An Object-Oriented Approach to Programming Logic and Design Second Edition Chapter 1 An Overview of...

An Object-Oriented Approach to Programming Logic and Design

Second Edition

Chapter 1

An Overview of Computers and Logic

An Object-Oriented Approach to Programming Logic and Design 2

Objectives

• Learn about computer components and operations

• Learn about the evolution of programming techniques

• Learn about the steps involved in the programming process

• Learn about flowcharts and pseudocode statements


Objectives (cont’d.)

• Create an application class with a main()method

• Use and name variables

• Assign values to variables

• Describe data types

• Learn about various forms of input


Understanding Computer Components and Operations

• Two major computer system components– Hardware

• Equipment or devices associated with the computer

– Software• Programs (sets of instructions) written by programmers

• Application software: applied to a task (word processing, spreadsheets, payroll, etc.)

• System software: manages computer resources


Understanding Computer Components and Operations (cont’d.)

• Four major hardware and software operations– Input– Processing– Output– Storage

• Input operation– A means for data to enter computer through an input

device• Mouse

• Keyboard



• Processing data operation– Organizing – Checking for accuracy– Performing mathematical operations– Tasks occur in central processing unit (CPU)

• Using machine instructions

– Software • Provides machine instructions to CPU

• Written using programming languages



• Output operation– A means to view, print, interpret, store data using

output devices• Printer

• Monitor

– Hardcopy• Printed computer output

– Softcopy• Screen output



• Storage operation– Storing output information on storage device

hardware• Magnetic disks, compact discs, USB drives

• Computer software– Instructions controlling data manipulation

• Data input

• Data processing

• Data output or storage form

– Gives hardware a purpose



• Obtaining programmer’s instructions (software)– Buying prewritten software stored on – Downloading software from the web– Write your own software instructions

• Enter instructions through hardware devices

• Store on storage device (disk, CD)



• Programming languages– Common languages

• Visual Basic, C#, C++, COBOL, RPG, Fortran, JAVA

– Programmers may specialize

• Syntax– Rules governing usage and punctuation– Must be perfect



• Machine language– Circuitry consisting of millions of on-off switches– Computer’s on-off circuitry language

• Compilers and interpreters – Language translation software– Identify correct/incorrect language use

• Compilers – Create and store reusable machine instructions

• Interpreters – Interpret programming language at run-time



• Two programming language errors– Syntax errors

• Incorrect spelling

• Incorrect structure of language elements

– Semantic (logic) errors• Incorrect instructions

• Incorrect order of instructions

• Logic– Providing computer instructions in a specific

sequence



• Logic (cont’d.)– Example: a logic error in cake-making instructions

• Stir

• Add two eggs

• Add a gallon of gasoline

• Bake at 350 degrees for 45 minutes

• Add three cups of flour

• Run or executed – Occurs after program written and compiled

successfully



• Program instructions example– Written in English-like language– Three operations (input, processing, output)

Get inputNumber.

Compute calculatedAnswer as inputNumber times 2.

Print calculatedAnswer.


Understanding the Evolutionof Programming Techniques

• Storage categories– Internal and external needed by computer system– Internal storage

• Memory, main memory, primary memory

• Volatile main memory: lost when power turned off

• Inside machine

• Most often discussed in book


Understanding the Evolutionof Programming Techniques (cont’d.)

• Storage categories (cont’d.)– External storage

• Persistent (relatively permanent) storage

• Outside main memory (not necessarily outside computer)

• Exists in devices– Disk drives: hard and floppy– Flash media– Magnetic tape



• Program execution– Program copy stored in main memory– Required data must be in memory location

• Program calls location to obtain data

• Processing occurs

• Output displayed



• Modern computer programs– Around since 1940s

• Oldest programming languages– Programmers worked with memory addresses– Memorized awkward codes associated with machine

languages– Written as one piece


Understanding the Evolution of Programming Techniques (cont’d.)

