CSC 200 Study Guide – Fall 2010
Chapter 16 Object-Oriented Programming
Chapter Learning Objectives
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To use object-oriented programming to make programs
easier to develop in teams, more robust, and easier to
debug.
To understand such features of object-oriented programs
as polymorphism, encapsulation, inheritance and
aggregation.
To be able to choose between different styles of
programming for different purposes.
Study Smart, Not Hard
Learn the information as we go through the semester. Spend a hour or so a day a
week before the exam to study. It is impossible to cram all this information into
your brain if you wait until night before the exam. Read all the short programs in
this chapter to make sure that you understand exactly what they do. You should
understand them much easier now than you did earlier this semester.
16.1 History of Objects
See Chapter 15 Study Guide for more details on the history of programming
languages.
Object-Oriented Programming Model (OOPs) is the newest language paradigm.
This model views the world as a collection of interacting objects. Each object is
defined by a class, and the actions are defined by methods. These languages allow the
programmer to express algorithms using a hierarchy of objects.
Alan Kay invented the term object-oriented programming and created the first objectoriented language called SmallTalk. Alan earned the 2003 Turing Award for his
pioneering world in OOPs. (Note: Book has wrong date) One of his mentors (during
graduate school) was Ivan Sutherland, who had done pioneering graphics
programs including Sketchpad. “Software is actually a simulation of world. By
making software model the world, it becomes clearer how to make software.”
Adele Goldberg also worked on the SmallTalk project and was a co-author of the
first book about SmallTalk.
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Chapter 16 Study Guide
Benefits of Object-Oriented Programming
1. Manage complexity - each object is self-contained so it is much easier to
debug errors and manage the project.
2. Supports robustness - Robustness is the ability of a computer system to
cope with errors during execution or the ability of an algorithm to continue
to operate despite abnormalities in input or calculations.
3. Supports reuse - This means you can reuse objects (and code) more easily
than traditional programming methods. Inheritance in OOPs naturally
creates reusability.
16.2 Working with Turtles
(Page 361) Dr. Seymour Papert, at MIT, created a system called Logo that
programmed turtles on a screen to help young children think and solve problems
in the late 1960s.
(Not in book) Karel the Robot was another popular Logo type language created
and used at Stanford University by Richard E. Pattis in 1981. This language used
a robot called Karel instead of turtles. This program was taught in Computer
Science classes at NRCC and RU in the 1990s. See the Karel the Robot link for
example code. It looks very similar to JES.
In this section, you learn how to use the Turtle objects available in JES.
1. To start a turtle program in JES, you must create the world, and create an
instance of the world.
2. Next you create and name an instance of a turtle.
3. Now you can send messages to the turtle and make it move on the screen
and draw.
See the Built-in JES for Turtle Objects (later in this study guide) for details on
creating worlds, turtle and methods.
16.3 Teaching Turtles New Tricks
In this section, you learn how to create a subclass of a turtle and teach it new
tricks.
See Programs 146 and 147 on pages 369 – 370 for details on creating a subclass
called smartTurtle from the built-in turtle class/object.
16.4 An Object-Oriented Slide Show
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Chapter 16 Study Guide
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Skip this entire section (pages 371 – 380) except for the definition of
encapsulation (on page 373) and polymorphism (on page 376).
16.4.3 Why Objects?
In this section, more benefits of OOPs are described. Object-oriented
programming is great for GUI applications, interactive games and interactive
applications. Some benefits are listed in Section 16.1 (earlier in this study
guide). Other benefits are PIE, polymorphism, inheritance, and
encapsulation.
Built-in JES for Turtle Objects
 makeWorld()
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(page 362) creates a new world instance for turtles to explore.
makeTurtle(worldName)
(page 363) creates a new turtle instance that appears in the center of the
world
.forward() or .forward(pixels)
(page 363) method that moves the turtle forward 100 pixels (default) or
the number of pixels specified
.turnLeft() or turnRight()
(page 364) method that turns the turtle left or right
.turn(degrees)
(page 364) method that turns the turtle the specified number of degrees.
Remember 360 degrees is a full spin.
.penUp() or .penDown()
(page 366) method that for the turtle to pick up or put down a drawing pen
.moveTo(x,y)
(page 367) method that moves a turtle to the specified coordinate position
.setPenWidth(width)
(page 367) method that sets the turtle pen to the specified width
.setColor(color)
(page 367) method that changes the turtle pen to the specified color
Key Terms
Make sure that you understand the definition of the following terms. The page is given
from the textbook. Each term is either bold or italic in the textbook. Use your textbook
and other sources such as webopedia.com , Wikipedia.org or your favorite search engine
to add the definitions to the list.
Remember OOP is easy as PIE. A language must suuport Polymorphism, Inheritance and
Encapsulation to be classified as a OOP language.
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Chapter 16 Study Guide
Page
Term
Definition
360
Object-oriented
programming
See previous page of this study guide.
361
object
The primary items in an object oriented program.
These are the nouns in the system you are
modeling.
class
The formal definition of an object. Similar to the
function definitions we have been using all semester.
361
An instance is an occurrence or an object in a
Instance
361
program. Analogy: The class is the recipe for
an object such as a cake and the baked cake
would be the instance.
Method
Methods are the verbs in an OOP project. The
methods are associated with a particular object. For
example if the object was rabbit, then methods
could be hop, dig(hole), eat(carrots), wiggle(nose).
Polymorphism
Polymorphism means that you can have methods
with the exact same name that will do the correct
process for different objects or even in the same
object. See Program 147 smartTurtle (page 147) for
an example. We have 2 methods named
drawSquare but it executes the correct method
based on the number of inputs.
Inheritance
Inheritance is a powerful feature where an object
can inherit all the methods and properties of a
parent object. See Program 146 smartTurtle (page
369) for an example. All the methods that a turtle
object can do such as moveTo, forward, turnRight
etc. are available to the smartTurtle because it is a
subclass(child) of the turtle object built into JES.
Encapsulation
Encapsulation means that the object properties and
methods are all defined in a single class (section of
code). This makes it much easier to debug and
program. See Program 147 smartTurtle (page 147)
for an example. All the methods for the smartTurtle
are contained within the class code.
376
381
373
Jython / JES Programming Summary
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Ignore the Programming Summary in the book as these are the graphic
commands from the slide show section that we skipped.
Last Update: July 13, 2017
Study Guide created by Carlotta Eaton
For Introduction to Computing and Programming in Python – A Multimedia Approach by Guzdial & Ericson 2nd
edition
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Chapter 16 Study Guide
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