Class Relationships

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Class Relationships

• Lecture Oo10
• Dependencies

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References

• Booch, et al, The Unified Modeling Language User
  Guide, Chapt 5 p.69, Chapt 9 130, Chapt 10 p.137.
• Gamma, Helm, Johnson, Vlissides, Design Patterns,
  AWL, 1995

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Teaching Points

• Dependency
• Parameterized Classes
• Abstract Factory

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Review

• What is the difference between aggregation and
  composition?
• Factory Method

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Dependencies

• A dependency exists between to classes (or other
  elements) if changes to the definition of one
  element may cause changes to the other
• Ideally we are considering changes to interface
• not as strong as an association relationship

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Dependencies

• An object of one class creates an object of
  another class

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Dependencies

• An object of one class sends a message to another
• but the sending object is not responsible for
  keeping track of the receiving object (which
  would be association)

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Dependencies

• one class mentions another as a parameter to an
  operation

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Parameterized Class

• Classes hide and manipulate data/objects
• Often we want to specify the way in which
  data/objects are stored and manipulated without
  actually specifying the actual type of the
  data/objects
• Parameterized classes allow types to be a
  parameters in the class or function definitions

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Parameterized Class

• Used mainly for containers
• sometimes for other novel implementations
• Also known as
• Templates in C
• Generics in Ada

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Example

• Stacks are a general concept
• We might want to have stacks of int, char,
  complex, or some other user defined objects
• We would like to describe stacks in terms of some
  unknown type (say T), a type parameter, and
  provide an actual real type when we need a stack.

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Example

• Here T is a type parameter

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Binding Relationship

• Sometimes called instantiation
• Note this is not the same as object
  instantiation
• A new class created by specifying an actual type
  is called a bound element
• Binding is a kind of dependency relationship
  between a class which is a bound element and a
  parameterized class

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Example

• Here complex is an actual type which is
  substituted for the type parameter T

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Java Example
interface ListltEgt void add(E x) IteratorltEgt
iterator() class LinkedListltEgt implements
ListltEgt // implementation class
AnotherClass LinkedListltstringgt strList new
LinkedListltstringgt() someMethod()
strList.add(Hello, World!) string
returnStr strList.getHead()
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Parameterized Classes vs. Generalization

• A bound element (instantiated class) is a
  kind-of the parameterized class
• But this is not Generalization
• Binding merely restricts the type(s) used but the
  interface remains the same
• Instantiation provides no mechanism for adding
  new functionality (state or interface)

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Parameterized Classes and Generalization

• Note Alternate notation for binding

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Abstract Factory Pattern

• Provide an interface for creating families of
  related or dependent objects without specifying
  their concrete classes.

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Teaching Points

• Dependency
• Parameterized Classes
• Abstract Factory