More to Class - Lecture notes 5 PDF

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Summary

Programming Technique 2: More to Classes Static Member Variable • Static member variable: shared by all the data in the class, it is NOT stored in an object data • o it is stored before any data is created o must declare outside the class o private: o static int objectCount; // inside class (no init...

Description

Programming Technique 2: More to Classes Static Member Variable •

Static member variable: shared by all the data in the class, it is NOT stored in an object data

•

o

it is stored before any data is created

o

must declare outside the class

o

private:

o

static int objectCount; // inside class (no initialization)

o

int Tree::objectCount = 0; //outside class (initialize to 0)

Normally static member variable is used to count the number of functions being called

•

we can set static variable to be incremented in constructor so that every time an object is created, the number will increase by 1

•

Static member function cannot access any non-static member data in class

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When static function is created, it is called before any instances of classes are defined

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Friend= function / class that is not member of the class but can access the private members of that class

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Friend can be stand-alone function or member function of other class / entire another class o

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Format :: friend ReturnType FunctionName ( ParameterTypeList )

Copy Constructor : called when an object is initialized with another object’s data. o

format almost same as normal constructor but it has reference object

o

ex:

o

StudentTestScores( const StudentTestScores &obj)

o

{ studentName = obj.studentName; }

o

put const because copy constructor copy argument data only, cannot change data

o

put reference to prevent the copy constructor from calling itself infinite time

o

copy constructor is done so that the data in obj.studentName wont destroy/ corrupt the data in copy constructor studentName

•

•

overloaded operator: o

=

o

+=

o

-+

o

/=

postfix ++ operator has dummy parameter : o

FeetInches FeetInches::operator++(int)

o

the one in the bracket is dummy parameter, computer will know this is postfix when they see it

•

For prefix, the bracket won’t have variable : o

•

•

FeetInches FeetInches::operator++( )

prefix : n=++m o

increment m first, then assign

o

if initially n and m =0, then this code will produce n=1, m=1

postfix : n=m++ o

assign m first then increment m

o

this code will produce n=0, m=1

•

To convert an int type to double or etc. (double d=int c)

•

Aggregation: used when a class need to access another class's instance

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default constructor → initialize the data to 0

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constructor→ set each data to its type

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Diagram o

aggregation =white diamond shape

o

composition =black diamond shape

•

Composition cannot live on its own, once the composed class collapse, it dies too

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Aggregation can live on its own, once the aggregated class collapse, it still can function

•

Aggregation use pointer * object, call function by '→ ' o

at the main function need to dynamically allocate the pointer

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ex: Student *prefect=new Student ("Ali"); //Ali is stored in prefect data

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Composition didn’t use pointer, just use object straight away call function

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Association use pointer *object also but just normal '=' assign, didn’t use ' → '...