• Newer programming languages– Look like natural language– Easier to use– Reasons for ease of use

• Use meaningful names for memory locations

• No awkward memory addresses

• Allow creation of self-contained modules or program segments

• Can be pieced together



• Program development techniques– Procedural programming

• Procedures created to manipulate data

• Actions carried out (getting input data for an employee and writing the calculations)

• Breaks process into manageable subtasks



• Program development techniques (cont’d.)– Object-Oriented programming (OOP)

• Objects, attributes, behaviors, states

• Attributes: object feature

• Behaviors: what object does

• States: set of all values of attributes

• Describes objects’ features or attributes



• Program development techniques (cont’d.)– Differences

• Programmer focus area in early stage

• Object-oriented approach application types– Computer simulations

• Create a model

– Graphical user interfaces• Users interact with program in graphical environment

• Natural use for object orientation


Understanding the Programming Process

• Computer software system development

• Three object-oriented approach tasks– Object-oriented analysis (OOA)

• Analyzing the system

– Object-oriented design (OOD)• Designing the system

– Object-oriented programming (OOP)• Writing the programs


1. Understanding the Problem

• Programmer– Write programs to satisfy others needs– Provide services to users

• First understand what users want

• Well designed program– Steps might involve a short meeting

• Poorly designed program– Steps might take many meeting hours

• Thoroughly understanding problem– A most difficult aspect of programming


2. Envisioning the Objects

• Programmer – Envisions objects needed– Writes programming language instructions to create

objects• Distinct steps

– Data modeling• Identify all manipulated objects and relations

– Create class• General object category

– Establish communication means• Between objects, user


3. Planning the Logic

• Heart of programming process

• Programmer– Plans program steps – Decides steps to include and order

• Leads from available input to desired output

– Plans the solution: two tools• Flowcharts and pseudocode

• Both use English-like code

– Language syntax not a concern


3. Planning the Logic (cont’d.)

• Think about all possible data values program might encounter– How to handle each scenario

• Desk-checking– Walking through program’s logic on paper

• Before writing the program

• Focus of course


4. Coding the Program

• Write class definitions– Descriptions data in each class– Operations performed with data in each class

• Object-oriented languages– C++, C#, Java, Visual Basic, Smalltalk, OO COBOL,

Simula– Similarity

• All create objects and establishing communication


4. Coding the Program (cont’d.)

• Program object and logic needed to work with the objects – Executed using any number of languages

• Syntax (correct spelling and punctuation )– Concern once language chosen

• Experienced programmers– Combine planning and program coding in one step


5. Translating the Program Code

• Many programming languages• Computer knows one language

– Its machine language consisting of many 1s and 0s• Translator programs (compilers or interpreters)

– Change English-like high-level programming into low-level machine language

• Executable program

• Syntax error – Issues when translator cannot translate the code– Must be corrected to allow compilation to complete


5. Translating the Program Code (cont’d.)

Figure 1-1 Creating an executable program.


6. Testing the Program

• Syntax error free program – Not necessarily free of logical errors– Must test for logical errors

• Requires entering of sample data– Select test data carefully– Error discovery may require changes

• To program logic

• To actual object design

• Process resembles syntax error correction cycle


7. Putting the Program into Production

• Program adequately tested – Ready for organizational use

• Putting program into production– Time to implement

• Can be short or long

• Depends on program nature, size and user needs

– Factors• Training, data format changes, new platform causing

users to make choices in unanticipated combinations


7. Putting the Program into Production (cont’d.)

• Non working program may cause significant monetary loss

• Testing before deployment must be thorough

• Conversion– Entire set of actions organization takes to switch over

to new program (set of programs)• May take months or years to accomplish


8. Maintaining the Program

• Maintenance– Process of making required changes

• Reasons – New legislated tax rates– Input file format alterations– End user requires additional information

• Not included in original output specifications


9. Retiring the Program

• Final programming process step

• Program no longer needed by organization

• New program in process of going into production


Using Flowcharts andPseudocode Statements

• Flowchart– Pictorial representation of logical program steps – Program steps in boxes

• Connected with flowlines (arrows)• Shows processing order

• Pseudocode– English-like representation of logical program steps– Looks like programming language (is not)

• Important part of permanent documentation– Design and operation of software system


Using Flowcharts andPseudocode Statements (cont’d.)

Figure 1-2 Flowchart of number-doubling problem


Creating an Application Class with a main() Method

• Purely object-oriented programming languages – Every statement (application) part of class – “Pure View”

• Application– Program accomplishing some task

• Application pseudocode– Begins with word class – Ends with word endClass

• No object-oriented programming language uses endClass

• Used here for clarity


Creating an Application Class with a main() Method (cont’d.)

