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Slide 1 of 64Lecture C

Lesson 3: Conditions and Loops

Unit 1: The if Statement

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The if Statement

The Java if statementhas the following syntax:

if (boolean-condition)

statement;

If the Boolean condition is true, the statement isexecuted if it is false, the statement is s!i""ed

This "rovides #asic decision ma!ing ca"a#ilities

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Tempreture

classTemperature {

static final intTHRESHOLD = 65;

public static voidmainStrin!"# ar!s$ {

%nputRe&uestor input = ne'%nputRe&uestor$;

inttemperature =input(re&uest%nt)Enter t*e temperature+,$;

S-stem(out(println).urrent temperature )/

temperature$;

if temperature 0 THRESHOLD$ S-stem(out(println)%t1s cold in *ere2,$;

3

3

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If statement flow diagram

if (condition)

statement;

condition

condition

statement

statement

true

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oolean !"pressions

The condition of anifstatement must evaluate to a trueor false result

Java has several e$uality and relational o"erators:

%ore com"lex Boolean ex"ressions are also "ossi#le

Operator Meaning

== equal to!= not equal to

< less than

greater than

>= greater than or equal to

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loc# Statements

Several statements can #e grou"ed together into a block

statement

Bloc!s are delimited #y #races

& #loc! statement can #e used wherever a statement is

called for in the Java syntax

if (boolean-condition){

statement1;

statement2;

}

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!"ample % Temperature2

classTemperature4 {

static final intTHRESHOLD = 65;



inttemperature =

input(re&uest%nt)Enter t*e temperature+,$;

S-stem(out(println).urrent temperature )/temperature$;

iftemperature 0 THRESHOLD$ {

S-stem(out(println)%t1s cold in *ere2,$;

S-stem(out(println)ut 'e1ll survive(,$;

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If '' !lse Statement

&nelseclause can #e added to anifstatement to

ma!e it an if-else statement:

if (condition)

statement1;

else

statement2;

If the condition is true, statement1 is executed if thecondition is false, statement' is executed

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!"ample % Temperature3

classTemperature {

static final int7REE8%9:

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If*else flow diagram

if (condition)

statement1;

else

statement2;

conditioncondition

statement2statement2

true

statement1statement1

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+ested If statements

Since an (If) statement is a statement, it can a""ear inside

another if statement*

if (condition1)

if (condition2)

statement;

It can also a""ear in an (else) clause

if (condition1) statement1;

else if (condition2)

statement2;

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+ested If !"ample?? Reads 4 inte!ers and compares t*em

class.ompareE@ample {



inta = input(re&uest%nt)7irst number+,$;

intb = input(re&uest%nt)Second number+,$;

ifa 2= b${ ifa A b$

S-stem(out(printlna/, is !reater,$;

else

S-stem(out(printlnb/, is !reater,$;

3else

S-stem(out(println)t*e numbers are e&ual,$;

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Chec#ing ,our Input +hen re$uesting in"ut from the user, !ee" in mind that the in"ut may #e invalid*

It is good "ractice to chec! the validity of user in"ut

intnumberOf%tems =

input(re&uest%nt)Enter number of items+,$;

ifnumberOf%tems 0 B$ { S-stem(out(println

)9umber of items must be positive2,$;

3 else{

doubleprice = numberOf%tems C %TE

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Lesson 3: Conditions and Loops

Unit ': Boolean x"ressions

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Logical -perators

Boolean ex"ressions may #e com#ined using logical

operators

There are three logical o"erators in Java:

They all ta!e Boolean o"erands and "roduce Booleanresults

-ogical ./T is unary 0one o"erand, #ut logical &.2 and

/3 are #inary 0two o"erands

Operator Operation

! LogicalNOT&& LogicalAN

Logical O"

