rickers@drexel.UUCP (Rick Wargo) (12/23/87)
Netlanders...
Here is a quick guide that I had put together for a just-for-the-heck-of-it
Concepts of Objected-Oriented Programming Languages Course. I have not been
reading the news lately, I hope this is not too out of date. I have had many
requests for this in the past, but I have not been able to find it until today.
I hope that it self explanatory (it should be 8-).
It is structured not by topic, but by order of reference. I have found
these references valuable and well worth reading.
Rickers
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Concepts of Object-Oriented Programming
- from Elements Of Object-Oriented Programming
Elements Of Object-Oriented Programming
Geoffrey Pascoe
of DoD Computing Systems Research Division (MD)
Byte Magazine
Volume 11 Number 8 (August 1986) pages 139-144
- information hiding
- important for ensuring reliability fo software
- reduces inter-dependencies
- state of a software module contained in private variables
accessible from only within the scope of the module
- most languages support information hiding
example
static variables in functions in C
- data abstraction
- could be considered a way of using information hiding
- programmer defines an abstract data type
consists of an internal representation
a set of routines to access and manipulate the data
- dynamic binding
- poly-morphism
the same message can elicit a different response depending on the receiver
done at runtime
no need to modify existing code
- inheritance
- sub/super classing
- automatic storage management
- better known as garbage collection
- should qualify as fifth important element
- from ObjC Reference Manual
Objective C Reference Manual
1984 - PPI
Sandy Hook, CT
- a computational metaphor
operands replaced by objects (private data - encapsulated
- operator/operand model vs. object message model
- operator/operand model
similar to a switchboard concept. user must select which
operators to match each specific operand.
plugs are the set of operators
sockets are the addressable operands
- message/object model
no interdependencies
user is responsible for knowing and respecting all data
type assumptions.
responsibilities
user is responsible for selecting objects and telling them
what to do. objects are responsible for deciding how to
implement each command.
- binding
- user-specified binding
example languages - C, Pascal, Fortran
seperate routines to manipulate independent types
ex. prnPoint(point) ; prnRectangle(rect)
- static binding
example languages - Simula, Ada, CLU
programmer specifies abstract name of operation, compiler
differentiates at compile time.
example: print(point); print(rect)
- examples
container
if want to add objects, need to update all switch
statements
for all elements in (variant) array
print each one
need to use switch statement depending upon data
type of aray element.
example of dynamic binding
not reusable because all switch statements need to be
updated when a new data type is added.
- new basic concepts
- object
set of organized data/operations
- class
a description of whatUs shared by a group of similar objects
inheritance
- method
how an object will perform one of its operations
"a functional call"
- message
a request for an object to cayy out a method
- operations done by objects, not to objects
- a message expression
- receiver
identifies the object that will receive the message
- selector
identifies the message being sent to the receiver
- arguments
same as functional arguments
- keywords
unary
- factory objects
- main function
creating new unitialized objects
- parts of an object
- shared part
describes what is similar among all objects of this class
methods are shared
template (or structure) describing private data of each
instance
called the class structure
- private part
actual values held in each instance
- methods (or behaviors)
- may have format arguments
- can return a value
- names need not be unique across classes
- not called directly by name, but by a dispatch table
- can access private data of it receiver
- self
- available automatically to every method
- identifies the object receiving the message
- inheritance
- a technique for organizing information into specialization/generalization hierarches
- class description
specifies only how the class being defined differs from some
existing class (the suoerclass)
- root class
a generic, non-specialized class at the top of the hierarchy
tree, usually specified by "Object."
- code reusability
- multiple inheritence
"toy truck" example
should it be a member of the "toy" class?
should it be a member of the "truck" class?
