1 159.234LECTURE 159.234 LECTURE Review for Finals 2009 x OOP

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159.234159.234 LECTURE LECTURE

Review for Finals 2009Review for Finals 2009

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OOP

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6 Questions

Final ExamFinal Exam

Q1. 20 marksQ2. 8 marksQ3. 12 marksQ4. 9 marksQ5. 12 marksQ6. 9 marks

Total = 70 marks

Different questions are worth differentnumber of marks.

87% - C++13% - Java

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EssentialsEssentials

Dynamic memory handling, pass by address, pass by reference.

String Stream processing, file handling

Application: Class design and analysis

Constructors, Destructors, data members, member functions

Access modifiers, static variables, virtual functions & destructors

Inheritance, Polymorphism, Function Templates, class Templates

STL: vector, list, map; Algorithms: find, sort, erase, insert

Java: Features removed from C++

Function Overloading, Operator Overloading

Java: inheritance, interfaces, parameter passing, garbage collection

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Memory Allocation, Deallocation in C++Memory Allocation, Deallocation in C++

Dynamic Memory HandlingDynamic Memory Handling

Memory leak.

new and delete operators

• This is important because mishandling pointers could easily cause your program to crash.

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5

Memory

POINTERS

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A pointer may be on the stack – but what it points to may be on the heap. Failing to free heap memory before exiting a function will leave memory on the heap that no longer has a pointer pointing to it.

This memory can never be recovered – it is called a memory leakmemory leak.

Get into the habit of always freeing memory. Even when the program exits.

• Only C++ Memory will be covered in the exam.

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C-Memory vs. C++ Memory

New 1-D Array allocation via function call

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int alloc1D(char **p, int elements){ (*p) = (char*) malloc(elements * sizeof(char));

if((*p) == NULL) return 0; else return 1; }

char *p; if(alloc1D(&p, 5)) { strcpy(p, "hello"); cout << "at main(): p = " << p << endl;}

free(p);

int new1D(char *&char *&p, int elements){

p = new charchar[elements];

if(p == NULL) return 0;else return 1;

}

char *pchar *p; if(new1D(p, 5)) { strcpy(p, "hello"); cout << "at main(): p = " << p << endl;}

delete [] p;

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int alloc2D(char ***p, int rows, int cols){

(*p) = (char **) malloc(rows * cols * sizeof(char *));

if((*p) == NULL) return 0;else return 1;

for(int i=0; i < rows; i++){ //(*p)[i] = (char *) malloc(cols * sizeof(char)); //OK *((*p)+i) = (char *) malloc(cols * sizeof(char)); //OK //(*p)+i) = (char *) malloc(cols * sizeof(char)); //ERROR!

if( *((*p)+i) == NULL) return 0; else return 1; }}

int new2D(char **&char **&p, int rows, int cols){

p = new char*char*[rows]; //array of pointers to char

if(p == NULL) return 0;else return 1;

for(int i=0; i < rows; i++){

p[i] = new charchar[cols]; //array of characters

if( p[i] == NULL) return 0; else return 1;

}}

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char **s;

if(alloc2D(&s,rows,cols)){ s[0] = "FILE"; s[1] = "EDIT"; s[2] = "QUIT"; for(int i=0; i < rows; i++){ cout << "s[" << i << "]= " << s[i] << endl; }}//------------------------------for(int i=0; i < rows; i++){ free(s[i]);}free(s);

char **s;char **s;

if(new2D(ss,rows,cols)){ strcpy(s[0] , "FILE"); strcpy(s[1] , "EDIT"); strcpy(s[2] , “QUIT"); for(int i=0; i < rows; i++){ cout << "s[" << i << "]= " << s[i] << endl; }}

//------------------------------// free-up memoryfor(int i=0; i < rows; i++){ delete [] s[i];}delete [] s;

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String Stream ProcessingString Stream Processing22

