ECE 462
Object-Oriented Programming
using C++ and Java
Lecture 1
Yung-Hsiang Lu
yunglu@purdue.edu
Textbook
• "Programming with Objects" by Kak, John-Wiley
• source code from the book and errata:
http://programming-with-objects.com/
• many executable examples about the
concepts explained in the book
• contains topics that are rarely
discussed in other books, such as
multiple inheritance
• provides frequent comparison
between C++ and Java
week 1 2
Experiment:
Directed Problem Solving in Labs
• This semester, we are conducting a pedagogical experiment, similar
to DPS in ECE270 and 362.
• All lectures are recorded and available on-line.
• Every week = 2 lectures + 1 lab
• There is no reduction of the course material because QA is
handled outside lectures and no time is wasted setting up computer
or demonstration of tools.
• Lab sessions = office hours. Twelve (12) lab assignments are
graded. Additional office hours are also available.
• You can watch the lecture videos at any time. You are encouraged
to watch the videos with classmates, pause, and discuss.
week 1 3
Advantages of DPS
• Determine your own pace. You can watch is once or
multiple times (asynchronous learning)
• Encourage group study by watch the video together.
• Promote self assessment, using the time you need.
• Provide more flexibility in utilizing your time.
• Enhance student-instructor interaction in labs
• Accommodate the wide range of students’ background
• Offer one-to-one attention to individual’s learning needs
during the lab hours
week 1 4
Disadvantage of DPS
• no classroom interaction with classmates ⇒ watch
lecture videos with classmates
• no classroom interaction with instructor ⇒ use lab hours
• cannot ask questions during lectures ⇒ post questions
in webct
• Please provide frequent feedback and suggestions
through webct discussion.
• Demonstration of webct video and discussion.
week 1 5
Grading
• 1% course evaluation (send email to instructor after completion)
• 1% “technology and education” survey and discussion, organized by
Professor Brown (in class, November)
• 4% homework = 0.5% x 8, in webct
• 12% lab assignments = 1% x 12
• 20% programming assignments = 4% x 5
• 10% exam 1 (in class, September 21, open book, no collaboration)
• 14% exam 2 (in class, October 19, open book, no collaboration)
• 18% exam 3 (in class, November 16, open book, no collaboration)
• 20% final exam (TBD, open book, no collaboration)
• > 85% A. 75% -85% B. 65% - 75% C ... after normalization by the
highest score (if < 100%) in class
• Each outcome is tested twice. Failing one or multiple outcomes in
both tests ⇒ F
week 1 6
Bonus Points
• Each person can receive up to 5 bonus points:
– up to 4 points, provide 5 or more questions for each
exam (posted in webct), one point per exam
– up to 5 points, scribe the lectures (every word) and
post it in webct, one point per lecture
– 1 point: the two people that have the most postings in
webct discussion before final exam
• No other bonus point will be given.
week 1 7
Lab Assignments
• Each person must submit 12 lab assignments. Only one
submission can be accept per session.
• Each assignment asks you to learn one programming
tool and must be signed off by the teaching assistant.
• You are welcome to use the lab hours even after you
have submitted all assignments.
• The instructor and the teaching assistant will be
available in the lab sessions as office hours. Additional
office hours can be arranged by appointment.
• You can discuss lab assignments with anyone.
week 1 8
Programming Assignments
• 3 regular programming assignments: 2 in Java and 1 in C++, each
4% of the grade.
• 1 programming assignment either Java or C++, divided into 2
stages: planning and implementation, each 4%.
• You can do each assignment alone or work with one classmate. You
may change the group mate for each assignment.
• You can discuss programming assignments with anyone but you are
allowed to share code only with your group mate. In this course,
all deadlines are firm (no extension and no exception for any
reason, including but not limited to earthquake, tsunami, tornado,
invasion by outer space aliens, power failure, fire, flood).
• Each person has one 24-hour “free” late day. If you have a group
mate, you two can have 2 free late days, use 2 days once, or one
day twice.
week 1 9
Programming Assignment 4
• You (and your group mate) decide what to do. You can
choose Java or C++ or both.
• Requirements:
– object-oriented
– graphical user interfaces + networking
– UML diagrams of all classes, at least 5 use cases, at
least 5 sequence diagrams, at least 1 state diagram
– schedule + testing plan and results
• Submit a detailed plan on November 9.
• Submit the program + documentation on November 30.
week 1 10
Exams
(open book, open note, individual)
• multiple choice, short answer (code statement), short code (several
lines)
• Final exam may contain several questions of slightly longer (about
10-20 lines) of code
• “zero-tolerance” of dishonesty: violations will be reported to the
associate head of ECE, no exception. We will use similarity
checking in your assignments.
• You can discuss lecture, homework, lab, or programming
assignments with anyone. You can share code with only your
programming partner (if you have one).