- from Smalltalk-80 - The Interactive Programming Environment
Smalltalk-80 - The Interactive Programming Environment
"The Orange Book" as opposed to "The Blue Book"
Adele Goldberg - Xerox PARK
Addison-Wesley Publishing Co. 1984
- Adele Goldberg
- group manager at PARC (Software Concepts Group)
- responsible for documenting the system
- Larry Tesler
- first introduced the system browser
enriched by Dan Ingalls
- General system configuration for Smalltalk
- high-resolution bitmapped display screen
- a typewriter keyboard
- a pointing device
- objects
- a uniform representation of information
- has "private memory"
can only be manipulated by the operations in the objects interface
- capability to manipulate stored info
- capability to carry out some activity
- objects and messages
- encourages modular design
- implementation of one object cannot depend on internals of another
only on how they respond to messages
- used to implement the entire programming environment
- used to represent:
numbers
lists
text strings
dictionaries
spatial locations
areas
text editors
processes
compilers
debuggers
and all other system components
- classes
- objects that respond to the same messages in the same way
- objects in a group are called instances of the class
- ability to create a subclass of an existing class
adds new functionality
adds new private memory
modifies or prohibits existing functionality
- advantages of Object-Oriented Programming
- information known privately to an object is protected
can only be accessed by methods of the object
- a simple and expressive model for the relationship of parts & wholes via classes and inheritance
- objects support modularity
- interaction is same within all levels of complexity
- message expressions
- represent interactions between components of a Smalltalk system
- describe receiver, selector and possible arguments
- cascaded messages
- multiple messages to the same object
- method
- describes how an object will perform one of its operations
- class descriptions
- a class name
- the superclass of the class
- a declaration of the variables to the instances
- the methods used by instances to respond to messages
- kinds of variables accessed by methods
- instance variables
exist for the lifetime of the object
represent the current state of an object
- temporary variables
created for specific activity
available only for durations of that activity
represents the transitory state necessary to execute a method
- class variables
shared by all instances of a class
- global variables
shared by all instances of all classes
- pool variables
shared by the instances of a subset of classes in the system
- metaclass
- a class whose instances are themselves classes
- analagous to a factory object
- method determination
- message is searched for in the methods of the receivers class
- if not found, searched for in that classes superclass, etc.
- if not found (stops at root class (Object))
that class generates the message doesNotUnderstand: (selector)
- self
search own methods first for message
- super
search superclass methods first for the message
- programming involves
- specification of one or more class descriptions
- creating instances of the class
- sequencing messages to the instances
- keyword
- an identifier with a trailing colon (:)
- keyword message
- a message with one or more arguments whose selector is made up of one or more keywords
- from Software ICUs
Software ICUs
Lamar Ledbetter and Brad Cox of PPI
Byte Magazine
Volume 10 Number 6 (June 1985) pages 307-316
- Software IC
- a reusable software component
- encapsulation
- defines a data structure and a group of procedures for accessing it
- users access the data structure only through standardized interfaces
carefully documented
controlled
- hardware world achieves a high amount of reusability
- through the development of standards
- operator/operand versus message/object
- Hardware ICUs
- custom circuits from individual components
- reusability
possible because chip packaging makes hardware environment independent of the detailed workings of the chip
high degree of reusability through standards
dynamic binding and encapsulation are at the root of reusability
- division of responsibility
defined and enforced through messaging
- hardware components delivered in un-modifiable form
- a hardware designer never starts from scratch
- Software ICUs
- directly support the concept of rapid prototyping
- direct relationships to Hardware ICUs ideas
- from A Taste of Smalltalk
A Taste Of Smalltalk
Ted Kaehler (Xerox PARC & Apple)
Dave Patterson (University of CA, Berkeley)
1986 W.W. Norton & Co., Inc.
- Smalltalk-80 is
- a civilized programming environment
- the premier OOPL
- uniform treatment of different kinds of info
- similar to Lisp in this aspect
- examples
text
graphics
symbols
numbers
- Smalltalk roots
- where developed
Developed in the Learning Research Group at XeroxUs Palo
Alto Research Center (PARC) in the early 1970Us.
