1

Problem SolvingProblem Solving

The purpose of writing a program is to solve a problemThe purpose of writing a program is to solve a problem

The general steps in problem solving are:The general steps in problem solving are:

• Understand the problemUnderstand the problem

• Dissect the problem into manageable piecesDissect the problem into manageable pieces

• Design a solutionDesign a solution

• Consider alternatives to the solution and refine itConsider alternatives to the solution and refine it

• Implement the solutionImplement the solution

• Test the solution and fix any problems that existTest the solution and fix any problems that exist

2

Problem SolvingProblem Solving

Many software projects fail because the developer didn't Many software projects fail because the developer didn't really understand the problem to be solvedreally understand the problem to be solved

We must avoid assumptions and clarify ambiguitiesWe must avoid assumptions and clarify ambiguities

As problems and their solutions become larger, we must As problems and their solutions become larger, we must organize our development into manageable piecesorganize our development into manageable pieces

This technique is fundamental to software developmentThis technique is fundamental to software development We will dissect our solutions into pieces called classes and We will dissect our solutions into pieces called classes and

objects, taking an objects, taking an object-oriented approachobject-oriented approach

3

The Java Programming The Java Programming LanguageLanguage

A A programming languageprogramming language specifies the words and symbols specifies the words and symbols that we can use to write a programthat we can use to write a program

A programming language employs a set of rules that dictate A programming language employs a set of rules that dictate how the words and symbols can be put together to form how the words and symbols can be put together to form valid valid program statementsprogram statements

Java was created by Sun Microsystems, Inc.Java was created by Sun Microsystems, Inc. It was introduced in 1995 and has become quite popularIt was introduced in 1995 and has become quite popular It is an object-oriented languageIt is an object-oriented language

4

Java Program StructureJava Program Structure

In the Java programming language:In the Java programming language:• A program is made up of one or more A program is made up of one or more classesclasses

• A class contains one or more A class contains one or more methodsmethods

• A method contains program A method contains program statementsstatements

These terms will be explored in detail throughout the These terms will be explored in detail throughout the coursecourse

A Java application always contains a method called A Java application always contains a method called mainmain

See See Lincoln.javaLincoln.java (page 26)(page 26)

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Java Program StructureJava Program Structure

public class MyProgram

{

}

// comments about the class

class headerclass header

class bodyclass body

Comments can be added almost anywhereComments can be added almost anywhere

6

Java Program StructureJava Program Structure

public class MyProgram

{

}

public static void main (String[] args)

{

}

// comments about the class

// comments about the method

method headermethod headermethod bodymethod body

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CommentsComments

Comments in a program are also called Comments in a program are also called inline inline documentationdocumentation

They should be included to explain the purpose of the They should be included to explain the purpose of the program and describe processing stepsprogram and describe processing steps

They do not affect how a program worksThey do not affect how a program works Java comments can take two forms:Java comments can take two forms:

// this comment runs to the end of the line

/* this comment runs to the terminating symbol, even across line breaks */

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IdentifiersIdentifiers

IdentifiersIdentifiers are the words a programmer uses in a program are the words a programmer uses in a program

An identifier can be made up of letters, digits, the An identifier can be made up of letters, digits, the underscore character (_), and the dollar signunderscore character (_), and the dollar sign

They cannot begin with a digitThey cannot begin with a digit

Java is Java is case sensitivecase sensitive, therefore, therefore Total Total andand total total are are different identifiersdifferent identifiers

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IdentifiersIdentifiers

Sometimes we choose identifiers ourselves when writing a Sometimes we choose identifiers ourselves when writing a program (such as program (such as LincolnLincoln))

Sometimes we are using another programmer's code, so we Sometimes we are using another programmer's code, so we use the identifiers that they chose (such as use the identifiers that they chose (such as printlnprintln))

Often we use special identifiers called Often we use special identifiers called reserved wordsreserved words that that already have a predefined meaning in the languagealready have a predefined meaning in the language

A reserved word cannot be used in any other wayA reserved word cannot be used in any other way

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Reserved WordsReserved Words

The Java reserved words:The Java reserved words:

abstractbooleanbreakbytebyvaluecasecastcatchcharclassconstcontinue

defaultdodoubleelseextendsfalsefinalfinallyfloatforfuturegeneric

gotoifimplementsimportinnerinstanceofintinterfacelongnativenewnull

operatorouterpackageprivateprotectedpublicrestreturnshortstaticsuperswitch

synchronizedthisthrowthrowstransienttruetryvarvoidvolatilewhile

11

White SpaceWhite Space

Spaces, blank lines, and tabs are collectively called Spaces, blank lines, and tabs are collectively called white white spacespace

White space is used to separate words and symbols in a White space is used to separate words and symbols in a programprogram

Extra white space is ignoredExtra white space is ignored A valid Java program can be formatted many different A valid Java program can be formatted many different

waysways Programs should be formatted to enhance readability, Programs should be formatted to enhance readability,

using consistent indentationusing consistent indentation SeeSee Lincoln2.java Lincoln2.java andand Lincoln3.javaLincoln3.java