• Method– Set of statements performing task or group of tasks– Where program actions take place

• If class contains one executable method – Method named main()

• Identifier– Name of programming object

• Class, method, or variable



Figure 1-3 Flowchart and pseudocode for main() method that prints “Hello”



• Specific programming languages – Have rules for identifier structure

• Book pseudocode rules– Identifier names

• One word• Letters, digits, hyphens, underscores• No spaces

– Identifiers should have appropriate meaning– Compound words allowed

• Example: Helloclass



• main() statement– Method header

• Class containing main() method– An executable program

• Every method ends with return statement• main() method action statements

– Placed between main() method header and return statement



Figure 1-4 The Hello class written in the Java programming language

Figure 1-5 The Hello class written in the C# programming language


Using and Naming Variables

• Variables (fields)– Memory locations – Contents can change over time– Holds just one value at any given time

• Most objects in programs contain variables holding objects’ attributes

• Same rules for naming variables as naming classes


Using and Naming Variables (cont’d.)

Table 1-1 Valid and invalid variable names for an employee’s last name


Assigning Values to Variables

• Assignment statement– Statement assigning values to variables– Example: calculatedAnswer = inputNumber * 2

• Assignment operator– Example: equal sign– Requires memory location name on left side where

result stored

• Named constant– Named memory location (similar to variable)

• Value never changes during program execution


Assigning Values to Variables (cont’d.)

• High-level computer language– Programmers pick reasonable “English” name for

memory address• Computer keeps track of memory location

– Mathematical operations• Performed on memory address contents

– Operator precedence rules• Multiplication and division: precedence over addition

and subtraction

• Assignment operator has very low precedence


Understanding Data Types

• Basic data types: text and numeric

• Numeric constant (43)– Specific numeric value– Does not change– Digits with no quotation marks– Used for numeric calculations

• String constant (“chris”)– Specific character set enclosed in double quotes

• Character constant: single quotes (‘C’)


Understanding Data Types (cont’d.)

• Two distinct variable types– Numeric variable

• Holds a number

– Character variables• Hold single character

• String variables hold group of characters

– Distinguish between numeric and character• Computers handle two data types differently

– Language syntax rules define data type to expect• Done differently in every language



• Variable declaration statement– Contains data type and identifier

• Initializing a variable– Setting initial starting variable value– Popular languages (C++, C#, java, Visual Basic)

• Distinguish integer (whole number) numeric variables and floating-point (fractional) numeric variables containing decimal point

• Three broad types of variables– Numeric, character, string



• Garbage value– Uninitialized variable containing unknown value

• Default value– Automatic values for uninitialized variables

• Text or character data handled differently from numeric data (every computer)

• First step in writing programs– Identifying variables correctly

• Numeric, character, string

– Any programming language



Table 1-2 Some examples of legal and illegal assignments


Figure 1-6 Flowchart and pseudocode for the DoubleNumber class


Understanding VariousForms of Input

• Simple programs require simple data– Data values often entered from keyboard

• Users presented with a prompt

• Message on monitor asking for user response

– User interface • User’s means of interacting with the computer

– Command prompt• Input area on computer screen

• User can type text that communicates with computer’s operating system


Understanding VariousForms of Input (cont’d.)

Figure 1-7 A prompt followed by a response and output in a command-line environment



Figure 1-8 Flowchart and pseudocode for prompt and response in number-doubling program



• Text environment– Many programs do not run at command prompt – Run using GUI

• Typically contains graphical controls (buttons and text boxes)

• User can manipulate with a mouse or other pointing device



Figure 1-9 A prompt, a response, and output in a GUI environment



Figure 1-10 Flowchart and pseudocode for text box response in number-doubling program


Summary

• Hardware and software accomplish four major operations: input, processing, output, and storage

• Computer programming languages used to write machine instructions– Requires specific syntax

• Procedural programming focuses on procedures programmers creates to manipulate data

• OOP focuses on objects– Describes features or attributes and their behaviors


Summary (cont’d.)

• Programmer – Identifies objects and classes, codes program,

translates into machine language, tests, puts into production

• Flowcharts and/or pseudocode used to plan programming solution logic

• Program actions occur within a method

• Variables – Named memory locations, contents can vary– Choose meaningful variable names


Summary (cont’d.)

• Assignment always takes place from right to left

• Variable declaration tells computer type of data to expect

• Numeric, character, and string variables handled differently by computer

• User input data – Text or graphical environment– File stored alone or in database

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