durga core java book

7/22/2019 Durga Core Java Book

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Language Fundamentals1. Identifiers2. Reserved words3. Data types4. Literals5. Arrays6. Types of variabless7. ar ar! "et#od$. %ain "et#od&. 'o""and line ar!("ents1). *ava +odin! standardsIdentifier: A na"e in ,ava pro!ra" is +alled identifier. It "ay be +lass na"e- "et#od na"e-

variable na"e and label na"e.

Example:

Rules to define java identifiers:

Rule 1:T#e only allowed +#ara+ters in ,ava identifiers are

1/ a to 02/ A to 3/ ) to &4/ 5/

Rule 2:If we are (sin! any ot#er +#ara+ter we will !et +o"pile ti"e error.

Example:

1/ totaln("bervalid2/ Totalinvalid

Rule 3:identifiers are not allowed to starts wit# di!it.

Example:

1/ A'123valid2/ 123A'invalid

Rule 4:,ava identifiers are +ase sensitive (p +o(rse ,ava lan!(a!e itself treated as +ase sensitive

lan!(a!e.


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Example:

+lass Test

int n("ber81)9int :("ber82)9

int :;%


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Reserved %ords:

In ,ava so"e identifiers are reserved to asso+iate so"e f(n+tionality or "eanin! s(+#type of reserved identifiers are +alled reserved words.

'iagram:

Reserved %ords for data t(pes:

1/ byte2/ s#ort3/ int4/ lon!5/ float6/ do(ble7/ +#ar$/ boolean

Reserved %ords for flo% $ontrol:

1/ if2/ else3/ swit+#4/ +ase5/ defa(lt6/ for7/ do


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$/ w#ile&/ brea?1)/+ontin(e11/ret(rn

)e(%ords for modifiers:

1/ p(bli+2/ private3/ prote+ted4/ stati+5/ final6/ abstra+t7/ syn+#roni0ed$/ native&/ stri+tfpB1.2 version/1)/transient11/volatile

)e(%ords for ex$eption #andling:

1/ try2/ +at+#3/ finally4/

t#row

5/ t#rows6/ assertB1.4 version/

*lass related +e(%ords:

1/ +lass2/ pa+?a!e3/ i"port4/ eEtends5/ i"ple"ents6/

interfa+e

!,je$t related +e(%ords:

1/ new2/ instan+eof3/ s(per4/ t#is

-oid return t(pe +e(%ord:

If a "et#od wont ret(rn anyt#in! +o"p(lsory t#at "et#od s#o(ld be de+lared wit# t#evoid ret(rn type in ,ava b(t it is optional in 'FF.


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1/ void.nused +e(%ords:

goto 'reate several proble"s in old lan!(a!es and #en+e it is banned in ,ava.*onst: ;se final instead of t#is.

y "ista?e if we are (sin! t#ese ?eywords in o(r pro!ra" we will !et +o"pile ti"eerror.

Reserved literals:

1/ tr(e val(es for boolean data type.2/ false3/ n(ll defa(lt val(e for ob,e+t referen+e.

Enum:

T#is ?eyword introd(+ed in 1.5v to define a !ro(p of na"ed +onstantsExample:

en(" eer

GH- R'- G- H9

=

/ote:All reserved words in ,ava +ontain only lower+ase alp#abet sy"bols.

:ew ?eywords are

Ctri+tfp1.2

Assert1.4


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'ata t(pes:


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Example:

byte b81)9

byte b2813)9JJ'.


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4/ float follows sin!le pre+ision. 4/ do(ble follows do(ble pre+ision.,oolean data t(pe:

Ci0e :ot appli+able Bvirt(al "a+#ine dependent/Ran!e :ot appli+able b(t allowed val(es are tr(e or false.

"#i$# of t#e follo%ing ,oolean de$larations are valid&

Example 1:

boolean b8tr(e9

boolean b8Tr(e9JJ'.


