Embed Size (px)
Citation preview
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie
COMP 14Introduction to Programming
Adrian Ilie
July 8, 2005
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie2
COMP 14 So Far...
• Problem Solving• Mathematical Calculations• Output• User Input• File I/O• Selection (if, if-else, switch)• Loops (while, do...while, for)
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie3
COMP 14 Next...
• Object-Oriented Design• Writing Methods♦ pieces of code that we give a name
• Writing Classes♦ organize related pieces of information
• Arrays♦ access multiple pieces of information
with a single identifier
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie4
Object-Oriented Design
• What is it?
Designing a solution to a problem by first identifying components called objects, and determining how the objects interact with each other
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie5
ObjectsVCR Example
• Use it without knowing how it's made
• Internal parts are hidden -- only interact with the provided buttons
• Can't modify the functions of a VCR -- record button always records, play button always plays
Same is true for objects (like Strings) that are provided by Java
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie6
Objects
Consist of data and operations on the data• Data - descriptive characteristics• Operations - what it can do (or what can be
done to it)
Example A coin that can be flipped so that its face
shows either "heads" or "tails"♦ data: its current face (heads or tails)♦ operations: it can be flipped
Operations can change data.
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie7
ObjectsAnd Methods and Classes
• We represent operations with methods♦ group of statements that are given a name
• We can use objects and their methods without knowing exactly how the methods work
• An object is an instance of a class. A class is the blueprint of an object.♦ the class provides the methods that can operate
on an object of that class
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie8
Classes
• A class contains data declarations and method declarations
• A class is a description of an object♦ just a model, not an actual object♦ you can think of the concept of a book without
thinking of a particular book
• A class is no more an object than a blueprint is an actual house
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie9
Object-Oriented DesignSimplified Methodology
1. Write down detailed description of problem
2. Identify all (relevant) nouns and verbs
3. From list of nouns, select objects
4. Identify data components of each object
5. From list of verbs, select operations
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie10
Object-Oriented Design Example 1
• Problem Statement♦ Write a program to input the length and
width of a rectangle and calculate and print the perimeter and area of the rectangle
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie11
Example 1Building a Rectangle
• Identify nouns♦ length, width, rectangle, perimeter,
area
• Identify each class♦ length of a rectangle♦ width of a rectangle♦ perimeter of a rectangle♦ area of a rectangle
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie12
Example 1Building a Rectangle
• Identify data members for each class♦ nouns: length, width,
area, perimeter♦ what are the essential
nouns for describing the rectangle?
♦ area and perimeter can be computed if we know the length and width
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie13
Example 1Building a Rectangle
• Identify operations for each class♦ input, calculate, print♦ setLength♦ setWidth♦ computePerimeter♦ computeArea♦ print♦ getLength♦ getWidth
directly from problemstatement
customary to include operations to get the value of the data members
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie14
class Rectangle Data Members and Operations
Last Step:design and implement an algorithm for each operation
class name
data members
operations(methods)
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie15
Anatomy of a Class
• A class contains data declarations and method declarations
int width;int length;
Data declarations
Method declarations(operations)
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie16
Classes and Objects
Rectangle
A class(the concept)
length = 15, width = 3
An object(the realization)
length = 20, width = 6
length = 15, width = 15
Multiple objectsfrom the same class
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie17
Object-Oriented Design Example 2
A place to buy candy is from a candy machine. A new candy machine is bought for the gym, but it is not working properly. The candy machine has four dispensers to hold and release items sold by the candy machine and a cash register. The machine sells four products —candies, chips, gum, and cookies—each stored in a separate dispenser. You have been asked to write a program for this candy machine so that it can be put into operation.
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie18
Object-Oriented Design: Example 2
The program should do the following:• Show the customer the different
products sold by the candy machine.• Let the customer make the selection.• Show the customer the cost of the item
selected.• Accept money from the customer.• Return change.• Release the item, that is, make the
sale.
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie19
Object-Oriented Design: Example 2
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie20
Object-Oriented Design: Example 2
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie21
Non-Concrete Objects
• Objects in programs don't always have real-world analogs
Exampleobject: error messagedata: text of the error messageoperation: print the text of the error message to the screen
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Adrian Ilie22
Next in Comp14
• Tomorrow: writing methods
• Monday: review for mid-term♦ Bring laptops♦ Write questions before coming to class