• Regarding must be submitted by a written request (or email) within
one week. You are not allowed to ask or discuss with TA about
regrading.
week 1 11
Prerequisites
• ECE 264
• Know how to write and compile C programs in UNIX-
based (e.g. Linux or Solaris) machines, such as gcc,
gdb, and Makefile
• Understand the concept of pointers in C
• We will not emphasize syntax. Instead, we will spend
more time on how to design and implement non-trivial
programs.
week 1 12
Objects
• Object: a “concrete and tangible” entity that can be separated with
unique properties. Examples: you, your book, your car, my
computer, Tom, Amy’s computer, a window on your computer
desktop, your phone, Sam’s digital camera, Jennifer’s pager ...
• Object can be "abstract": a triangle, a database, a browser ...
• Each object is unique and can be identified using name, serial
number, relationship with another object ...
• Each object has a set of states, such as location, speed, size,
address, phone number, on/off ...
• Each object has unique behavior, such as ring (phone), accelerate
and move (car), resize (window), take picture (camera), send email
(computer), display caller (pager)
week 1 13
Objects’ Properties
• Each object has three important properties:
– unique identity
– states (also called attributes), noun
– behavior (action), verb
• Objects can interact, for example
– You (object) press (action) the pedal (object) of your car (object).
As a result, your car accelerate (action).
– When your phone (object) rings (action) and alerts (action) you
(object) of an incoming call (state), you answer (action) the call
(state).
– You submit (action) homework (object) and it is graded (action)
with a score (state).
week 1 14
What is Class?
• A class provides
– a type (similar to “struct”) to create objects
– an interface (methods) for objects to interact (“send
messages”), such as setLineStyle and getArea
– a set of attributes
– implementation of the interfaces
– a base for derived classes
• Review: objects- concrete entities, such as John, your
car, my book, the phone on this desk... class- a
representation of the commonality of objects, such as
Human, MotorVehicle, MobilePhone...
week 1 15
Self Test
• We have many self tests. Pause the video and resume
when you are ready.
• In the following list, mark C as class and O as object.
• your home • Building
• MSEE • Tom’s PDA
• LaptopComputer • Wallet
• his wallet • Water
• the bottle of water I drank • BottleWater
yesterday • Restaurant
• my favorite restaurant • FastFoodRestaurant
• the McDonald across the street
week 1 16
Self Test Answers
• your home (O) • Building (C)
• MSEE (O) • Tom’s PDA (O)
• LaptopComputer (C) • Wallet (C)
• his wallet (O) • Water (C)
• the bottle of water I drank • BottleWater (C)
yesterday (O) • Restaurant (C)
• my favorite restaurant (O) • FastFoodRestaurant (C), may
• the McDonald across the street be a derived class of
(O) Restaurant
week 1 17
Objects and Classes
• Organize objects with similar properties (states and
behavior) into classes: human, car, computer, phone,
window, circle, rectangle, triangle, bridge, skyscraper ...
• Inheritance: find commonality among classes (not
objects) and create a base class that represents the
common interfaces and behavior
• Common interface of Shape: Shape
– center
– line style and thickness
Circle Rectangle
– area ...
– But areas are computed differently Triangle
week 1 18
Inheritance
to achieve better code reuse
class Shape {
public void setColor(Color inColor);
public void setLineStyle(LineStyle lineStyle);
public void setLineThickness(int thickness);
}
class Circle extends Shape { /* Circle is a derived class of Shape */
}
Circle cobj = new Circle(); /* create an object */
cobj.setColor(Color.RED);
cobj.setLineStyle(LineStyle.Solid);
Coding Convention:
class name: capital letter, noun
action: starting with lower case, verb
week 1 19
Inheritance
reuse attributes from base class
class Shape {
private Color s_Color;
private LineStyle s_LineStyle;
private int s_thickness;
}
class Circle extends Shape {
}
Circle cobj = new Circle();
cobj.s_Color ⇐ the color attribute
Coding Convention: attribute: start with a lower case
letter of the class’ name, followed by an underscore
week 1 20
Polymorphism
Objects of Different Derived Classes Behave Differently
class Shape {
public float getArea();
}
class Circle extends Shape {
private float c_radius; // attribute unique to this derived class
public float getArea() { return (c_radius * c_radius * Math.PI); }
/* the formula to calculate area is unique for each derived class */
}
class Rectangle extends Shape {
private float r_width, r_height;
public float getArea() { return (r_width * r_height); }
}
week 1 21
ECE 462
Object-Oriented Programming
using C++ and Java
Lecture 2
Yung-Hsiang Lu
yunglu@purdue.edu
Polymorphism
Objects of Different Derived Classes Behave Differently
class Shape {
public float getArea();
}
class Circle extends Shape {
private float c_radius; // attribute unique to this derived class
public float getArea() { return (c_radius * c_radius * Math.PI); }
/* the formula to calculate area is unique for each derived class */
}
class Rectangle extends Shape {
private float r_width, r_height;
public float getArea() { return (r_width * r_height); }
}
week 1 23
Reuse or Not?