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Do(ble $ bytes 1.7e3)$ to

1.7e3)$

Do(ble ).)

oolean :ot appli+able :otappli+ableBb(t

allowed val(es

tr(eOfalse/

oolean false

'#ar 2 bytes ) to 65535 '#ara+ter )Brepresents

blan? spa+e/

T#e defa(lt val(e for t#e ob,e+t referen+es is Kn(ll.Literals:

Any +onstant val(e w#i+# +an be assi!ned to t#e variable is +alled literal.Example:

Integral Literals: Hor t#e inte!ral data types Bbyte- s#ort- int and lon!/ we +an spe+ify literal

val(e in t#e followin! ways.

1/ 'e$imal literals:Allowed di!its are ) to &.Example: int E81)9

2/ !$tal literals: Allowed di!its are ) to 7. Literal val(e s#o(ld be prefiEed wit# 0ero.Example:int E8)1)9

3/ exa 'e$imal literals: T#e allowed di!its are ) to &- A to . Hor t#e eEtra di!its we +an(se bot# (pper +ase and lower +ase +#ara+ters. T#is is one of very few areas w#ere ,avais not +ase sensitive. Literal val(e s#o(ld be prefiEed wit# oEBor/oP.

Example: int E8)E1)9 T#ese are t#e only possible ways to spe+ify inte!ral literal.

"#i$# of t#e follo%ing are valid de$larations&

1/ int E8)7$69JJ'.


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Example:

int E81)9Bvalid/

lon! l81)L9Bvalid/

lon! l81)9Bvalid/

int E81)l9JJ'.


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Example:

do(ble d81)e29JJ881)U1)2Bvalid/

Cyste".o(t.printlnBd/9JJ1))).)

float f81)e29JJ'.


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Y Cin!le V(ote

Y Do(ble V(ote

YY a+? spa+e"#i$# of t#e follo%ing $#ar de$larations are valid&

1/ +#ar +#8a9JJ'.


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Example:

int> a9JJre+o""ended to (se be+a(se na"e is +learly separated fro" t#e type

int >a9int a>9

At t#e ti"e of de+laration we +ant spe+ify t#e si0e ot#erwise we will !et +o"pile ti"eerror.

Example:

int> a9JJvalid

int5> a9JJinvalid

Two dimensional array declaration:

Example:

int[][] a;int [][]a;

int a[][]; All are valid.

int[] []a;

int[] a[];

int []a[];

8#ree dimensional arra( de$laration:

Example:

int>>> a9

int >>>a9

int a>>>9

int> >>a9

int> a>>9 7ll are valid9

int> >a>9

int>> >a9

int>> a>9

int >a>>9

int >>a>9

"#i$# of t#e follo%ing de$larations are valid&

1/ int> a1-b19JJa1-b1Bvalid/2/ int> a2>-b29JJa2-b1Bvalid/3/ int> >a3-b39JJa2-b2Bvalid/4/ int> a->b9JJ'.


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Example:

7rra( $onstru$tion: a8new int3>9

'iagram:

Hor every array type +orrespondin! +lasses are available b(t t#ese +lasses are part of,ava lan!(a!e and not available to t#e pro!ra""er level.

7rra( 8(pe $orresponding $lass name

int> I

int>> I

do(ble>

.

.

D

.

.

Rule 1:

At t#e ti"e of array +reation +o"p(lsory we s#o(ld spe+ify t#e si0e ot#erwise we will!et +o"pile ti"e error.

Example:

int> a8new int3>9

int> a8new int>9JJ'. a8new int)>9

Cyste".o(t.printlnBa.len!t#/9JJ)

Rule 3:

If we are ta?in! array si0e wit# ve int val(e t#en we will !et r(nti"e eE+eption sayin!:e!ativeArrayCi0e a8new int3>9JJR.


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byte b81)9

int> a8new intb>9JJBvalid/

s#ort s82)9int> a8new ints>9JJBvalid/

int> a8new int1)l>9JJ'. a8new int1).5>9JJ'..Example:

int> a18new int21474$3647>9Bvalid/

int> a28new int21474$364$>9JJ'.


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"#i$# of t#e follo%ing de$larations are valid&

1/ int> a8new int>JJ'.> a8new int3>4>9Bvalid/3/ int>> a8new int3>>9Bvalid/4/ int>> a8new int>4>9JJ'.Q eEpe+tedBinvalid/5/ int>>> a8new int3>4>5>9Bvalid/6/ int>>> a8new int3>4>>9Bvalid/7/ int>>> a8new int3>>5>9JJ'.Q eEpe+tedBinvalid/

7rra( initialiation @#enever we are +reatin! an array every ele"ent is initiali0ed wit# defa(lt

val(e a(to"ati+ally.

