More Inheritance EEE321'10

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More Inheritance EEE321.10
Royal Military College of Canada Electrical and
Computer Engineering

• Maj JW Paul
• Jeff.Paul_at_rmc.ca
• 1-613-541-6000 x6656

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A true Geek2 test
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VI

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Review

• Name the two broad categories of polymorphism
• ad-hoc
• universal
• What are their key differences?
• Name the sub-categories
• ad-hoc
• overloading coercion
• universal
• sub-type inclusion parametric
• Give examples

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Todays Class

• Some modelling

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UML Relations Symbols
Dependencies
uses
Generalizations
kind of
bi-directional structural relation
Associations
Aggregation
part of relationships
Composition
see Booch p 73
ATM example
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Inheritance Tips

• Look for similarities
• Look for existing classes
• Follow the sentence rule
• A subclass IS A superclass
• A subclass IS A KIND OF superclass
• A subclass IS LIKE A superclass
• Avoid implementation inheritance
• Inherit everything

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Aggregation Tips

• Apply the sentence rule
• the part is PART OF the whole
• the whole HAS A part
• It should be part of the real world
• You should be interested in the part
• Show multiplicity and roles
• Aggregation is inherited

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Navigation

• Determines awareness of the relation

Not to be confused with the name and direction of
the relation
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Example
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Association Relationships

• Associations usually represent objects of one
  class making use of objects of another class

What cardinality should we add?
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Multiplicity (cardinality)
1 only one 1.. one or more 0..1 zero or
one 0.. zero or more (also )
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Aggregation vs Association

• It is not always obvious when to use association
  and when to use aggregation
• There are differing views in the OO world
• Aggregation often starts out as association, but
  as the semantics of the problem are refined an
  association can become aggregation
• More important at the implementation perspective

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When to use Aggregation

• The lifetime of the part is bound within the
  lifetime of the aggregate - there is a create
  delete dependency of the part on the whole.
• There is an obvious whole-part physical or
  logical assembly
• Some properties of the composite propagate to the
  parts, such as its location
• Operations applied to the composite propagate to
  the parts, such as destruction, movement,
  recording, etc.

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Aggregation Examples
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Composition

• A kind of aggregation
• Stronger relationship than plain aggregation
• The part object may belong to only one whole
• The parts live and die with the whole
• In implementation the component is structurally
  part of (a field of) the whole

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Composition
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Inheritance vs Composition
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Associations in Java

• What will they look like?

Components Aggregation Association
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Review
What are the core concepts of OO? decomposition ab
straction encapsulation hierarchy
From http//bdn.borland.com/article/0,1410,31863,
00.htmlclassdiagrams
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Review

• What are the fundamental relationships?
• Dependencies
• Generalizations
• Associations (aggregation composition)
• What are their key differences?