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Logical +-T

The logical ./T is also called logical negation or logical

com"lement

If ais true, !ais false if ais false, then !ais true

-ogical ex"ressions can #e shown using truth tables

a !a

false true

true false

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Logical .+/

The ex"ression a && #is true if #oth aand#are true,

and false otherwise

Truth ta#les show all "ossi#le com#inations of all terms

a # a && #

false false false

false true false

true false falsetrue true true

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Logical -0

The ex"ression a #is true if aor bor #oth are true,

and false otherwise

a # a #

false false false

false true true

true false truetrue true true

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Logical -perators

-ogical o"erators are used to form more com"lex logical

ex"ressions

-ogical o"erators have "recedence relationshi"s #etween

themselves and other o"erators

ifa0 FF aG42=B$

S-stem(out(println

)T*e input s*ould be an even even number2,$;

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Logical -perators

4ull ex"ressions can #e evaluated using truth ta#les

a < 1 a$2!=% a

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oolean ariales

Boolean ex"ressions can #e assigned to Boolean

varia#les

Boolean varia#les are Boolean ex"ressions

#oolean# c;

# = (' > 1);

c = ('>1) && ('

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!"ample % 0ightTriangle?? Receives t*e len!t* of t*e ed!es of a trian!le

?? and determine if t*is is a ri!*t trian!le

classRi!*tTrian!le {



floata = input(re&uest%nt)Ed!e+,$;

float b = input(re&uest%nt)Ed!e4+,$; floatc = input(re&uest%nt)H-potenuse+,$;

booleantest = aCa/bCb == cCc;

iftest$

S-stem(out(println)%t1s a ri!*t trian!le,$;

else

S-stem(out(println)%t1s not a ri!*t trian!le,$;

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Lesson 3: conditions and loops

Unit 56: The while Statement

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The while statement

& while statementhas the following syntax:

34ile (condition)

statement;

If the condition is true, the statement is executed thenthe condition is evaluated again

The statement is executed over and over until the

condition #ecomes false

If the condition of a34ilestatement is false initially, thestatement is never executed

Therefore, we say that a34ilestatement executes 7ero

or more times

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hile statement flow diagram

34ile (condition)

statement;

conditioncondition

statementstatement

true

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!"ample % Counter

?? .ounts from to 5

class.ounter { static final intL%%T = 5;


intcount = ; '*ilecount 0= L%%T$ {

S-stem(out(printlncount$;

count = count / ;

3

S-stem(out(println)done,$;

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Slide 2$ of 64Lecture C

!"amples % actors?? :ets an inte!er and prints its factors

class7actorsE@ample {



inta = input(re&uest%nt)Enter a number+,$;

inti = ;

S-stem(out(println)T*e divisors of )/a/, are+,$; '*ile i 0= a$ {

ifaGi == B$ {

S-stem(out(printlni$;

3

i = i / ;

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Slide 2& of 64Lecture C

Infinite Loops

The #ody of a34ileloo" must eventually ma!e the

condition false If not, it is an infinite loop, which will execute until the user

interru"ts the "rogram

This is a common ty"e of logical error 88 always dou#le

chec! that your loo"s will terminate normally

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Slide 2( of 64Lecture C

!"ample % oreer

?? T*is pro!ram contains an infinite loop

class7orever { static final intL%%T = 45;


intcount = ; '*ilecount 0= L%%T$ {

S-stem(out(printlncount$;

count = count ;

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Slide 3) of 64Lecture C


Unit 9: %ore conditionals

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The Conditional -perator

Java has a conditional o"erator that evaluates a Boolean

condition that determines which of two ex"ressions isevaluated

The result of the chosen ex"ression is the result of the

entire conditional o"erator

Its syntax is:

condition5 expression16

expression2

If the conditionis true, expression1is evaluated if it isfalse, expression2is evaluated

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It is similar to an if8else statement, exce"t that it is an

ex"ression that returns a value

4or exam"le:

If ais greater that#, then ais assigned toma'otherwise,#is assigned toma'

The conditional o"erator is ternary, meaning it re$uires

three o"erands

intma@ = a A b$ I a + b;

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&nother exam"le:

If conte$uals 1, "ime"is "rinted, otherwise

"imes"is "rinted

*+stem,ot,./intln (78o/ c4ane is 79 cont 9

((cont == 1) 5 7ime76 7imes));

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.nother Selection Statement

The ifand the if-elsestatements are selection

statements, allowing us to select which statement to"erform next #ased on some Boolean condition