Example 1:

int> a8new int3>9

Cyste".o(t.printlnBa/9JJI[3e25a5

Cyste".o(t.printlnBa)>/9JJ)

'iagram:

/ote:@#enever we are tryin! to print any ob,e+t referen+e internally toCtrin!B/ "et#od will be

eEe+(ted w#i+# is i"ple"ented by defa(lt to ret(rn t#e followin!.

+lassna"e[#eEade+i"alstrin!representationof#as#+ode.

Example 2:


Cyste".o(t.printlnBa)>/9JJI[1&$21f

Cyste".o(t.printlnBa)>)>/9JJ)

'iagram:


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Example 3:

int>> a8new int2>>9


Cyste".o(t.printlnBa)>/9JJn(ll

Cyste".o(t.printlnBa)>)>/9JJR.


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+#ar> +#8QaQ-QeQ-QiQ-QoQ-Q(Q=9Bvalid/

Ctrin!> s8NbalayyaN-Nven?iN-Nna!N-N+#ir(N=9Bvalid/

@e +an eEtend t#is s#ort +(t even for "(lti di"ensional arrays also.Example:

int>> a81)-2)-3)=-4)-5)==9]

'iagram:

Example:

int>>> a81)-2)-3)=-4)-5)==-6)=-7)-$)=-&)-1))-11)===9'iagram:

int>>> a81)-2)-3)=-4)-5)==-6)=-7)-$)=-&)-1))-11)===9

Cyste".o(t.printlnBa)>1>1>/9JJ5)Bvalid/

Cyste".o(t.printlnBa1>)>2>/9JJR.2>2>/9JJ11)Bvalid/

Cyste".o(t.printlnBa2>1>)>/9JJR.


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Example:

int> E8new int3>9

Cyste".o(t.printlnBE.len!t#B//9JJ'.


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int> a8new int>1)-2)-3)-4)=9Bvalid/

Example:

+lass Test

p(bli+ stati+ void "ainBCtrin!> ar!s/

Cyste".o(t.printlnBs("Bnew int>1)-2)-3)-4)=//9JJ1))

=

p(bli+ stati+ int s("Bint> E/

int total8)9

forBint E1E/

total8totalFE19

=

ret(rn total9

=

=

7rra( element assignments:

*ase 1: In t#e +ase of pri"itive array as array ele"ent any type is allowed w#i+# +an be

pro"oted to de+lared type.Example 1:Hor t#e int type arrays t#e allowed array ele"ent types are byte- s#ort- +#ar int.

int> a8new int1)>9

a)>8&79JJBvalid/

a1>8QaQ9JJBvalid/

byte b81)9

a2>8b9JJBvalid/

s#ort s82)9

a3>8s9JJBvalid/

a4>81)l9JJ'. a8new b,e+t1)>9

a)>8new Inte!erB1)/9JJBvalid/

a1>8new b,e+tB/9JJBvalid/

a2>8new Ctrin!BNb#as?arN/9JJBvalid/


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Example 2:

:("ber> n8new :("ber1)>9

n)>8new Inte!erB1)/9JJBvalid/n1>8new Do(bleB1).5/9JJBvalid/

n2>8new Ctrin!BNb#as?arN/9JJ'. r8new R(nnable1)>9

r)>8new T#readB/9

r1>8new Ctrin!BNb#as?arN/9JJ'.


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/ote: In t#e +ase of ob,e+t type arrays +#ild type array +an be assi!n to parent type array

variable.

Example:

Ctrin!> s8NAN-NN=9

b,e+t> o8s9

*ase 2:@#enever we are assi!nin! one array to anot#er array internal ele"ents wont be +opy

,(st referen+e variables will be reassi!ned #en+e si0es are not i"portant b(t types "(st be

"at+#ed.

