OOP Class Lawrence D

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OOP ClassLawrence DAntonio

• Lecture 3
• An Overview of C

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Classes/Objects

• Basic unit of OOPL
• Autonomous entities
• State, behavior, identity
• Data encapsulation
• Encapsulation of responsibilities
• Information hiding
• Message passing
• Exception handling

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Object Organization

• Inheritance (Single and multiple)
• Dynamic binding
• Generalization/Specialization
• Abstraction
• Has-a versus is-a relationship
• Uses relationship
• Polymorphism/ Virtual functions

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Polymorphism

• Virtual functions
• Overloading
• Type conversions
• Templates

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Generic programming

• Templates
• STL
• Traits
• Metaprogramming
• Boost library
• Programming with concepts

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Typing

• Statically typed. Variables must be declared
  before used. Exceptions casts, unions, temporary
  objects.
• Weakly typed (?). Variables are not bound to a
  specific data type.
• Type conversions
• Subtyping

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Code Reuse

• Parametric polymorphism
• Subtyping polymorphism
• Composition
• Patterns

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What is a class?

• A class is a set of objects sharing common
  features.
• A class defines an objects attributes and
  behavior. Methods are provided to act on an
  object and to pass messages between objects.
• A class is the basic unit of abstraction.
• A class is the basic unit of modularity.
• A class can be concrete or abstract.

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What is an object?

• An object is an instance of a class.
• An object has state, behavior, identity.

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What is an object?

• Coad-Yourdon
• An abstraction of something in a problem domain,
  reflecting the capabilities of the system to keep
  information about it, interact with it, or both
  an encapsulation of attribute values and their
  exclusive services.

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What is an object?

• OMG
• An object is a thing. It is created as the
  instance of an object type. Each object has a
  unique identity that is distinct from and
  independent of any of its characteristics. Each
  object offers one or more operations.

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What is an object?

• Firesmith
• An object is defined as a software abstraction
  that models all relevant aspects of a single
  tangible or conceptual entity or thing from the
  application domain or solution space. An object
  is one of the primary entities in an
  object-oriented application, typically
  corresponds to a software module, and consists of
  a set of related attribute types, messages,
  exceptions, operations, and optional component
  objects.

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What is an object?

• Booch
• From the perspective of human cognition, an
  object is any of the following
• A tangible and/or visible thing.
• Something that may be apprehended intellectually.
• Something toward which thought or action is
  directed.

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What is an object?

• Booch continued.
• An object has state, behavior, and identity the
  structure and behavior of similar objects are
  defined in their common class the terms instance
  and object are interchangeable.

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What is an object?

• Shlaer-Mellor
• An object is an abstraction of a set of
  real-world things such that
• All the things in the set have the same
  characteristic.
• All instances are subject to and conform to the
  same set of rules and policies.

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What is an object?

• Jacobson
• An object is characterized by a number of
  operations and a state which remembers the effect
  of these operations.

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What is encapsulation?

• Internal details of objects are concealed from
  the objects users (information hiding).
• Both data and implementation may be hidden. The
  object is a black box.
• Access to members is controlled through the class
  definition.
• The accessible part of a class is called its
  interface.

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Data encapsulation example

• class Clock
• private
• int hours // 1-12 private
• int minutes // 0-59
• public
• Clock(int h, int m)
• if (h lt 1 h gt 12)
• throw(Hours must be between 1 and
• 12?)
• if (m lt 0 m gt 59)
• throw(Minutes must be between 0 and
• 59?)
• h hours
• m minutes
• //...

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Class Invariants

• The above is an example of Programming by
  Contract.
• The class guarantees that
• These are called class invariants

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What is a method?

• A method is a member function that acts upon an
  object. A method is generally called for one
  object (exception static members).
• Commonly found methods are constructors,
  destructors, assignment, mutators, accessors.

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What is message passing?

• Messages are transfers of data or requests for
  another object to take an action.

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What is polymorphism?

• Different types of objects respond to the same
  message and use the appropriate method.
• Parametric polymorphism parametrizes the object
  type (e.g., a list class, where the type of
  object stored is parametrized).
• Subtype (or inclusion) polymorphism allows
  objects of a given type to be substituted for by
  objects of a subtype.

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What is inheritance?

• One class (derived/child) relies on the
  definition of another class (base/parent).
• Single vs. multiple inheritance
• A method of sharing code or sharing interface
  among classes.
• Language may define a class tree (with single
  root) Java, Smalltalk
• Language may define a class forest C

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What is typing?

• Static typing Data type determined at
  compile-time. Type must be declared.
• Dynamic typing Data type may be determined at
  run-time. Type need not be declared.
• Strong typing Variables are bound to a specific
  type.
• Weak typing A variables type may change.

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Varieties of typing

• Static and strong typing Java, Pascal, OCaml,
  Haskell
• Static and weak typing C/C
• Dynamic and strong typing Python
• Dynamic and weak typing PHP

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Dynamic typing example

• Python example
• class Cat def speak(self) print "meow!"
• class Dog def speak(self) print "woof!"
• class Bob def speak(self) print "hello world!"
• def command(pet) pet.speak()
• pets Cat(), Dog(), Bob()
• for pet in pets
• command(pet)

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Weak typing example

• var x 5
• var y "37"
• Print(x y)
• In Visual Basic this prints 42
• In JavaScript this prints 537

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What is exception handling?

• The mechanism used to report and recover from
  abnormal states.
• When an error is detected, execution is passed to
  a handler.