Methodology First and Language Second -A Way to Teach Object-Oriented Programming

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Methodology First and Language Second-A Way to
Teach Object-Oriented Programming

• Haibin Zhu, PhD
• Department of Computer Science and Mathematics
• Nipissing University, North Bay, Canada
• email haibinz_at_nipissingu.ca
• URL http//www. nipissingu.ca/faculty/haibinz

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Contents

• Introduction
• Six Steps to Introduce the Object-Oriented
  Programming
• Teaching inheritance in C
• Teaching Other Concepts in C
• Conclusion

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Introduction

• Object-oriented programming is required
• C is an OOPL used to teach OOP
• C is a flexible language that needs the
  instructor to guide the students to master C
  and OOP.
• It is a failure for both teaching and learning
  OOP with C that students know how to program in
  C but not in OOP.

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The Six Steps

• General Principles
• Object
• Class
• Instances
• Inheritance
• Metaclass

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Step 1

• Discuss fundamental principles of
  object-orientation with respect to conventional
  thinking
• Fundamental Principles
• Everything in the world is an object 4.
• Every system is composed of objects (certainly a
  system is also an object).
• The evolution and development of a system is
  caused by the interactions among the objects
  inside or outside the system.

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Step1(contd)

• Fundamental concepts
• Abstract and induction
• Concretion and Deduction
• Composition and Decomposition
• A class exercise
• Describe yourself.

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Step 2

• Introduce an object concept by observing the real
  world
• Everything is an object
• Object ltN, s, M, X gt, where
• N is an identification or name of an object
• s is a state or a body represented by a set of
  attributes
• M is a set of methods (also called services or
  operations) the object can perform and
• X is an interface that is a subset of the
  specifications of all the methods of the object.
• A class exercise
• Describe yourself by this expression

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Step 3

• Acquire the class concept by abstraction of many
  common objects
• Many objects with common properties form a class
• C ltN, D, M, Xgt, where
• N is an identification or a name of the class
• D is a space description for memory
• M is a set of the method definitions or
  implementations and
• X is a unified interface of all the objects of
  this class.
• A class exercise
• Describe a class you belong to.

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Step 4

• Introduce instantiation after the class concept
  is learned
• Every object has a class
• O lt N, C, S gt, where
• N is an identification or name of the object
• C is the objects class identified by the class
  identification or name and
• S is a body or an actual space whose values are
  called attributes, properties, or state.
• A class exercise
• Describe yourself as an instance of the class you
  described.

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Step 5

• Illustrate subclasses by adding more details to
  an existing class and superclasses by finding
  common things among several classes
• Specialization and generalization
• Cs ltN, C, D, M, X gt, where
• C denotes a set of superclasses identified by
  their identifications or names, and
• N, D, M, and X have the same meanings as those of
  C.
• A class exercise
• Describe a class that is a superclass of the
  class you belong to.

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Step 6

• (Optional) Discuss metaclasses to master
  completely the class and object concepts

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Teaching inheritance in C

• Classification-based view of inheritance
• Consistent structures, single inheritance and
  whole inheritance are inherent
• Code reuse-based view of inheritance
• Inconsistent structure, multiple inheritance and
  part inheritance reasonable

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Multiple inheritance

• Multiple inheritance
• Multiple inheritance brings about replicated
  inheritances, and programmers must use a
  "virtual" specifier to make it clear.
• Multiple inheritance and aggregation
• class Plane
• private
• Head head
• Engine engines4 //4 engines
• Wing wings2 //2 wings
• Tail tail
• public

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Inheritance and overloading
class d_class public b_class public
void display(B f )
coutltlt"d_class, f "ltltf.iltltendl
void play(B g )
coutltlt"d_class, g "ltltg.jltltendl
void main() b_class a d_class b a
new b_class() b new d_class() A
a1,a2 b-gtdisplay(a1) //(1) b-gtplay(a1) //(2
) b-gtplay(a2) //(3)

• include ltiostreamgt
• using namespace std
• class A
• public
• A()x 10, y 20
• int x,y
• class B public A
• public
• B()i 10, j 20
• int i,j
• class b_class
• public virtual void display(A a)
• coutltlt"b_class, a "ltlta.xltltendl
  
• void play(A b)
• coutltlt"b_class, b
  "ltltb.yltltendl

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Teaching Other Concepts in C

• Why constructors and destructors cannot be
  inherited
• Polymorphism and pointers
• About "this"
• Templates
• Friends
• Operator overloading
• Exception handling

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Constructors and destructors

• Constructors and destructors actually belong to
  the metaclass of a class.
• Why can the destructors of a base class not be
  defined without a virtual specifier? "
• A single polymorphic function (every class has
  only one destructor).
• "Virtual" specifiers shows that there are derived
  classes to be responsible for managing the spaces
  by themselves.

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Polymorphism and pointers

• A single name has different meanings.
• Without pointers, C would not support
  polymorphism.
• Fruit bag assumption
• An apple can be put in a bag of fruit, but a
  fruit cannot be put in a bag of apple."

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Templates

• One way to abstract
• Class templates are not classes, but
  parameterized classes from a class template can
  be used as ordinary classes
• Class templates are not classes, but they can be
  defined by inheriting an ordinary class and
• Class templates are not the same as the Smalltalk
  metaclasses.

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Friends

• Be careful to friends
• It increase the coupling among classes
• It is killing encapsulation
• Properties of friends
• Friend has no transitivity.
• Friend cannot be inherited.
• Friend has no reflexivity.

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Operator overloading

• Another way to name a member function
• For students, we suggest clear names
• const Time Timeoperator ( unsigned n )
• //...
• void main()
• Time a, b, c
• ab //(1)
• a.operator (b) //(2)

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Exception handling

• A pool assumption.
• Any time when the program tries (TRY) some
  message and
• encounters a defined exception, it throws (THROW)
  the exception object to the pool.
• After that, the program searches the pool and
  tries to catch (CATCH) an exception with its
  class identification the same as what is declared
  in the parameter list of the CATCH statement.
• If it catches such kind of exception, it does
  some exception handling operations. If not, it
  just follows the normal procedure.

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Conclusion

• Clear concepts and correct methodologies for
  students to learn OOP are very important
• C is a flexible object-oriented programming
  language, so that C programmers might use it in
  different ways.
• We must clarify which ways are good and which
  ways are bad.
• Need to mention This teaching methodology
  obtains better results for mature students than
  un-mature students!