Example:

int> a81)-2)-3)-4)-5)-6)-7)=9

int> b8$)-&)=9

a8b9JJBvalid/

b8a9JJBvalid/

'iagram:

*ase 3:@#enever we are assi!nin! one array to anot#er array di"ensions "(st be "at+#ed

t#at is in t#e pla+e of one di"ensional array we s#o(ld provide t#e sa"e type only ot#erwise

we will !et +o"pile ti"e error.

Example:

int>> a8new int3>>9

a)>8new int4>5>9JJ'.8new int4>9JJBvalid/

/ote: @#enever we are perfor"in! array assi!n"ents t#e types and di"ensions "(st be

"at+#ed b(t si0es are not i"portant.

Example 1:


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int>> a8new int3>2>9

a)>8new int3>9

a1>8new int4>9

a8new int4>3>9

'iagram:

Total #ow "any ob,e+ts +reatedW

7ns: 11Sow "any ob,e+ts eli!ible for ^' 6

Example 2:

+lass Test


Ctrin!> ar!#8NAN-NN=9

ar!s8ar!#9

Cyste".o(t.printlnBar!s.len!t#/9JJ2

forBint i8)9iZ8ar!s.len!t#9iFF/

Cyste".o(t.printlnBar!si>/9

=

=

=

!utput:

,ava Test E y

R9E:ArrayIndeE(tfo(nds


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R9E:ArrayIndeE(tfo(nds


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If t#e val(e of a variable is varied fro" ob,e+t to ob,e+t s(+# type of variables are +alledinstan+e variables.

Hor every ob,e+t a separate +opy of instan+e variables will be +reated. Instan+e variables will be +reated at t#e ti"e of ob,e+t +reation and destroyed at t#e

ti"e of ob,e+t destr(+tion #en+e t#e s+ope of instan+e variables is eEa+tly sa"e as

s+ope of ob,e+ts.

Instan+e variables will be stored on t#e #eap as t#e part of ob,e+t. Instan+e variables s#o(ld be de+lared wit# in t#e +lass dire+tly b(t o(tside of any

"et#od or blo+? or +onstr(+tor.

Instan+e variables +an be a++essed dire+tly fro" Instan+e area. (t +annot be a++esseddire+tly fro" stati+ area.

(t by (sin! ob,e+t referen+e we +an a++ess instan+e variables fro" stati+ area.Example:

+lass Test

int i81)9


JJCyste".o(t.printlnBi/9JJ'.


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Cyste".o(t.printlnBt.b/9JJfalse

=

= Instan+e variables also ?nown as ob,e+t level variables or attrib(tes.

tati$ varia,les:

If t#e val(e of a variable is not varied fro" ob,e+t to ob,e+t s(+# type of variables is notre+o""ended to de+lare as instan+e variables. @e #ave to de+lare s(+# type of

variables at +lass level by (sin! stati+ "odifier.

In t#e +ase of instan+e variables for every ob,e+t a separate +opy will be +reated b(t int#e +ase of stati+ variables for entire +lass only one +opy will be +reated and s#ared by

every ob,e+t of t#at +lass.

Ctati+ variables will be +rated at t#e ti"e of +lass loadin! and destroyed at t#e ti"e of+lass (nloadin! #en+e t#e s+ope of t#e stati+ variable is eEa+tly sa"e as t#e s+ope of t#e

9$lassfile.

Ctati+ variables will be stored in "et#od area. Ctati+ variables s#o(ld be de+lared wit# int#e +lass dire+tly b(t o(tside of any "et#od or blo+? or +onstr(+tor.

Ctati+ variables +an be a++essed fro" bot# instan+e and stati+ areas dire+tly. @e +an a++ess stati+ variables eit#er by +lass na"e or by ob,e+t referen+e b(t (sa!e of

+lass na"e is re+o""ended.

(t wit#in t#e sa"e +lass it is not reV(ired to (se +lass na"e we +an a++ess dire+tly.1/ Ctart *%.2/ 'reate and start %ain T#read by *%.3/ Lo+ateBfind/ Test.+lass by "ain T#read.4/ Load Test.+lass by "ain T#read.5/


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=

=

Hor t#e stati+ variables it is not reV(ired to perfor" initiali0ation eEpli+itly- *% willalways provide defa(lt val(es.

