
• associated actions it can perform
• tasks it can carry out

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Class

• Objects are categorized into classes
• Each object is
• an instance of the class.
• All objects in a class have similar properties
  and generally can perform the same tasks.

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Objects in a Virtual World

• In Alice, each 3-D model is an object
• has a unique name
• Bunny, Bunny1, Bunny2
• has color(s)
• Pink, White, Grey, Black, Blue, .
• has 3 dimensions
• height, width, depth

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Object Orientation

• Each object has 6 degrees of orientation
• front, back, left, right, up, down
• Orientation is relative to the object itself
• Bunny.move(left, 1, )
• is a move to the Bunny's left
• But, an object is aware of its orientation
  relative to other objects
• Bunny.pointAt(Helicopter)

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3-D Space

• An object is located in 3-D space

y
(0,0,0)
x
x is left - right y is up - down z is front -
back
z
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Repositioning

• Movement of an object changes its position in
  space.
• Some movements are translational
• Bunny.move(back, 0.5, )
• Other movements are rotational
• Bunny.turn(left, 0.5, )

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Motion Distance

• Translational Distance
• 1 unit is about 1 meter (relative to the Virtual
  World dimensions)
• Rotational Distance
• 1 unit is 1 rotation (360 degrees -- full turn)
• Can specify
• fractional parts of a unit
• 1/2
• 0.5
• multiple units
• 2

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Instructions

• An instruction such as
• Bunny.move(left, 1, )
• is a statement that asks an object to perform
  an action or carry out a task.
• Instructions must follow certain rules of syntax
  
• objectName.actionName(argumentList)
• Note
• Instructions may have 0, 1, 2, or more
  arguments
• Some arguments are optional, some are required

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Time

• Animation takes time -- even on fancy computers!
• By default, executing an instruction in Alice
  takes 1 unit of time (approx. 1 second)
• You can specify the amount of time
• Bunny.move(left, 1, duration 2)
• Note This instruction would slow down the move
  -- how could you speed it up?

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Object Parts

• Many objects are made up of parts (we say they
  are composites)
• A part of an object moves
• with the entire object, by default
• on its own, if given a specific instruction
• Bunny.head.leftear.turn(down, 1/8)
• Syntax
• objectName.partNameList.actionName(argumentList)

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Object-Oriented Programming

• An Alice program is
• a scene containing
• stationary objects -- like props on a stage
• active objects -- will move around the scene
• a list of instructions that ask the objects to
  perform tasks in the virtual world
• So, an Alice program is object-oriented.

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Reading and Lab

• See handouts.
• Note Lab exercises and projects require that
  you show me the code and execution of the
  programs created. I must "initial" your lab
  sheet for the exercises and projects or you will
  not get credit for them!