&nother selection construct, called the switch statement,

"rovides another way to choose the next action

The switchstatement evaluates an ex"ression, then

attem"ts to match the result to one of a series of values

xecution transfers to statement list associated with the

first value that matches

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The

s3itc4Statement

The syntax of the switch statement is:

switch (expression) {

case value1:

statement-list1

case value2:

statement-list2

case

}

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The s3itc4Statement

The ex"ression must evaluate to an integral value, such

as an integer or character

The breakstatement is usually used to terminate the

statement list of each case, which causes control to um"

to the end of the switchstatement

& defaultcase can #e added to the end of the list ofcases, and will execute if no other case matches

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The s3itc4Statement

?CC

C > client t*at enables -ou to connect to t*eC banJ server and maJe remote banJin! operations(((

C?

public class anJ.lient {

public static final intK%E>L>9.E = ;

public static final intK%ES>K%9:S = 4;

public static final int.>SHTR>9S7ER = ;

public static final intK%EL>STOT%O9S = M;

?? (((

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The s3itc4Statement

?? %nside t*e main loop of t*e client+

intoption =%nputRe&uestor(re&uent%nt)Enter -our c*oice+,$;

s'itc*option$ {

caseK%E>L>9.E+

s*o'alance$;

breaJ;

caseK%ES>K%9:S+

s*o'Savin!s$;

breaJ;

default+ output(s*o'essa!e)9o suc* option2,$;

3

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Unit ;: Shorthand /"erators

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Shorthand -perators

%any o"erations are very commonly used

Java has shorthand notations for these increment and decrement o"erators

assignment o"erators

@ = @ / ;

sum = sum / @;

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The Increment and /ecrement -perators

The increment operator099 adds one to its integer or

floating "oint o"erand

The decrement operator0-- su#tracts one

The statement

is essentially e$uivalent to

cont99;

cont = cont 9 1;

-

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The increment and decrement o"erators can #e a""lied

in "refix 0#efore the varia#le or "ostfix 0after the varia#leform

+hen used alone in a statement, the "refix and "ostfix

forms are #asically e$uivalent* That is,

is e$uivalent to

cont99;

99cont;

Th I d / -

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+hen used in a larger ex"ression, the "refix and "ostfix

forms have a different effect

In #oth cases the varia#le is incremented 0decremented

But the value used in the larger ex"ression de"ends on

the form

:'./essions O.e/ation ale Of e'./ession

count++ add 1 old value

++count add 1 new valuecount-- subtract 1 old value

--count subtract 1 new value

Th I t d / t - t

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If contcurrently contains 9;, then

assigns 9; to totaland 9< to cont

If contcurrently contains 9;, then

assigns the value 9< to #oth totaland cont

total = count//;

total = //count;

Th I t d / t - t

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If sum contains ';, what does this statement "rint=

>rints the following result:

2 2 2 2

sum contains '< after the line is com"lete

S-stem(out(println sum// / N N/

//sum / N N/

sum / N N/

sum$;

. i t - t

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.ssignment -perators

/ften we "erform an o"eration on a varia#le, then store

the result #ac! into that varia#le

Java "rovides assignment operatorsthat sim"lify that

"rocess

4or exam"le, the statement

is e$uivalent to

sum /= value;

sum = sum / value;

. i t - t

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There are many such assignment o"erators, always

written as op=, such as:

O.e/ato/ :'am.le :ialent to

+= x+=y x = x + y

-= x-=y x = x - y

*= x*=y x = x * y

/= x/=y x = x / y

%= x%=y x = x % y

. i t - t

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The right hand side of an assignment o"erator can #e a

com"lete ex"ression The entire right8hand ex"ression is evaluated first, then

com#ined with the additional o"eration

Therefore

/eslt ?= total-@N;

is e$uivalent to

result ?= total%9;

/eslt = /eslt ? (total-@N);

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Unit 5

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ore 0epetition Constructs

In addition towhileloo"s, Java has two other

constructs used to "erform re"etition:

the dostatement

the forstatement

ach loo" ty"e has its own uni$ue characteristics

?ou must choose which loo" ty"e to use in each situation

The d Statement

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The doStatement

The do statementhas the following syntax:

do

statement

34ile (condition);