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Serves as a conduitconduit to an anonymous string which can be readwith the built-in ossoss.str() .str() function that is bound to the ossoss object

ostringstreamostringstream ossoss; int n = 44; float x = 3.14;

ossoss << "Hello!\t" << n << '\t' << x; string s = ossoss.str();.str();

cout << endl << s << endl;

Output String StreamOutput String Stream

Remember sprintf()?, how does it compare to this one?output_string_stream.cpp

#include <sstream>

11All extractions from ississ will come from the contents of buffer, as ifas ifit were an external fileit were an external file.

const string buffer = oss.str(); istringstreamistringstream ississ(buffer); string word; int m; float y; ississ >> word >> m >> y; s = ississ.str(); cout << endl << s << endl; cout << "word = " << word << endl; cout << "m = " << m << endl; cout << "y = " << y << endl;

Input String StreamInput String Stream

ississ is defined and bound to bufferbuffer

Contents of bufferbuffer can be accessedas elements of a string, or by formatted input through the ississobject.

Remember sscanf()?, how does it compare to this one?

input_string_stream.cpp

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#include <iostream>#include <fstream>#include <iomanip>#include <string>#include <sstream>using namespace std;int main(){

string s1("mydata.txt"); ifstream inin( s1.c_str() );

char buffer[1024]; while( inin.getline( buffer, 1024 ) ){

string stemp( buffer ); cout << "Line is:" << stemp << endl;

if( stemp[0] != '#' ){ stringstream stris( stemp ); double d1, d2; stris >> d1 >> d2; cout << d1 << "," << d2 << endl; } cout << endl; } inin.close(); return 0;}

Using string example• Input file:1.0 2.01.0 2.01.1 2.41.1 2.41.8 2.81.8 2.8##1.34 2.991.34 2.991.4 8.991.4 8.99

• Example Output:Line is:1.0 2.0Line is:1.0 2.01,21,2

Line is:1.1 2.4Line is:1.1 2.41.1,2.41.1,2.4

Line is:1.8 2.8Line is:1.8 2.81.8,2.81.8,2.8

Line is:#1.34 2.99Line is:#1.34 2.99

Line is:1.4 8.99Line is:1.4 8.991.4,8.991.4,8.99

open a file

Read one line of text, if there’s any available

close file

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#include <iostream>#include <fstream>#include <iomanip>#include <string>#include <sstream>using namespace std;int main(){

string s1("mydata.txt"); ifstream in( s1.c_str() );

char buffer[1024]; while( in.getline( buffer, 1024 ) ){

string stemp( buffer ); cout << "Line is:" << stemp << endl;

if( stemp[0] != '#' ){ stringstream stris( stemp ); double d1, d2; stris >> d1 >> d2; cout << d1 << "," << d2 << endl; } cout << endl; } in.close(); return 0;}

int main(){ string s1("mydata.txt"); ifstream in( s1.c_str() );

string buffer; while(getline( in, buffer ) ) {

cout << "Line is:" << buffer << endl;

if( buffer[0] != '#' ){ istringstream stris( buffer ); double d1, d2; stris >> d1 >> d2; cout << "data: " << d1 << "," << d2 << endl; } cout << endl; } in.close(); return 0;}

File_stringstream2.cpp

Alternatively: (no C-style char*)

Tank GameTank Game

ApplicationApplication

Designed to allow the students to apply everything they’ve learned about OOP. This also helps the students to realise how important and effective OOP is in simplifying the development of the game.

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Try to imagine re-writing the codes you have submitted into its corresponding non-OOP form. How much more difficult the codes would turn out?

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Tank GameTank Game

ApplicationApplication

See Lecture 16-Developing the Tank Game

World-to-Device coordinates representation

Using STL to implement the bombs with shrapnels

The sophistication of Physics were abstracted, encapsulated and injected using classes.

You should be able to describe the concept at least and come up with a class implementation (no need to memorize formulas).

How to implement a vector of bombs?

Interaction between classes: Tank, bomb, etc.

