OOPSLA 04 Educators Symposium

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OOPSLA 04 Educators Symposium

• Nifty Assignment The Shape Calculator

Eric Cheng, Dung Zung Nguyen, Mathias Ricken,
Stephen Wong
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Niftiness

• Swing GUI application with the MVC pattern.
• Closures via anonymous inner class
• Callback architecture
• Extensibility and security via factories
• Dynamic nature of OO programs
• Abstraction!

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What is a shape?
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What is a shape?

• Knows how to compute its area
• Knows how to present itself visually

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How do we make a shape?

• Constructor for a rectangle
• public Rect(double width, double height)
• Constructor for a circle
• public Circle(double radius)

How to call a constructor if its parameters are
unknown?
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Factory design pattern

• Factories know how.
• Can specify a clear definition of a factory we
  know how to make factories.

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Behavioral definitions

• IShapeFactory
• JPanel getPropertyPanel()
• IShape makeShape()
• IShape
• double getArea()
• void paint(Graphics g, int x, int y)

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Behavioral definitions

• Interfaces define behaviors.
• A factory is a factory if it satisfies the
  protocols a shape is a shape if it complies to
  our definition.
• No need to have explicit class definitions.
• Closures
• Can have not only area, but also colors!
• Dynamically load code at runtime

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Philosophical / Design Question

• Should the shape know about, or even have the
  factory?

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GUI builders for IDEs

• Rely on zero-ary public constructors for
  components.
• Breaks encapsulation.
• Violates definition of the component (is a shape
  a factory?)
• Can possibly break the system by creating an
  immature, but perfectly legal shape.

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Our goal

• The clear distinction and separation of
  responsibilities
• Each piece of component does what it is meant to
  do, and expose the appropriate amount of
  information

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Questions?