Example:

+lass Test

stati+ Ctrin! s9


Cyste".o(t.printlnBs/9JJn(ll

==

Example:

+lass Test

int E81)9

stati+ int y82)9


Test t18new TestB/9t1.E8$$$9

t1.y8&&&9

Test t28new TestB/9

Cyste".o(t.printlnBt2.EFNNFt2.y/9JJ1)&&&

=

=

'iagram:

Ctati+ variables also ?nown as +lass level variables or fields.Lo$al varia,les:

Co"e ti"e to "eet te"porary reV(ire"ents of t#e pro!ra""er we +an de+larevariables inside a "et#od or blo+? or +onstr(+tors s(+# type of variables are +alled lo+al

variables or a(to"ati+ variables or te"porary variables or sta+? variables.


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T#e lo+al variables will be +reated as part of t#e blo+? eEe+(tion in w#i+# it is de+laredand destroyed on+e t#at blo+? eEe+(tion +o"pletes. Sen+e t#e s+ope of t#e lo+al

variables is eEa+tly sa"e as s+ope of t#e blo+? in w#i+# we de+lared.Example 1:

+lass Test


int i8)9

forBint ,8)9,Z39,FF/

i8iF,9=

=

=

Example 2:

+lass Test


try

int i8Inte!er.parseIntBNtenN/9

=

+at+#B:(ll\ointer


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Hor t#e lo+al variables *% wont provide any defa(lt val(es +o"p(lsory we s#o(ldperfor" initiali0ation eEpli+itly before (sin! t#at variable.

Example:

Example:

+lass Test


int E9

ifBar!s.len!t#)/

E81)9

=

Cyste".o(t.printlnBE/9JJ'. ar!s/

int E9

ifBar!s.len!t#)/

E81)9

=

else

E82)9

=

Cyste".o(t.printlnBE/9

=


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=

!utput:

,ava Test E1)

,ava Test E y

1)

,ava Test

2)

It is never re+o""ended to perfor" initiali0ation for t#e lo+al variables inside lo!i+alblo+?s be+a(se t#ere is no !(arantee of eEe+(tin! t#at blo+? always at r(nti"e.

It is #i!#ly re+o""ended to perfor" initiali0ation for t#e lo+al variables at t#e ti"e ofde+laration at least wit# defa(lt val(es.

/ote: T#e only appli+able "odifier for lo+al variables is final. If we are (sin! any ot#er

"odifier we will !et +o"pile ti"e error.

Example:

+lass Test


p(bli+ int E81)9private int E81)9

prote+ted int E81)9 *9E: illegal start of expression

stati+ int E81)9

volatile int E81)9

transient int E81)9

final int E81)9JJvalid;

=

=

*on$lusions:1/ Hor t#e stati+ and instan+e variables it is not reV(ired to perfor" initiali0ation eEpli+itly

*% will provide defa(lt val(es. (t for t#e lo+al variables *% wont provide any

defa(lt val(es +o"p(lsory we s#o(ld perfor" initiali0ation eEpli+itly before (sin! t#at

variable.

2/ Hor every ob,e+t a separate +opy of instan+e variable will be +reated w#ereas for entire+lass a sin!le +opy of stati+ variable will be +reated. Hor every T#read a separate +opy of

lo+al variable will be +reated.


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3/ Instan+e and stati+ variables +an be a++essed by "(ltiple T#reads si"(ltaneo(sly and#en+e t#ese are not T#read safe b(t lo+al variables +an be a++essed by only one T#read

at a ti"e and #en+e lo+al variables are T#read safe../ initialied arra(s

Example:

+lass Test

int> a9


Test t18new TestB/9

Cyste".o(t.printlnBt1.a/9JJn(llCyste".o(t.printlnBt1.a)>/9JJR./9JJR.9

Cyste".o(t.printlnBob,.a/9JJI[3e25a5

Cyste".o(t.printlnBob,.a)>/9JJ)

tati$ level:

Example 1:

stati+ int> a9

Cyste".o(t.printlnBa/9JJn(ll

Cyste".o(t.printlnBa)>/9JJR.9


Cyste".o(t.printlnBa)>/9JJ)

Lo$al level:

Example 1:

int> a9

Cyste".o(t.printlnBa/9 *9E: varia,le a mig#t not #ave ,een initialied

Cyste".o(t.printlnBa)>/9


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Example 2:

int> a8new int3>9

Cyste".o(t.printlnBa/9JJI[3e25a5Cyste".o(t.printlnBa)>/9JJ)

n+e we +reated an array every ele"ent is always initiali0ed wit# defa(lt val(esirrespe+tive of w#et#er it is stati+ or instan+e or lo+al array.