- major ideas belong to Alan Kay
also
Simula
Lisp
SketchPad
- early implementation by Dan Ingalls
first person to write code for
multiple overlapping windows
opaque pop-up menus
BitBlt
- Smalltalk-80 is a "presentable" version of Smalltalk-76
- license 2 is the standard system (active)
- license 1 is older (available from Apple)
- methods
- a Smalltalk procedure or subroutine
- can have arguments
message selectors
a method is a procedure, a selector is the procedure name
use selector to find right method to execute
- a description of one of an objectUs operations
not an action
- objects
- a package of data and procedures that belong together
- like a Pascal record, but much richer
- self
a way of referring to the object
used for recursion
- all return an object as its result
default is self
- modular code
- well established in computer science
- alone does not make a program Object-Oriented
- from Object-Oriented Programming for the Macintosh
Object-Oriented Programming for the Macintosh
Kurt Schmucker of PPI
Hayden Book Company 1986
- effects of the Object-Oriented approach
- significant reductions in
development time
size of source code
- notions central to Object-Oriented programming
- objects
- classes
- methods
- inheritance
- the classes protocol
- set of messages of a class
- a reference
- an objects address
- methods
- call by desire
message sender need not worry about anything
just sends what it desires the object to do
- a root class
- the place for hierarchy to start
- method overhead
- when implemented in a sufficiently clever manner
- as small as 1.75 times that of the standard procedure call
- time penalty less than 10 percent
- hybrid languages
most so-called objected-oriented languages fall into this class.
Smalltalk is a true OOL
- allow to choose between an Object-Oriented approach and a conventional procedural one
- make use of existing libraries
- less of a culture shock
- learned in less time
- allow to choose between a method and subroutine call
- methods
- private methods
used only by the class designer
- basic methods
very rarely (or never) overridden
- class methods
instance methods of the class (factory)
- class instance variables
- rarely used
- metaclass
- a classUs class
- multiple inheritance
- ability to be a subclass of more than one class
- very powerful
- examples
houseboat
a subclass of the classes "house" and "boat"
is it a house or a boat?
squares
a subclass of the classes "rects" and "rhombi"
circular queues
a subclass of the classes "queues" and "linked lists"
- primary immediate ancestor class
inherits most from this class
on conflict of methods, inherits from this class
- searching for method now more complex
tree becomes a graph (acyclic)
more difficult and time consuming
- existing languages that support multple inheritance
Smalltalk
Object Logo
available for $79.95 from Coral Software
ExperCommon LISP
- unique instance methods
- provide storage of a method in the object itself
- not stored in its classUs message and method table
- Object Logo demonstrates this
- from The C++ Programming Language
The C++ Programming Language
Bjarne Stroustrup
AT&T Bell Labs
Murray Hill, NJ
Addison Wesley Publishing Company 1986
- C++
- is a superset of the C programming language
- originally called C with classes
- data abstraction
- partition an application into manageable pieces
done by defining new data types that closely match the concepts of the application
- classes
- a user defined type
- provides
data-hiding
guaranteed initialization of data
implicit type conversion for user defined types
dynamic typing
user controlled memory management
mechanism for overloading operators
- features not related to classes
- symbolic constants
- inline substitution of functions
- default function arguments
- overloaded function names
- free store management operators
- a reference type
- operator overloading
- same operator has different meanings in different contexts
- constructors
- class initializers
- destructors
- class cleaner-uppers
- derived classes
- inheritance
- friends
- lets a function be the friend of two or more classes
- virtual functions
- defined in a derived class
- overloaded function names
- a certain routine is called depending upon function arguments
- self reference is accomplished via the variable "this"
- auto-initialization is accomplished via constructors
- cleanup is done via destructors
- from Usenet discussion, C++
Bjarne Stroustrup article
date ????
- is a better C
- argument type checking and type conversion
- free store operators (new & delete)
- scoped and typed constants
- inline functions (function semantics with macro efficiency)
- supports data abstraction
- data hiding
- member functions (operations on objects of a class)
- constructors (optional guaranteed initialization)
- destructors (optional implicit cleanup)
- operator overloading (+ * / etc; and also () [] and =)
- user defined type coercion
- references
- supports Object-Oriented programming
- (single) inheritance (sub/super classes)
- virtual functions (a bit like Smalltalk methods, but fast)