Object-Oriented Principles and Implementations

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Object-Oriented Principles and Implementations
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Agenda

• Evolution of software
• OO software elements
• Object instantiation
• Run-time environment
• Mapping to real-world
• Object lifecycle

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Evolution of Software

• Remember form, function, style
• data, logic, paradigm
• state, behavior, style
• state collection of all data values (e.g., at
  this time)
• Paradigms
• monolithic
• modular
• functional gt ADTs gt OO gt componentware??

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OO Software Elements Objects

• real life view
• person, place, thing, concept, event
• OO view instantiation of a class
• storage view
• area of storage allocated to hold both the data
  for this object and its superclasses (its
  state), including all hidden data, and
  references to executable code the object can
  invoke/call
• multiple objects of same class share executable
  code and static variables

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OO Software Elements Classes

• real life view
• template, factory, pattern, IRS tax form
• OO view
• abstraction of a kind of object
• definition of services (methods) that can be
  performed
• storage view
• one copy of all static variables per class, plus
  the storage to hold one copy of all method code,
  plus some overhead
• no storage for object/instance state

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Local Object Instantiation

• two storage areas
• local reference to object
• local storage for objects state and methods
• new is normally used
• allocates local memory
• object storage is released when
• object is no longer in use and garbage collector
  runs
• program exits

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Local Object Storage

• Declaration Temperature outside_temp

outside_temp (2AF0)
(object reference is null)

• Storage allocation
• outside_temp new Temperature(32.0)

2AF0
3C320
3C328
3C32C
3C330
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Two Local Objects of Same Class
Temperature outside_temp
new Temperature(32.0)
Temperature water_temp
new Temperature(212.0)
2AF0
3C320
3C328
2AF4
3C32C
3C330
3C340
3C348
3C34C
3C350
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Shallow Object Copy
Temperature outside_temp
new Temperature(32.0)
Temperature water_temp
new Temperature(212.0)
Temperature a_temp
outside_temp
2AF0
3C320
3C328
2AF4
3C32C
2AF8
3C330
3C340
3C348
3C34C
3C350
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Remote Object Instantiation

• four storage areas
• local reference to object (actually, for
  stub/proxy)
• local storage for proxy and parameters
• remote storage for remote proxy, parameters and
  return value/exception info
• remote storage for objects state and methods
• new is not used
• remote proxy causes new for remote object
• foundation for most of EA infrastructure

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Run-Time Environment

• loads/unloads classes
• schedules threads
• allocates storage
• runs garbage collection
• interfaces with operating system

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Mapping to Real World

• enabled by from exposed state to exposed
  interface
• handling large problems desirable
  characteristics
• object-orientations part in solving problems

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Desirable CharacteristicsModularity

• isolates functionality
• serves as unit of decomposition
• can be assigned as a work item
• allows for a standard interface
• speeds time to market by aiding problem
  partitioning
• helps with understandability
• thus maintainability and extensibility

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Desirable CharacteristicsEncapsulation

• simplifies interface
• promotes consistency
• controls access
• allows underlying data representation to change
• aids maintainability

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Desirable CharacteristicsAbstraction

• allows easier identification of reusable parts
• saves work effort by closer mapping to problem
• improves reliability by supporting reuse
• makes changes easier to propagate
• central, inherited concepts
• saves development time by inheriting capability

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Desirable CharacteristicsReuse

• saves time
• allows for purchase vs. roll-your-own
• allows reaping benefits of accumulated experience
  from reused entity

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Object Orientation and the Real World

• Classes are generalizations and abstractions of
  real-world objects and their behaviors
• examples business concepts (Order), people
  (User), service provider (DatabaseInterface)
• Objects are unique and have an identity
• examples
• order451 (instance of Order)
• SaleClerkJane Doe (instance of User)
• inventory_db (instance of DatabaseInterface)

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Bean Object Activation Activities

• creation
• create bean object but defer assigning storage
  for state
• passivation
• disassociate bean object from its state and save
  the state
• removes bean object from memory
• activation
• loads bean object into memory
• restores state and associates with bean object
• removal
• remove bean object from memory