-ar< arg met#ods varia,le no of argument met#ods; 195;

;ntil 1.4v we +ant de+lared a "et#od wit# variable no. f ar!("ents. If t#ere is a+#an!e in no of ar!("ents +o"p(lsory we #ave to define a new "et#od. T#is approa+#

in+reases len!t# of t#e +ode and red(+es readability. (t fro" 1.5 version onwards we

+an de+lare a "et#od wit# variable no. f ar!("ents s(+# type of "et#ods are +alled

varar! "et#ods. @e +an de+lare a varar! "et#od as follows.

@e +an +all or invo?e t#is "et#od by passin! any no. f int val(es in+l(din! 0eron("ber.

Example:

+lass Test

p(bli+ stati+ void "et#odneBint... E/

Cyste".o(t.printlnBNvarar! "et#odN/9

=


"et#odneB/9

"et#odneB1)/9

"et#odneB1)-2)-3)/9

=

=

!utput:

varar! "et#od

varar! "et#od

varar! "et#od

Internally varar! para"eter i"ple"ented by (sin! sin!le di"ensional array #en+ewit#in t#e varar! "et#od we +an different ar!("ents by (sin! indeE.

Example:


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+lass Test

p(bli+ stati+ void s("Bint... E/

int total8)9

forBint i8)9iZE.len!t#9iFF/

total8totalFEi>9

=

Cyste".o(t.printlnBNT#e s(" NFtotal/9

=


s("B/9

s("B1)/9

s("B1)-2)/9

s("B1)-2)-3)-4)/9

=

=

!utput:

T#e s(" )T#e s(" 1)

T#e s(" 3)

T#e s(" 1))

*ase 1:

"#i$# of t#e follo%ing var


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"et#odneBint... a-int b/Binvalid/

*ase 4:@e +an ta?e only one varar! para"eter inside varar! "et#od

Example:"et#odneBint... a-int... b/Binvalid/

*ase 5:

+lass Test

p(bli+ stati+ void "et#odneBint i/

Cyste".o(t.printlnBN!eneral "et#odN/9

=

p(bli+ stati+ void "et#odneBint... i/


=


"et#odneB/9JJvarar! "et#od

"et#odneB1)-2)/9JJvarar! "et#od

"et#odneB1)/9JJ!eneral "et#od

==

In !eneral varar! "et#od will !et least priority t#at is if no ot#er "et#od "at+#ed t#enonly varar! "et#od will !et t#e +#an+e t#is is eEa+tly sa"e as defa(lt +ase inside a

swit+#.

*ase 6:Hor t#e varar! "et#ods we +an provide t#e +orrespondin! type array as ar!("ent.

Example:

+lass Test


=


"et#odneBnew int>1)-2)-3)=/9JJvarar! "et#od

=


35/459

35

=

*ase :

+lass Test

p(bli+ void "et#odneBint> i/=

p(bli+ void "et#odneBint... i/=

=

!utput:

'o"pile ti"e error.

'annot de+lare bot# "et#odneBint.../ and "et#odneBint>/ in Test

ingle 'imensional 7rra( -s -ar/9

=

=


int> l81)-2)-3)=9


36/459

36

int> "84)-5)=9

"et#odneBl-"/9

=

=

!utput:

1)

4)

7nal(sis:

=ain =et#od

@#et#er t#e +lass +ontains "ainB/ "et#od or not and w#et#er it is properly de+lared ornot t#ese +#e+?in!s are not responsibilities of t#e +o"piler- at r(nti"e *% is

responsible for t#is. If ,v" (nable to find t#e reV(ired "ainB/ "et#od t#en we will !et

r(nti"e eE+eption sayin! :oC(+#%et#od


37/459

37

1/ T#e order of "odifiers is not i"portant t#at is instead of p(bli+ stati+ we +an ta?e stati+p(bli+.

