© 2006 pearson education 1 obj: cont 1.3 and 1.4, to become familiar with identifiers and to...

© 2006 Pearson Education11

Obj:Obj: cont 1.3 and 1.4, to become familiar cont 1.3 and 1.4, to become familiar with identifiers and to understand how with identifiers and to understand how programming languages workprogramming languages work

HW:HW: p.51 #1.8 – 1.9 (Short Answers) p.51 #1.8 – 1.9 (Short Answers)

Chapter 1 Test in two class daysChapter 1 Test in two class days

Do Now:Do Now:

How is the program on p.33 different from How is the program on p.33 different from the program on p.27? the program on p.27?

C1 D6C1 D6


IdentifiersIdentifiers

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

Some identifiers are already definedSome identifiers are already defined Ex: class, public, static, void, main, println, Ex: class, public, static, void, main, println,

String,…String,…

Some are made up by the programmer:Some are made up by the programmer: Ex: LincolnEx: Lincoln


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

Identifiers cannot begin with a digitIdentifiers cannot begin with a digit

Java is Java is case sensitivecase sensitive - - Total, total, Total, total, andand TOTAL TOTAL are different identifiersare different identifiers

By convention, Java programmers use By convention, Java programmers use different case styles for different types of different case styles for different types of identifiers, such asidentifiers, such as title case title case for class names - for class names - LincolnLincoln

upper caseupper case for constants - for constants - MAXIMUMMAXIMUM


IdentifiersIdentifiers

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

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


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

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


Reserved WordsReserved Words The Java reserved words are listed in your The Java reserved words are listed in your

text on p.31text on p.31 You do not need to You do not need to memorizememorize this list, but this list, but

you should know whether or not a word is you should know whether or not a word is on this list.on this list.

For example, you should know that you For example, you should know that you cannot use the word “while” other than for cannot use the word “while” other than for it’s pre-defined use.it’s pre-defined use.


White SpaceWhite Space

Spaces, blank lines, and tabs are called Spaces, blank lines, and tabs are called white spacewhite space

White space is used to separate words White space is used to separate words and symbols in a programand symbols in a program

Extra white space is ignoredExtra white space is ignored

A valid Java program can be formatted in A valid Java program can be formatted in many waysmany ways


Programs should be formatted to enhance Programs should be formatted to enhance readability, using consistent indentationreadability, using consistent indentation

SeeSee Lincoln2.java (page 33) (page 33)

SeeSee Lincoln3.java (page 34) (page 34) These are both the same exact program These are both the same exact program

as on p.27, but they are more difficult for a as on p.27, but they are more difficult for a human to read.human to read.


Language LevelsLanguage Levels There are four programming language levels:There are four programming language levels:

machine languagemachine language assembly languageassembly language high-level language (ex: Java, understandable by high-level language (ex: Java, understandable by

programmers)programmers) fourth-generation language (doesn’t require fourth-generation language (doesn’t require

knowledge of a programming language)knowledge of a programming language)

See p.36See p.36


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 The other levels were created to make it easier for a human being to read and write easier for a human being to read and write programsprograms


Programming LanguagesProgramming Languages

A program must be translated into A program must be translated into machine language before it can be machine language before it can be executed on a particular type of CPUexecuted 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 is a software tool which translates translates source codesource code into a specific into a specific target languagetarget language


JCreator, our editor, is actually an IDE JCreator, our editor, is actually an IDE ((Integrated Development EnvironmentIntegrated Development Environment))

It combines an editor, a compiler, and It combines an editor, a compiler, and other Java support tools.other Java support tools.

Other examples of IDEs are NetBeans and Other examples of IDEs are NetBeans and Eclipse. Eclipse.


Java TranslationJava Translation

Java sourcecode

Machinecode

Javabytecode

Javainterpreter

Bytecodecompiler

JavaCompiler

(ex: JCreator)


Syntax and SemanticsSyntax and Semantics

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

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


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

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


ErrorsErrors

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

The compiler will find syntax errors and The compiler will find syntax errors and other basic problems (other basic problems (compile-time errorscompile-time errors))

If compile-time errors exist, an executable If compile-time errors exist, an executable version of the program is not createdversion of the program is not created


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

A program may run, but produce incorrect A program may run, but produce incorrect results, perhaps using an incorrect formula results, perhaps using an incorrect formula ((logical errorslogical errors) )


Basic Program DevelopmentBasic Program Development

errors

errors

Edit andsave program

Compile program

Execute program andevaluate results


If time:If time:

Do p.52 #1.1Do p.52 #1.1

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