The statementis executed until the condition#ecomes

false

It is similar to a whilestatement, exce"t that its

termination condition is evaluated after the loo" #ody

The d Statement

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The doStatement

The !ey difference #etween a doloo" and a whileloo"

is that the #ody of the doloo" will execute at least once

If the condition of a whileloo" is false initially, the #ody

of the loo" is never executed

&nother way to "ut this is that a whileloo" will execute

7ero or more times and a doloo" will execute one or

more times

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/o Statement !"ample

?? :ets an inte!er and prints its factors

class>v!E@ample {

public static voidmainStrin!"# ar!s${


double@ sum=B count=;

do{

@ = input(Re&uestDouble)9e@t number+,$;

sum /= @;

count//;

3 '*ile@ 2= B$;

?? B is a fla! indicatin! end of input S-stem(out(println)T*e avera!e is )/sum?count$;

3

3

The do Statement flow diagram

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The doStatement flow diagram

statement

condition

false

true

The fo/ Statement

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The fo/Statement

%any loo"s have a common "attern, ca"tured #y the for

statement The syntax of the for loopis

fo/ (intialiation; condition; increment)

statement;

This is e$uivalent to

initialiBation;

34ile (condition) {

statement;

inc/ement;

}

The fo/ Statement: e"amples

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The fo/Statement: e"amples

xam"les:

forintcount=; count 0 P5; count//$ {

S-stem(out(println count$;

3

forintnum=; num 0= ma@; num = num C 4$ {

S-stem(out(println )9e@t po'er of 4+ )/ num$;

3

The fo/ Statement

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The fo/Statement

The initiali7ation is always "erformed once

The condition of a forstatement is testedpriorto

executing the loo" #ody 0li!e in the whilestatement

Therefore, a forloo" will execute 7ero or more times

4or loo"s are well suited for cases where the num#er of

iterations is !nown #eforehand

The increment is executed after each iteration of the loo"

-mitting parts in a for Statement

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-mitting parts in a forStatement

ach ex"ression in the header of a forloo" is o"tional If the initiali7ation is left out, no initiali7ation is "erformed

If the condition is left out, it is always considered to #e true, and

therefore ma!es an infinite loo"

If the increment is left out, no increment o"eration is "erformed

Both semi8colons are always re$uired

for;;$ {?? an infinite loop

S-stem(out(println )beep,$;

3

?? compute a value count for; count 0 ma@ ; count // $ {

S-stem(out(println count$;

3

The fo/ Statement flow diagram

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The fo/Statement flow diagram

statement

conditionfalse

true

initialization

increment

lti li ti T l ! l

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ultiplication Tale !"ample

classultiplicationTable {


forint Q= ; Q 0= B ; Q//$ {

forint J= ; J 0= B ; J//$

S-stem(out(printQCJ$;

S-stem(out(println$; 3

3

3

The #/eaC and contine statements

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The#/eaCand continestatements

The breakstatement, which we used with switch

statements, can also #e used inside a loo" +hen the breakstatement is executed, control um"s to

the statement after the loo" 0the condition is not

evaluated again

& similar construct, the continuestatement, can also #eexecuted in a loo"

+hen the continuestatement is executed, control

um"s to the end of the loo" and the condition is

evaluated

# d C ti ! l

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rea# and Continue !"ampleclass>v!E@ample4 {


%nputRe&uestor in = ne'%nputRe&uestor$; double@ sum = B; count = B;

'*iletrue${

@ = in(Re&uestDouble$;

if@ == B$breaJ;

if@ 0 B$ {

S-stem(out(println)Onl- positive numbers2,$;

continue;

3

sum /= @ ;

count // ;

3 ?? continued on ne@t pa!e

# d C ti ! l 27

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rea# and Continue !"ample 27

*+stem,ot,./intln(0T4e ae/ae is 09sm?cont);

}

}

h d + d I d t ti 8

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h, do e +eed Indentation8

class-ster- {

public static voidmainStrin!"# ar!s$ {%nputRe&uestor in = ne'%nputRe&uestor$;

int dimension =

in(re&uest%nt)

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