2.Javalanguagebasics:Condi&on,1Darray,andloop

MinhaengLee

Contents

•   Cas7ngandconversion

•   Condi7onalStatement(if)•   Loop•   Switch•   Prac7ce(Mul7plica7onTable!)•   Homework

Cas7ng

•   Datatransferbetweentwodifferenttypes–  E.g.fromintegertofloat/double–  Use“(<type>)”beforesourcevariable

•   E.g.doubletarget=(double)iAmInteger;

–  Becarefulwhenbiggeronetosmallerone•   Datalossexpected

–   Float(3.4)toInteger(3)•   E.g.cas7ngfromdoubletoshort

–   3.141592(double)à3(int)

Cas7ng(prac7ce)

•   inta;floatb;doublec;booleand;

•   inttodouble:(double)a•   doubletofloat:(float)c•   floattoint:(int)b•   inttoboolean:(boolean)a(notpossible)

UsefulClassTypes

•   String–  Usedoublequota7on“”–  Canstoresequenceofcharacters–  Concatena7onusing+

•   LONG=“small”+“small”;(LONG=“smallsmall”)

•   FromothertypestoString–  UsetoString–  Everyclasshave–  EveryclasscanbeprintedasStringtype

Conversion•   InbuiltexplicitmethodinJava–   IntegertoString–   String“1000”toInteger1000

•   FromStringtonumber–   <Integer/Float/Double>.parse<Int/Float/Double>();–   e.g.doubled=Double.parseDouble(stringValue);

•   FromnumbertoString–  UsetoString()thateveryclasshave

Conversion(prac7ce)•   inttoString Integer.toString(value)•   floattoString Float.toString(value)•   doubletoString Double.toString(value)•   Stringtoint Integer.parseInt(stringValue)•   Stringtofloat Float.parseInt(floatValue)•   Stringtodouble Double.parseInt(doubleValue)

•   Integertoint (int)IntegerValue•   Floattofloat (float)FloatValue•   Doubletodouble (double)DoubleValue

MathNota7on•   Operator

–   +:plus–   -:minus–   *:mul7plica7on–   /:division–   %:remainingvalues(4%3:1,10%2:0)

•   Mathfunc7ons–   Math.<something>();–   Math.sqrt(var);–   Math.round(var);–   Math.ceil(var);–   Math.floor(var);–   Math.pow(var,var);–   Etc.

Shortnota7on

•   UsedinC,C++,Java•   ++,--–  a++:a=a+1–  a--:a=a-1

•   +=,*=,/=,-=–  a+=1:a=a+1–  A*=10:A=A*10–  …

Quickprac7ce

Booleantype

•   Shouldbetrueorfalse•   0=false,otherwise=truebutspecificbooleanresultissuggested

•   Cancompareonlytwocompa7blevariables

BooleanOperators

hjp://faculty.uoit.ca/sar7pi/courses/OO/f12/2.slides/ch05-decisions/ch05-HTML/ch05/images/boolean_operators.png

If,Ifelse,andelse•   If(<condi*on>)<statement>;

–   Ifgiven<condi7on>istrue,thenexecuteonlyone<statement>

•   if(<condi*on>){<statements>}–   Ifgiven<condi7on>istrue,thenexecute<statements>

•   if(<condi*on>){<statement1>}else{<statements2>}–   Ifgiven<condi7on1>istrue,thenexecute<statements1>,otherwise

executeonly<statements2>

•   if(<condi*on1>){<statements1>}elseif(<condi*ons2>){<statements2>}else{<statements3>}–   Ifgiven<condi7on1>istrue,thenexecute<statements1>,otherwise

execute<statements2>if<condi7on2>istrue,otherwiseexecute<statements3>

If,Ifelse,andelse

If,ifelse,andelse(prac7ce!)

•   Peoplecandrinkbeerwhentheyareover20•   Peoplecandrivewhentheyareover14•   Writeacodethatprintwhatpeoplecando.•   E.g.15->“candrivebutcannotdrinking”,21->”candriveand

drinking”,10->“cannotneitherdrivenordrinking”•   Usenestedif

•   Printgradefrom“A”…to“F”•   Fromonesingleintegervalue(0–100)•   Useif,ifelse,andelse.•   90–100:A•   80–90:B•   70–80:C•   60–70:D•   0–60:F

Prac7ce1

Prac7ce2

14

20

0

100age

Array•   Storemul7pledatainasinglevariable•   []indicates1D-array•   <Type>[]<variablename>=new<Type>[<size>];•   Needini7aliza7on–  Usenewkeywordtoindicatememoryalloca7on–   c.f.singlevariabledoesn’tneedtodoit

•   Example:–   Singleint:inta;–  Mul7pleints:int[]a=newint[10];

Array-access•   intarray:int[]a=newint[10];•   Stringarray:String[]strArray=newString[10];

•   Accessthefirstelement–   Indexbeginswith0–   Examples

•   Store10tothefirstone:a[0]=10;•   Getsecondnumberandstore:b=a[1];•   Printthefirstone:System.out.println(a[0]);

•   Usefulproperty:length–   Returnsthelengthofarray–   Example:a.length

Loop•   While

–   While(<condi7on>){<statement>}–   Execute<statement>while<condi7on>istrue–   Sequence:<condi7on>-<statement>-<condi7on>-<statement>…

•   Do-While–   Do{<statement>}While(<condi7on>)–   SimilartoWhilebutexecute<statement>atleastone7me.–   Sequence:<statement>-<condi7on-<statement>-<condi7on>…

•   For–   For([init];<condi7on>;[incremental]){<statement>}–   Sequence:[init]-<condi7on>-<statement>-[incremental]-

<condi7on>-<statement>-[incremental]-….

•   Breakneeded

Loop:while

12

3

1 2 3 2 3

Loop:Do-while

12

3

1 2 3 2 3

Loop:for

1 2 4 3 2

12

3

4

4 3

Let’sprac7ce:Timestable•   Timestableforonenumber(ex.2)•   Usingoneloop•   Expectedoutput:

–   2x1=2–   2x2=4–   2x3=6–   …

•   Timestableformul7plenumber(ex2–5)•   Usingnestedloop•   Expectedoutput:

–   2x1=2,3x1=3,4x1=4,5x1=5–   2x2=4,3x2=6,4x2=8,5x2=10–   ….

breakandcon7nue

•   Break–  Usedinloop–  Stopcurrentloop

•   ConJnue–  Usedinloop–  Skiprestofstatementandgonextitera7on

Example

Switch•   Similartomul7pleifelsestatement•   Onlypossiblewhenweuseintvariableandcondi7onalvaluecheck

whetheritisequal•   Executefromcertaincasetotheend

•   Switch<variable>{–   Case<case1>:

•   <statement1>;•   break;

–   Case<case2>:•   <statement2>;•   …•   break;

–   Default:•   <defaultstatement>;

•   }

If<variable>isequalto<case1>thenexecute<statement1>ElseIf<variable>isequalto<case2>thenexecute<statement2>…ElseExecute<defaultstatement>

Switch

ExactlySame?

Homework1.

•   Mul7-line7mestable(2–9)•   Usingtriplenestedloops–  2to5fortoprow–  6to9forlowerrow

•   Omitsimilarnumbermul7plica7on•   Using“if”and“else”ontopofpreviousone–  E.g.1x1,2x2,3x3…soon.