• Attribute:
– If an attribute is shared by all derived classes, the attribute
should be declared in the base class. example: color, line style,
thickness.
– If an attribute is unique to a class, it should be declared in this
derived class, example: radius for circle.
• Behavior (member function, method, message):
– If a method is available (interface) to all derived classes, such as
getArea and setLineStyle, it should be declared in the base
class.
– If the method’s implementation is applicable to all derived
classes, it should be implemented in the base class.
– If the implementation is unique to each derived class, it should
be implemented in the derived classes.
week 1 24
Base or Derived Classes
• base: more general, including only common attributes
and methods, “smaller” (do not call it superclass)
• derived: more specific, including additional attributes and
methods, “larger” (do not call it subclass).
• Any object of a derived class is also an object of the
base class, false in the other direction.
• Human (base): Student (derived) ⇒ a student object
includes additional attributes, such as student ID, school
name, number of courses taking ... and additional
methods, such as submitHomework ... A student object
is also a Human object.
week 1 25
More Examples about Base / Derived
• attributes:
– base, MotorVehicle: engine size (int) , brand (string)
– derived, Sedan: sunroof or not (boolean)
– derived Truck: towing capacity (int)
– derived MotorCycle ...
• methods:
– MotorVehicle: accelerate MotorVehicle
– Truck: load cargo
– ...
Sedan MotorCycle
Truck
week 1 26
Self Test
• In the following pairs, which one should be the base
class and which one should be the derived class?
• Computer / DesktopComputer • JetPlane / Airplane
• CollegeStudent / Student • Furniture / Chair
• Teacher / CollegeProfessor • Boat / SteamBoat
• DrinkingWater / Liquid • Electronics / Computer /
• Metal / Iron LaptopComputer
• Eagle / Bird
week 1 27
• Computer (B) / • JetPlane / Airplane (B)
DesktopComputer • Furniture (B) / Chair
• CollegeStudent / Student (B) • Boat (B) / SteamBoat
• Teacher (B) / CollegeProfessor • Electronics (B) / Computer
• DrinkingWater / Liquid (B) (D1) / LaptopComputer (D2)
• Metal (B) / Iron ⇒ 3 layers of class relationship
• Eagle / Bird (B)
• The relationship among base and derived classes is
called the class hierarchy.
• Class hierarchy is a programming concept, not
biological classification. Design a class hierarchy based
on the need of the program. For example, whether
“canFly” is a property of Bird and whether Chicken
should be a derived class of Bird.
week 1 28
Self Test
• In the following base / derived classes, mark which
method should be declared / implemented in base and
which should be declared / implemented in derived.
• Computer / Laptop: • Human / Student: askAge /
printDocument / chargeBattery askGender
• MotorVehicle / Truck: • Telephone / MobilePhone:
accelerate / decelerate dialNumber /
• Building / OfficeBuilding: computerRoamRate
turnOnHeater / shutOffWater • Construction / Bridge:
getSpanLength / getHeight
week 1 29
• Computer / Laptop: • Human / Student: askAge (B) /
printDocument (B) / askGender (B)
chargeBattery (D) • Telephone / MobilePhone:
• MotorVehicle / Truck: dialNumber (B) /
accelerate (B) / decelerate (B) computerRoamRate (D)
• Building / OfficeBuilding: • Construction / Bridge:
turnOnHeater (B) / getSpanLength (B) / getHeight
shutOffWater (B) (B)
• These examples illustrate that in many cases, the
methods can be declared in the base classes and
reused in the derived classes.
• As shown in the example of getArea, the implementation
may be unique in derived classes.
week 1 30
Encapsulation
Hiding Information Inside Objects
• Objects can interact through only public methods. Methods and
attributes can be declared as private or protected.
– private: accessible (read / write attributes, or call methods) by
only the class
– protected: accessible by the class or its derived classes
• Objects do not know other objects’ internal structures, for example,
how can a Shape object calculates its area.
• Encapsulation ensures that objects’ attributes cannot be accidentally
modified externally and allows future improvement without affecting
the interfaces.
• If an object wants another object to do something, the first object
sends a message to the second object.
week 1 31
Four Key Concepts about OOP
(beginning of Ch 3)
• class
• encapsulation
• inheritance
• polymorphism
week 1 32
Demonstration of Building
Graphical User Interface
Using Netbeans
in ECN Linux machine, netbeans is
available at /usr/opt/bin/netbeans
Lab 1: Java GUI using netbeans
• create a calculator that can handle +, -, *, and /.