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Programming Language LevelsProgramming Language Levels

There are four programming language levels:There are four programming language levels:• machine languagemachine language

• assembly languageassembly language

• high-level languagehigh-level language

• fourth-generation languagefourth-generation language

Each type of CPU has its own specific Each type of CPU has its own specific machine languagemachine language

The other levels were created to make it easier for a human The other levels were created to make it easier for a human being to write programsbeing to write programs

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Programming LanguagesProgramming Languages

A program must be translated into machine language A program must be translated into machine language before it can be executed on a particular type of CPUbefore it can be executed on a particular type of CPU

This can be accomplished in several waysThis can be accomplished in several ways

A A compilercompiler is a software tool which translates is a software tool which translates source codesource code into a specific target languageinto a specific target language

Often, that target language is the machine language for a Often, that target language is the machine language for a particular CPU typeparticular CPU type

The Java approach is somewhat differentThe Java approach is somewhat different

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Java Translation and ExecutionJava Translation and Execution

The Java compiler translates Java source code into a The Java compiler translates Java source code into a special representation called special representation called bytecodebytecode

Java bytecode is not the machine language for any Java bytecode is not the machine language for any traditional CPUtraditional CPU

Another software tool, called an Another software tool, called an interpreterinterpreter, translates , translates bytecode into machine language and executes itbytecode into machine language and executes it

Therefore the Java compiler is not tied to any particular Therefore the Java compiler is not tied to any particular machinemachine

Java is considered to be Java is considered to be architecture-neutralarchitecture-neutral

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Java Translation and ExecutionJava Translation and Execution

Java sourcecode

Machinecode

Javabytecode

Javainterpreter

Bytecodecompiler

Javacompiler

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Development EnvironmentsDevelopment Environments

There are many development environments which develop There are many development environments which develop Java software:Java software:• Sun Java Software Development Kit (SDK)Sun Java Software Development Kit (SDK)

• Borland JBuilderBorland JBuilder

• MetroWork CodeWarriorMetroWork CodeWarrior

• Microsoft Visual J++Microsoft Visual J++

• Symantec CaféSymantec Café

Though the details of these environments differ, the basic Though the details of these environments differ, the basic compilation and execution process is essentially the samecompilation and execution process is essentially the same

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Syntax and SemanticsSyntax and Semantics

The The syntax rulessyntax rules of a language define how we can put of a language define how we can put symbols, reserved words, and identifiers together to make a symbols, reserved words, and identifiers together to make a valid programvalid program

The The semanticssemantics of a program statement define what that of a program statement define what that statement means (its purpose or role in a program)statement means (its purpose or role in a program)

A program that is syntactically correct is not necessarily A program that is syntactically correct is not necessarily logically (semantically) correctlogically (semantically) correct

A program will always do what we tell it to do, not what we A program will always do what we tell it to do, not what we meantmeant to tell it to do to tell it to do

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ErrorsErrors

A program can have three types of errorsA program can have three types of errors

The compiler will find problems with syntax and other The compiler will find problems with syntax and other basic issues (basic issues (compile-time errorscompile-time errors))• If compile-time errors exist, an executable version of the program is If compile-time errors exist, an executable version of the program is

not creatednot created

A problem can occur during program execution, such as A problem can occur during program execution, such as trying to divide by zero, which causes a program to trying to divide by zero, which causes a program to terminate abnormally (terminate abnormally (run-time errorsrun-time errors))

A program may run, but produce incorrect results (A program may run, but produce incorrect results (logical logical errorserrors) )

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Introduction to GraphicsIntroduction to Graphics

The last one or two sections of each chapter of the textbook The last one or two sections of each chapter of the textbook focus on graphical issuesfocus on graphical issues

Most computer programs have graphical componentsMost computer programs have graphical components

A picture or drawing must be digitized for storage on a A picture or drawing must be digitized for storage on a computercomputer

A picture is broken down into pixels, and each pixel is A picture is broken down into pixels, and each pixel is stored separatelystored separately

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Representing ColorRepresenting Color

A black and white picture can be stored using one bit per A black and white picture can be stored using one bit per pixel (0 = white and 1 = black)pixel (0 = white and 1 = black)

A color picture requires more information, and there are A color picture requires more information, and there are several techniques for representing a particular colorseveral techniques for representing a particular color

For example, every color can be represented as a mixture For example, every color can be represented as a mixture of the three primary colors Red, Green, and Blueof the three primary colors Red, Green, and Blue

In Java, each color is represented by three numbers In Java, each color is represented by three numbers between 0 and 255 that are collectively called an between 0 and 255 that are collectively called an RGB valueRGB value

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Coordinate SystemsCoordinate Systems

Each pixel can be identified using a two-dimensional Each pixel can be identified using a two-dimensional coordinate systemcoordinate system

When referring to a pixel in a Java program, we use a When referring to a pixel in a Java program, we use a coordinate system with the origin in the upper left cornercoordinate system with the origin in the upper left corner

Y

X(0, 0)

(112, 40)

112

40