Objects

1
Objects

• Lecture OO04
• Representing Objects

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References

• Ambler, S., The Object Primer, Cambridge Univ.
  Press, 2001, Chapter 1 2, Sections 5.1 - 5.5

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Teaching Points

• Review of program memory organization
• Introduction to object constructors
• Investigation of object characteristics
• Singleton Pattern

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Review

• Vehicle example?
• Memory storage types

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Collaboration Diagrams (Objects)

• A type of Interaction Diagram
• Objects
• name
• type

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Object Characteristics

• State
• Behavior
• Identity

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State

• where in memory do objects go
• different constructor invocations
• destructor invocations

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Memory storage types

• Static Memory
• global variables
• static class members
• static function variables
• Automatic Memory (Stack)
• local variables
• function parameters
• Free Store (Heap)
• memory explicitly requested by programmer

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class ExampleClass int i //prim. type
variable stored with the //ExampleClass object
in heap AnotherClass handleName //handle
stored with ExampleClass object //note no
object exists AnotherClass yet static int
j //primitive type var. in static
memory //note one copy used for the whole
class static AnotherClass anotherName //handle
is stored in static mem //note no object
exists yet static anotherName new
AnotherClass() //new object is stored on the
heap //all instances use this single object
public ExampleClass handleName new
AnotherClass() //new object is stored on the
heap //each instance creates its own object
public someFunction() int i //prim.
type variable stored on the stack AnotherClass
someName new AnotherClass() //where??
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Behavior

• Objects accept messages
• Message can be function calls
• Modifier
• Selector
• Iterator
• Constructor
• Destructor

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Identity

• That property that distinguishes an object from
  all other objects
• mixing addressing w/ identity
• mixing data value with identity

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Discussion

• What about assignment?
• What about parameter passing?
• What about equivalence?
• What about garbage collection?

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Singleton Pattern

• Print Spooler
• Network Services object
• File System

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Teaching Points

• Review of program memory organization
• Introduction to object constructors
• Investigation of object characteristics
• Singleton Pattern