CS101/CS101E
Todaysclass
Anoverviewofchapters13 ReviewforExam1
Spring2007 Stop me if you want me to go over something in moredetail!
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Chapter1
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Intro
Computersthinkinbits(1or0)
00101001=81
Eightbitsperbyte
1024bytes=1Kb 1024Kb=1Mb 1024Mb=1Gb
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Computerorganization
CPU=brain Microprocessor:computeronasinglechip Network:whentwoormorecomputersareplugged intooneanother
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Software
OS: the program that manages a computers resources Program: a sequence of instructions that performs sometask
Performing an instruction is called executing an instruction
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Compilation
Translator:
Machinelanguage: Compiler:
translatesaprogramfromonelanguagetoanother theonesandzerosthatacomputerunderstands Alowlevellanguage! a translator which typically translates a highlevel language into a lowlevelone Javaisahighlevellanguage Bytecode is like machine language, but not tied to a specific machine CalledaJavaVirtualMachine(JVM)
JavascompilertranslatesJavacodeintobytecode
AJavabytecodeinterpreterisusedtoexecutethebytecode
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Terminology
Abstraction
Similarobjectsexhibitsimilarbehavior Theabilitytodothesamethingonmanyobjects
Encapsulation
Notrevealinghowthemethoddoesitswork ConsiderString.substring()
Modularity
Dividingcodeintosmallerpieces(modules),eachoneofwhich iseasiertocode
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OOPTerminology
OOP(ObjectOrientedProgramming)languages:
A(primitive)typeisthebasicunitofstorageinJava
Abstractthingsintotheclassmethods Encapsulatecodeinsidetheclassmethods Useadditionalmethodsformodularity Atypeisatemplateforavariable
A classis composed of types (or other classes) as well as methods
Creating a variable/object from a type/class is called instantiatingthetype/class
Aclassisatemplateforanobject
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Problemsolvingsteps
Analysis
Whatneedstobedone? Howisitgoingtobedone? Makeitso! Doesitworkcorrectly?
Design
Implementation
Testing
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Chapter2
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Readableprograms
CommentsareEnglishtext
Havea//beforetheminaJavafile /**/ /***/
Blanklinesmakeaprogrameasiertoread Indentation helps humans identify which code is withinthemethod KeywordshavespecialmeaningsinJava
Examples:int,double,class,static,public
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Identifiers
Identifiers:programmerdefinednames
Forclasses,variables,methods,etc. Cannotbeakeyword Muststartwithaletter(or_or$) Cancontainnumbersalso(butnotasthefirstcharacter)
Goodidentifiers:radius,width,position Badidentifiers:x,y,q, the_really_really_long_variable_name_hi_mom
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Computerbugs
Abugisanerrorintheprogram Todebugistoremovebugs
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Javaclasses
Theclasskeywordisusedtostartaclass declaration
Canbemadepublic(forthiscourse,alwaysdoso) Justasatypeisatemplateforavariable
Aclassisatemplateforanobject
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Javamethods
Allmethodshavethefollowingsyntax:
modiferstypename(parameters){statements}
Properties ofthe method
Type thatit returns
Aname forthe method
Anynumber (includingzero) ofparameters
Thebodyof themethod (canbeempty)
publicstatic
void
main
(String[]args)
{...}
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Programexecution
Javastartsexecutingaprogramatthebeginningof themain()method Braces { } are used to specify where a method beginsandends A statement ends when a semicolon is encountered
Astatementcanspanmultiplelines
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Miscstuff
A literal character string is a sequence of characters enclosed by doublequotes System is the Java class that allows you to access parts of the computersystem
System.in:accesstothekeyboard System.out:accesstothemonitor GivenStrings,selectamethodvia:s.substring() Itmeanssomethingiswrong
Periodisusedforselection:Math.round
AnexceptioniswhenJavapanics
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Escapesequences
Java provides escape sequences for printing special characters
\b backspace \n newline \t tab \rcarriagereturn \\ backslash \"doublequote \ singlequote
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Primitivevariabletypes
Javahas8(orso)primitivetypes:
float double boolean char byte short int long
realnumbers twovalues:trueandfalse asinglecharacter integernumbers
Alsothevoidtype Canmakeavariablefinal
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Symbolicnamesvs.literalvalues
Whichiseasiertoenter:
Math.PI 3.141592653589793
Enteringasymbolicname(i.e.aconstant)reduces chancesoferrors Itallowsforchangingtheconstantlateron Areusuallyfinal
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Referencesandvariables
Avariableisanactualspotinmemorythatholdsa A (primitivetype)value reference is a memory address that points to anotherspotinmemorywheretheobjectis Variables defined in a class are initialized to a defaultvalue Variablesdefinedinamethodarenotinitializedto adefaultvalue
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Math
Standardoperators:+*/ Notethat/canbeeitherintegerdivisionorfloating pointdivision %computestheremainder(akamodulus) Can provide numbers in decimal or scientific notation
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Expressions
Evaluatinganexpressionyieldsaresultandatype
Binaryoperatorhastwooperands
Example:4/3yields1oftypeint Example:3.5*2.0yields7.0oftypedouble Example:3+4,6*3,etc. Leftoneisevaluatedfirst Example:3,etc.
Unaryoperatorhasoneoperand
Operatorshaveprecedence
Forexample,*and/areevaluatedbefore+and
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Overflow
Consider:
byteb=100; b=b*100;
Abytecanonlyholdupto+127 Thisiscalledoverflow
Javadoesnottellyouthatthishappened!
Underflow:b=b*100;
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Operators
Assignment:= Increment(++)anddecrement() Consider:
inti=5; System.out.println(i++); System.out.println(i); inti=5; System.out.println(++i); System.out.println(i);
Thereare4waystoadd1toanint:
i=i+1; i+=1; i++; ++i
Therearemanysuch compoundoperators
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Casting
Castingconvertsonetypetoanother Example: intx=1; System.out.println((double)x); doubled=3.4; System.out.println((int)d);
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Scannerclass
Creatingone:
Scannerstdin=newScanner(System.in)
Methods:
DontuseScanner.create()! publicintnextInt() publicshortnextShort() publiclongnextLong() publicdoublenextDouble() publicfloatnextFloat() publicStringnext() publicStringnextLine() publicbooleanhasNext()
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References
Anobjectvariableisreallyareferencetothatobject nullrepresentsanobjectvariablethatpointstonothing Oncenothingpointstoanobject,Javaautomaticallydeletes thatobject
Calledgarbagecollection Onlythereference(whereitpointsinmemory)isfinal Thevaluesintheobjectcanchangeviamembermethods
Afinalobjectvariable:
Weuseconstructorstocreateobjects
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Strings
AStringisasequenceofcharacters The+operatorconcatenatestwoStrings The+=operatorappendsaString Firstcharacterhasindex0 AStringcanneverbemodifiedoncecreated!
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Stringmethods
length() substring() indexOf() lastIndexOf() charAt() trim() valueOf()
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Rectangleclass
Represents a Rectangle (for displaying on the screen) Hasheight,width,xposition,andyposition
Mainconstructortakesinthese4arguements
setLocation()changestheposition resize()changestheheightandwidth
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Cha...