Inheritance, polymorphism, friend classes & functions

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See spikes*.cpp

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Transformation Equations

WORLD-to-DEVICE COORDINATES

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1280 x 1024 pixels

100,000,000 miles x 500,000 miles

World System of Coordinates Device System of Coordinates

+x

+y+x

+y0

0

(Xworld,Yworld)(XDevice,YDevice)

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World-to-Device Coordinates

TRANSFORMATION EQUATIONS

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12

12

XX

XX

worldBoundworldBound

ddeviceBounddeviceBounxSlope

11*tx_intercep XX WorldBoundXslopedDeviceBoun

tx_intercep* XX WorldXslopeDevice

• You don’t need to memorize the equations to prepare for the exam.

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Data Structures, data members

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outputs: x, y (device coordinates) - int int

Inputs: x, y (World coordinates) - double double BoundaryType WorldBound; BoundaryType DevBound;

double xSlope, xInt; double ySlope, yInt;

Does not change too often, only during initialisation and after zooming-in / zooming-out.

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Data Structures, data members

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class Transform{...private:

BoundaryType WorldBound;BoundaryType DevBound;

double xSlope, xInt;double ySlope, yInt;

};

typedef struct { double x1,y1,x2,y2;} BoundaryType;

const double g = 9.8;

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Projectile Motion

PHYSICS EQUATIONS

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where g = 9.8 m/sec.2 pull of gravity

Vo in m/sec. initial velocity

t in sec. time

tVox *cos*

tVogty *sin*2

1 2

Modifying timetime will allow you tocalculate the next xx & yy coordinatesof the object.

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(Non-OOP) (Non-OOP) Projectile Motion

PUTTING THE PIECES TOGETHER (non-OOP)

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// initGraphics here// initBoundaries here t=0.0; while(t < tf) { cleardevice(); setcolor(RED); circle (xDev(x(t, Vo, Theta)),yDev(y(t, Vo, Theta)), 12); t=t+tinc;

}

x() - implements a Physics Equation for x-coordinate calculation

xDev() - World-to-Device Transformation Function

//circle(x, y, radius)

class TransformTransform{

public:

//constructor

TransformTransform(BoundaryType WBound, BoundaryType DBound) :: WorldBound(WBound), DevBound(DBound) {

//calculate slope and intercept//calculate slope and intercept

if((WorldBound.x2-WorldBound.x1) == 0)

xSlope = (DevBound.x2-DevBound.x1)/(WorldBound.x2- WorldBound.x1+.001);

else

xSlope = (DevBound.x2-DevBound.x1)/(WorldBound.x2-WorldBound.x1);

xInt = DevBound.x1-xSlope*WorldBound.x1;

//....and so on...//....and so on...

}

int xDevxDev(double xWorld) const {return (int)ceil(xSlope*xWorld+xInt); } //from world to device //from world to device

...

private:

BoundaryType WorldBound, DevBound;

//...and so on...//...and so on...

};

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Slope and intercept values need to be calculated before the transformation from world to device could be performed.

devicedevice

//Instantiation

Transform tfmtfm(WBound, DBound);

//passing the object as an argument to the drawing methods

tank.draw(tfmtfm);

//draw function formal parameter definition

void Tank::draw(const Transform & tt) {

//...implementation here

fillellipse(t.xDev( t.xDev( headX )), t.yDev( t.yDev( headY )) …);

}

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Only one instance is necessary for all animated objects in the game!

Passed as a reference to a constant

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TemplatesTemplates


Operator overloading

arguments

Using assert()

You should know the details of implementation (e.g. assignment operator, subscripting operator, etc.)

Formal parameters, actual parameters

Constructors, Destructors

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Connecting Classes via Connecting Classes via CompositionComposition


Data members and Member Functions

You should know what happens to them when you connectclasses via Composition.


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Connecting Classes via Connecting Classes via InheritanceInheritance


See Lectures 15 & 16

Data members and Member Functions

You should know what happens to them when you connectclasses via Inheritance.