2/ @e +an de+lare strin!> in any a++eptable for"1/ Ctrin!> ar!s2/ Ctrin! >ar!s3/ Ctrin! ar!s>

3/ Instead of ar!s we +an (se any valid ,ava identifier.4/ @e +an repla+e strin!> wit# varar! para"eter.

Example:

"ainBCtrin!... ar!s/

5/ "ainB/ "et#od +an be de+lared wit# t#e followin! "odifiers. final- syn+#roni0ed- stri+tfp.

"#i$# of t#e follo%ing main; met#od de$larations are valid&

1/ p(bli+ stati+ void "ainBCtrin! ar!s/=Binvalid/2/ p(bli+ syn+#roni0ed final stri+tfp void "ainBCtrin!> ar!s/= Binvalid/3/ p(bli+ stati+ void %ainBCtrin!... ar!s/= Binvalid/4/ p(bli+ stati+ int "ainBCtrin!> ar!s/=JJint ret(rn type we +anQt ta?eJJBinvalid/5/ p(bli+ stati+ syn+#roni0ed final stri+tfp void "ainBCtrin!... ar!s/=Bvalid/

In %#i$# of t#e a,ove $ases %e %ill get $ompile time error&

:o +ase- in all t#e +ases we will !et r(nti"e eE+eption. verloadin! of t#e "ainB/ "et#od is possible b(t *% always +alls strin!> ar!("ent

"ainB/ "et#od only.

Example:

+lass Test


Cyste".o(t.printlnBNCtrin!> array "ain "et#odN/9 overloaded met#ods

=

p(bli+ stati+ void "ainBint> ar!s/

Cyste".o(t.printlnBNint> array "ain "et#odN/9

=

=

!utput:

Ctrin!> array "ain "et#od

T#e ot#er overloaded "et#od we #ave to +all eEpli+itly t#en only it will be eEe+(ted.


38/459

3$

In#eritan+e +on+ept is appli+able for stati+ "et#ods in+l(din! "ainB/ "et#od #en+ew#ile eEe+(tin! +#ild +lass if t#e +#ild +lass doesnt +ontain "ainB/ "et#od t#en t#e

parent +lass "ainB/ "et#od will be eEe+(ted.Example 1:

+lass \arent


Cyste".o(t.printlnBNparent "ainN/9 arent9java

=

=

+lass '#ild eEtends \arent=

7nal(sis:

Example 2:

+lass \arent


Cyste".o(t.printlnBNparent "ainN/9

=

=+lass '#ild eEtends \arent arent9java


Cyste".o(t.printlnBN'#ild "ainN/9

=

=

7nal(sis:


39/459

3&

It see"s to be overridin! +on+ept is appli+able for stati+ "et#ods b(t it is not overridin!it is "et#od #idin!.

*ommand line arguments:

T#e ar!("ents w#i+# are passin! fro" +o""and pro"pt are +alled +o""and linear!("ents. T#e "ain ob,e+tive of +o""and line ar!("ents are we +an +(sto"i0e t#e

be#avior of t#e "ainB/ "et#od.

Example 1:

+lass Test


forBint i8)9iZ8ar!s.len!t#9iFF/

Cyste".o(t.printlnBar!si>/9

=

=

=

!utput:

,ava Test E y 0

ArrayIndeE(tfo(nds?@operator a+ts as strin! +on+atenation b(t not arit#"eti+ addition.

Example:

+lass Test


40/459

4)


Cyste".o(t.printlnBar!s)>Far!s1>/9

=

=

!utput:

/9

=

=

!utput:


41/459

41

;s(ally +lass na"es are no(ns. C#o(ld starts wit# (pper+ase letter and if it +ontains "(ltiple words every inner word

s#o(ld starts wit# (pper +ase letter.Example:

*oding standards for interfa$es:

;s(ally interfa+e na"es are ad,e+tives. C#o(ld starts wit# (pper +ase letter and if it +ontains "(ltiple words every inner word

s#o(ld starts wit# (pper +ase letter.

