Object Oriented Programming Development Polymorphism I

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Object Oriented ProgrammingDevelopment -
Polymorphism I

• By
• Marc Conrad Rob Manton
• University of Luton
• Email
• Marc.Conrad_at_luton.ac.uk
• Rob.Manton_at_luton.ac.uk
• Room
• D104

2
Module Outline

• Inheritance
• Aggregation
• Polymorphism
• Multifile Development

• Introduction
• Non object oriented basics
• Classes

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Todays lecture

• Polymorphism I
• method overloading
• operator overloading

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The Meaning of the word.

• From the Greek
• Polus Morphe Polumorphos
• (many ) (shape/form)
• The English word "polymorphe" dates from the 19th
  century and was applied to different animal forms
  arising in the the same species.

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The Meaning of the word.

• In object-oriented computing it means different
  forms of data being handled by the same type of
  process.
• Example The operator has a different meaning
  in the expression 2 3 (add two integers) than
  in 1.7 3.3 (add two floating point numbers)

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Types of Polymorphism

• In Object Oriented Programming there are three
  types of polymorphism
• method overloading, with the special and
  important case of operator overloading
• method overriding
• run-time polymorphism

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Types of Polymorphism

• In Object Oriented Programming there are three
  types of polymorphism
• method overloading, with the special and
  important case of operator overloading
• method overriding
• run-time polymorphism

• Method overloading can also be applied in
  non-object oriented contexts and refers both to
  functions and methods.

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Types of Polymorphism

• Method overriding and run-time polymorphism are
  specific to inheritance hierarchies and object
  oriented programming
• (more about this next week..)

• In Object Oriented Programming there are three
  types of polymorphism
• method overloading, with the special and
  important case of operator overloading
• method overriding
• run-time polymorphism

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Types of Polymorphism

• In Object Oriented Programming there are three
  types of polymorphism
• method overloading, with the special and
  important case of operator overloading
• method overriding
• run-time polymorphism

• Run-time polymorphism, also called dynamic
  binding, or late binding is often considered as
  the object oriented feature of C.

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Method Function Overloading

• Overloading a function simply means, that a
  function is not only defined by its name but by
  its name and parameter types.
• The following functions are different in C
• int makeBreakfast(int i, int k)
• void makeBreakfast(Creature who)
• float makeBreakfast()

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Example The Creature class

• class Creature
• private
• int yearOfBirth
• public
• void setYearOfBirth(int year)
• yearOfBirth year
• void setYearOfBirth(Creature other)
• yearOfBirth other.yearOfBirth
• int getYearOfBirth()
• return yearOfBirth

born1997
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Example The Creature class

• class Creature
• private
• int yearOfBirth
• public
• void setYearOfBirth(int year)
• yearOfBirth year
• void setYearOfBirth(Creature other)
• yearOfBirth other.yearOfBirth
• int getYearOfBirth()
• return yearOfBirth

These two methods are different.
born1997
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Example The Creature class
These two methods are different because they have
different argument types.

• class Creature
• private
• int yearOfBirth
• public
• void setYearOfBirth(int year)
• yearOfBirth year
• void setYearOfBirth(Creature other)
• yearOfBirth other.yearOfBirth
• int getYearOfBirth()
• return yearOfBirth

born1997
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Operator Overloading - Motivation

• Question How many function calls are involved in
  the following statement?
• a 2 3

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Operator Overloading - Motivation

• Question How many function calls are involved in
  the following statement?
• a 2 3
• There are two functions implicitly involved
  and .
• Look at this statement as
• assign(a, add(2,3))

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Operator Overloading

• So, operators as , -, , ltlt, , etc. can be seen
  as functions as well. That means we can
  overload operators.
• The C syntax uses function names prefixed
  with operator for overloading operators.

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Overloading Operators - Example

• A Sandwich filling.
• may contain bacon (yes/no).
• a fraction of a lettuce-leaf.
• a number of tomato slices.