Multiple Inheritance

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STLSTL


See Lectures 20, 21 & 22

Containers: vector, list, map

Algorithms: find, sort, insert, erase

Iterators

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JavaJava


Program structure, JVM

Main function, creation & deletion of objects from the heap,how Java supports cross-platform application development?

Inheritance in Java

Paramater passing

how to pass objects?

Requirements when a class extends another class,What happens if you put a class inside another class?

See Java 1,2,3

See Java 2

See Java 3

Interface in Java

What happens when a class implements an interface?

See Java 3

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C++Static Members of Classes

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Static members of classes:If a member variable is declared static, there is only one instance of that in the program. A static variable is common to all class variables.

class P {public: static char c;static char c;};

char P::c = 'W';char P::c = 'W';int main() { P x,y; cout << x.cx.c; x.c x.c = 'A'; cout << y.cy.c;}

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1. When a copy of an object is required, such as in call-by-valuecall-by-value. SStr p;tr p; display(p);display(p);

2. When returningreturning an object by value from a function.

Point findMiddlePt ( Point p1,Point p2){Point findMiddlePt ( Point p1,Point p2){ Point temp ;Point temp ; //---do something

return temp;return temp;}}

3. When initializinginitializing an object to be a copy of another object of the same class.

Str x;Str x;//...other statements here

Str y(x);Str y(x); //y declared and initialized with xor

Str y = x;Str y = x; //y declared and initialized with x

When is a copy constructor called?SUMMARY

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Friend Functions/Classes

Friend functions

A 'friend'friend' function has access to access to all 'private' members all 'private' members of the class for which it is a 'friend'.

To declare a 'friend' function, include its prototypeprototype within the class, preceding it with the C++ keyword 'friend'.

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Friend Functions/Classes

class TT { public: friend void a();friend void a(); int int mm();(); private: // ...};

void a() {// can access // private data in T...}

class SS { public: friend int friend int TT::m();::m(); //...};

class X {public: friend class friend class TT;; //...};

Global function a()a() can access private data in class TT

m()m() can access private data in class SS

all functions of class TT can access private data in class XX

friendfriendss should be used with caution: they by-pass C++’s data hiding principle.

It is the responsibility of the code for which access is to be given to say who it’s friends are - i.e. who does it trust!

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Defining Operator OverloadingDefining Operator Overloading

To define an additional task to an operator, we must specify what itmeans in relation to the class to which the operator will be applied.

This is done with the help of a special function called operator function which describes the task.

General form of an operator function:

return typereturn type classname :: operator (op-arglist){ function body //task defined}

Operator being overloaded

operator is the function name

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PolymorphismPolymorphism

class two_dtwo_d {public: two_d(double a, double b) : x(a), y(b) {} virtualvirtual double areaarea(void) {return 0;return 0;}

protected: double x,y;};

area area is a called a virtualvirtual function.

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class rectrect : public two_dtwo_d{public: rect(double a, double b, double ht, double wd) : two_d(a,b), h(ht), w(wd) {} virtualvirtual double areaarea(void) {return w * h;return w * h;}

private: double h,w;};

area area is a called a virtualvirtual function.

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area() is a called a virtualvirtual function.

The run-time system knows the types of objects that pointers point to!

The appropriate The appropriate function is called when function is called when we ask forwe ask for p[i]->area()p[i]->area()

for (int i=0;i<4;i++) { total += p[i]->area()p[i]->area();

}

Here’s the code segment again:

circle c,d; rect e,f; two_d* p[4]; p[0]=&c; p[1]=&d; p[2]=&e; p[3]=&f;

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PurePure Virtual Function Virtual Function

class two_d {public: two_d(double a, double b) : x(a), y(b) {} virtual double area(void) virtual double area(void) = 0= 0;;protected: double x,y;};

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TemplatesTemplatesExample: VectorExample: Vector

Data members & some extra methods:Data members & some extra methods:

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template <class T>Vector<T>::Vector(int n=100) : size(n) { assert(n>0); p = new T[size]; assert(p != NULL);}

