COMP 14 Introduction to Programming Miguel A Otaduy May 24 2004 COMP 14 So Far Problem Solving Mathematical Calculations Output User Input File I O Selection if if else switch Loops while do while for 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 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 Objects VCR 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 Objects Consists 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 Objects And 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 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 Object Oriented Design Simplified 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 operation 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 Example 1 Building 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 Example 1 Building 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 Example 1 Building a Rectangle Identify operations for each class input calculate print setLength setWidth directly from problem computePerimeter statement computeArea print customary to include getLength operations to get the value of getWidth the data members class Rectangle Data Members and Operations class name data members operations methods Last Step design and implement an algorithm for each operation Anatomy of a Class A class contains data declarations and method declarations int width int length Data declarations Method declarations operations Classes and Objects A class the concept Rectangl e Multiple objects from the same class An object the realization length 15 width 3 length 20 width 6 length 15 width 15 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 multiple objects classes pgs 302 305 Non Concrete Objects Objects in programs don t always have realworld analogs Example object error message data text of the error message operation print the text of the error message to the screen Next in Comp14 Tomorrow writing methods Wednesday review for mid term Bring laptops Write questions before coming to class
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