• class BLT
• public
• bool bacon
• float lettuce
• int tomatoes
• // Constructor
• BLT(bool b, float l, int t)
• // (more code)

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Overloading Operators - Example

• BLT filling1(true,0.5,2)
• BLT filling2(false,0.2,0)
• ...
• BLT filling3 filling1 filling2
• ...
• / Should give a filling with bacon, 0.7 lettuce
  and 2 tomatoes/

• class BLT
• public
• bool bacon
• float lettuce
• int tomatoes
• // Constructor
• BLT(bool b, float l, int t)
• // (more code)

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Overloading Operators - Example

• BLT filling1(true,0.5,2)
• BLT filling2(false,0.2,0)
• BLT filling3 filling1 filling2
• ...
• / Should give a filling with 3 bacon slices,
  0.7 lettuce and 2 tomatoes /

• class BLT
• public
• bool bacon
• float lettuce
• int tomatoes
• // Constructor
• BLT(bool b, float l, int t)
• // (more code)

This is the operator we want to overload
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Operator Overloading - Example
If we try adding the two objects together at the
moment we get the expected error message
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Overloading Operators - Example

• // The C Syntax
• BLT operator(BLT x, BLT y)
• bool b x.bacon y.bacon
• float l x.lettuce y.lettuce
• int t x.tomatoes y.tomatoes
• BLT result(b,l,t)
• return result

• class BLT
• public
• bool bacon
• float lettuce
• int tomatoes
• // Constructor
• BLT(bool b, float l, int t)
• // (more code)

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Overloading Operators - Example
operator overloaded to accept two BLT objects
as arguments.
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Overloading Operators - Example
Note return type is BLT
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Overloading Operators - Example
Because overloaded operator returns a BLT
object, this works!
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Overloading Operators - Example

• void operator(BLT x, BLT y)
• bool bacon ( x.get_bacon()
• float lettuce x.get_lettuce()
• int tomsx.get_tomato_slices()
• x.set_bacon(bacon)
• x.set_lettuce(lettuce)
• x.set_tomato_slices(toms)

Where an operator like actually needs to
change the first operand, we need to use the
(call by reference) syntax
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Operator Overloading

• Operators can also be overloaded as methods, e.g.
  the operator
• class BLT
• //
• BLT operator(BLT other)
• bacon ( bacon other.bacon)
• tomatoes other.tomatoes
• lettuce other.lettuce
• //

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Operator Overloading
operator overloaded to accept one extra BLT
object as an argument -note void return type
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Operator Overloading
The const keyword indicates to the compiler that
you are not going to change the other BLT object
in any way
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Operator Overloading
BLT filling1(true,0.5,2) BLT filling2(false,0.2,0
) filling1 filling2 ... /
Should give a filling with bacon, 0.7 lettuce
and 2 tomatoes/

• Operators can also be overloaded as methods, e.g.
  the operator
• class BLT
• //
• BLT operator(BLT other)
• bacon ( bacon other.bacon)
• tomatoes other.tomatoes
• lettuce other.lettuce
• //

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Operator Overloading

• Operators can also have other types as parameter
  
• class BLT
• //
• BLT operator(int factor)
• tomatoes factor
• lettuce factor
• //

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Operator Overloading
BLT filling1(false,0.5,2) filling1
2 ... / Should give a filling with no
bacon, 1 lettuce and 4 tomatoes /

• Operators can also have other types as
  parameters
• class BLT
• //
• BLT operator(int factor)
• tomatoes factor
• lettuce factor
• //

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Operator Overloading

• The following operators can be overloaded
• new, delete, , -, , /, , , , , , !, , lt,
  gt, , -, , /, , , , , ltlt, gtgt, gtgt,
  ltlt, , !, lt, gt, , , , --, , , -gt. -gt,
  (),
• Note that "" has already a default behaviour.
  When "overloaded" it will be in fact overridden.

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Operator Overloading - Interesting Observation

• cout ltlt Hello World\n

Overloaded ltlt operator
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Operator Overloading - Interesting Observation

The ltlt operator is overloaded to take a BLT
object as an argument
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Operator Overloading - Interesting Observation

• BLT myFilling(1,0.5,4)
• cout ltlt myFilling ltlt endl

Now we can perform class-specific output using
the standard ltlt syntax!
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Operator Overloading - Summary

• Operators may be overloaded to work with user
  defined data types (objects).
• The syntax for overloading involves the
  'operator' keyword and the operator.
• Note In a good design it is important, that the
  normal meanings of operators are not distorted
  (don't subtract with a operator)