Constructor:Constructor:

protected: T* data; unsigned size;

void copy(const Vector<T>&);

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TemplatesTemplates

operator[ ]operator[ ]

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template <class T>T& Vector<T>::operator[](int i) { assert((i>=0) && (i<size)); return p[i];}

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TemplatesTemplates

operator =operator =

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template <class T> Vector<T>& operator=(const Vector<T>& v) { if(size > 0) { cout << "deleting previous contents..." << endl; delete [] data; } size = v.size; data = new T[size];

copy(v); return *this; }

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TemplatesTemplates

Copy constructorCopy constructor

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//Copy constructor: X-X-refVector(const Vector<T>& v) : size(v.size) { cout << "\ncopy constructor called." << endl;

data = new T[size]; copy(v);}

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TemplatesTemplates 1919

template<class T>void Vector<T> ::copy(const Vector<T>& v) {

// int minSize = (size < v.size)? size : v.size;// for(int i=0; i < minSize; i++) {

for(int i=0; i < size; i++) {data[i] = v.data[i];

}

}

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TemplatesTemplatesUsing a Template ClassUsing a Template Class

Finally, this is how we use a template class:Finally, this is how we use a template class:

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int main() { Vector<int> m(100); m[3] = 34;...}

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#include <iostream>#include <vector>using namespace std;

int main(){ vector<int> v; vector<int>::iterator it, start, end; for(int i=0;i<10;i++){ v.push_back(i); } cout << "v size = " << v.size() << endl; start = v.begin(); start += 3; // now points at element [3] end = start; end += 4; // now points at element [7] v.erase(start, end ); // erases 3,4,5,6 cout << "v size = " << v.size() << endl; for(it=v.begin();it<v.end();it++){ *it *= 10; } cout << "v contains: "; for(int i=0;i<v.size(); i++){ cout << " " << v[i]; } cout << endl;

}

Output:

% a.out

v size = 10

v size = 6

v contains: 0 10 20 70 80 90

vector<int> v;vector<int> v;A variable-sized vectorA variable-sized vector

the range includes all the elements between start and end, including the element pointed by start but but notnot the one the one pointed by end.pointed by end.

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map<string,int> m1, m2; map<string,int>::iterator iter; // points to a pair<string,int>

string one("One"); string two("Two"); string three("Three"); string four("Four"); string five("Five");

m1[one] = 1; m2[two] = 2; m1[three] = 3; m2[four] = 4; m1[five] = 5;

for(iter=m1.begin();iter!=m1.end();iter++){ cout << "Found " << iter->second << " keyed by " << iter->first << endl; } cout << endl;

m1.swap(m2);

for(iter=m1.begin();iter!=m1.end();iter++){ cout << "Found " << iter->second << " keyed by " << iter->first << endl; }

Note: map’s iterator is a pointer to a pair - dereferenced using members first and second

Output:

% a.out

Found 5 keyed by FiveFound 1 keyed by OneFound 3 keyed by Three

Found 4 keyed by FourFound 2 keyed by Two

map<key, val>map<key, val>An associative array (or dictionary, or table)An associative array (or dictionary, or table)

• acts like an array whose index can be any type that implements the < operator.• e.g. key=StudentID, val = Student’s data Record

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struct Entry { string name; int number; friend int operator<(const Entry& e1, const Entry& e2);};

int operator<(const Entry& e1, const Entry& e2) {return (e1.name < e2.name);

}

vector<Entry> v;...sort(v.begin(), v.end());

STL: vectorSTL: vector

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A map STL contains a built-in find function.

it = phoneBook.findfind("ZNapoleon");

if(it != phoneBook.end()) {cout << "Entry found." << endl;cout << it->first << ", " << it->second << endl;

} else {cout << "Entry is missing." << endl;

}

mapmap<string, int> phoneBook;//...

STL: mapSTL: map

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1 159.234LECTURE 159.234 LECTURE Review for Finals 2009 x OOP