• allow multiple digits
• use integer in Java
• do not worry about
– fractions
– overflow or underflow
– divided by zero
– set or reset memory
– backspace
– sign toggle
– square root
week 1 34
What is Method / Message
A message is a request to an object to do something. An object
can receive a message if it is declared as a method in a base class
or the corresponding class.
class MotorVehicle {
public void accelerate(int val);
}
class Truck extends MotorVehicle {
public void towTrailer(Trailer tra);
}
Truck t = new Truck();
t.accelerate(50); t.towTrailer(...);
week 1 35
Interactions Among Objects
• An OO (object-oriented) program, many objects are created and
they interact by “sending messages”, for example,
– A Driver object sends a message “accelerate” to a MotorVehicle
object.
– An Instructor object sends a message “submitHomework” to a
Student object.
– A Caller object sends a message “callNumber” to a MobilePhone
object.
class ClassName {
public void doSomething(...)
}
ClassName anobject;
anobject.doSomething(...); /* this object is asked to do something */
week 1 36
class Shape {
abstract public float getArea(); // interface, no implementation
}
class Circle extends Shape {
private float c_radius; // attribute unique to this derived class
public float getArea() { return (c_radius * c_radius * Math.PI); }
/* the formula to calculate area is unique for each derived class */
}
class Rectangle extends Shape {
private float r_width, r_height;
public float getArea() { return (r_width * r_height); }
}
An abstract method is declared as an interface and it must be
implemented in the derived classes.
week 1 37
Message
• not a network concept
• the mechanism to interact with an object
– ask a bridge about its length
– turn on a light (no parameter)
– accelerate a car (parameter?)
– add a customer to a database (parameter =
customer)
– ask a customer of the credit number
• disallowed messages are checked at compile time:
compiler error if you ask a light bulb to accelerate.
week 1 38
Self Test
Determine which object sends messages:
obj.message(arg) means a message is sent to object obj
with parameter arg.
• A Driver object (dobj) sends an “accelerate” message to
a Car object (cobj)
• A Teacher object (tobj) sends a message to a Student
object (sobj) to submit homework.
• A Computer object (cobj) sends a Packet object (pobj) to
a Network object (nobj).
week 1 39
• A Driver object (dobj) sends an “accelerate” message to
a Car object (cobj)
⇒ cobj.accelerate();
• A Teacher object (tobj) sends a message to a Student
object (sobj) to submit a Homework object (hobj).
⇒ sobj.submit(hobj);
• A Computer object (cobj) sends a Packet object (pobj) to
a Network object (nobj).
⇒ nobj.send(pobj);
The object is the recipient of the message. Where is the
sender? It is implicit by the location of the message.
week 1 40
class Driver { • The “sender” is the method
private Car d_car; where a message is sent.
public void driveCar(...) { • The recipient must be
d_car.accelerate(); initialized (not discussed yet)
before sending any message.
}
}
class Teacher {
private Student t_stu;
public void teachClass(...) {
t_stu.submit(hobj);
}
}
week 1 41
Object Type
• If an object is declared to be an instance of a class, the
object can refer to an object of a derived class.
• example
Human obj1;
Student obj2;
obj1 = obj2; // assign a student to obj1, ok
obj2 = obj1; // wrong, a human may not be a student
aobj = bobj ⇒ assign bobj to aobj, aobj (e.g. Human or Student) can
be bobj (e.g. Student), aobj is in the same class or more general
(base class).
week 1 42
class Shape {
abstract public float getArea(); // interface, no implementation
}
class Circle extends Shape {
private float c_radius; // attribute unique to this derived class
public float getArea() { return (c_radius * c_radius * Math.PI); }
}
class Rectangle extends Shape {
private float r_width, r_height;
public float getArea() { return (r_width * r_height); }
}
Rectangle robj = new Shape;
Shape sobj = new Rectangle; // WRONG
sobj.getArea() ⇒ call Rectange’s getAreaCircle cobj = new Rectangle;
sobj = new Circle; // WRONG
sobj.getArea() ⇒ call Circle’s getArea
week 1 43
Object Creation
• Programmer-provided “constructor”: a method with the same name
as the class. The method may take input arguments.
• Constructors can create objects in consistent ways and no attributes
are left uninitialized.
• In C++ and Java, a function can have different numbers and types of
input parameters (called overloading).
constructor
class Student { class Student {
public Student() { public Student(String school) {
... ...
} }
} }
week 1 44
// ----------------------- User.java
class User {
private String name;
private int age;
public User( String str, int yy ) { name = str; age = yy; }
public void print() {
System.out.println( "name: " + name + " age: " + age );
}
similar to (int argc, char * argv[]) but
} Java arrays know their lengths
class Test {
public static void main( String[] args ) {
User u = new User("Zaphod", 23 );
u.print();
}
}
week 1 45