Example:

1/ Ceriali0able2; R(nnable adje$tives3/ 'loneable

*oding standards for met#ods:

;s(ally "et#od na"es are eit#er verbs or verb no(n +o"bination. C#o(ld starts wit# lower+ase +#ara+ter and if it +ontains "(ltiple words every inner

word s#o(ld starts wit# (pper +ase letter.

Example:

*oding standards for varia,les:

;s(ally variable na"es are no(ns. C#o(ld starts wit# lower+ase alp#abet sy"bol and if it +ontains "(ltiple words every

inner word s#o(ld starts wit# (pper +ase +#ara+ter.

Example:

len!t#

na"e

salary nouns

a!e

"obile:("ber

*oding standards for $onstants:

;s(ally +onstants are no(ns. C#o(ld +ontain only (pper+ase +#ara+ters and if it +ontains "(ltiple words t#en t#ese

words are separated wit# (nders+ore sy"bol.


42/459

42

;s(ally we +an de+lare +onstants by (sin! pu,li$ stati$ final modifiers9Example:

%APAL;< nouns%I:AL;/

Cyste".o(t.printlnBNA +lass "ain "et#od is eEe+(tedN/9

=

=

+lass

p(bli+ stati+ void "ainBCtrin! ar!s>/

Cyste".o(t.printlnBN +lass "ain "et#od is eEe+(tedN/9

=

=

+lass '


Cyste".o(t.printlnBN' +lass "ain "et#od is eEe+(tedN/9=

=

+lass D

=

!utput:


46/459

46

DY*ava,ava A

A +lass "ain "et#od is eEe+(ted

DY*ava,ava

+lass "ain "et#od is eEe+(ted

DY*ava,ava '

' +lass "ain "et#od is eEe+(ted

DY*ava,ava D

/

ArrayList l8new ArrayListB/9

=

=

!utput:

'o"pile ti"e error.

DY*ava,ava+ Test.,ava

Test.,ava3 +annot find sy"bol

sy"bol +lass ArrayList

lo+ation +lass Test


Test.,ava3 +annot find sy"bol

sy"bol +lass ArrayList

lo+ation +lass Test


47/459

47


@e +an resolve t#is proble" by (sin! f(lly V(alified na"e K,ava.(til.ArrayList l8new,ava.(til.ArrayListB/9. (t proble" wit# (sin! f(lly V(alified na"e every ti"e is itin+reases len!t# of t#e +ode and red(+es readability.

@e +an resolve t#is proble" by (sin! i"port state"ents.Example:

i"port ,ava.(til.ArrayList9

+lass Test



=

=!utput:


Sen+e w#enever we are (sin! i"port state"ent it is not reV(ire to (se f(lly V(alifiedna"es we +an (se s#ort na"es dire+tly. T#is approa+# de+reases len!t# of t#e +ode and

i"proves readability.

*ase 1: 8(pes of Import tatements:

T#ere are 2 types of i"port state"ents.1/


48/459

4$

+lass %yArrayList eEtends ,ava.(til.ArrayList

= T#e +ode +o"piles fine even t#o(!# we are not (sin! i"port state"ents be+a(se we

(sed f(lly V(alified na"e.

@#enever we are (sin! f(lly V(alified na"e it is not reV(ired to (se i"port state"ent.Ci"ilarly w#enever we are (sin! i"port state"ents it is not reV(ire to (se f(lly V(alified

na"e.

*ase4:

Example:

i"port ,ava.(til.U9

i"port ,ava.sVl.U9+lass Test


Date d8new DateB/9

==

!utput:

'o"pile ti"e error.

DY*ava,ava+ Test.,avaTest.,ava7 referen+e to Date is a"bi!(o(s- bot# +lass ,ava.sVl.Date in ,ava.sVl and +lass

,ava.(til.Date in ,ava.(til "at+#

Date d8new DateB/9

/ote:


49/459

4&

Date d8new DateB/9

==

T#e +ode +o"piles fine and in t#is +ase (til pa+?a!e Date will be +onsidered.*ase6:

@#enever we are i"portin! a pa+?a!e all +lasses and interfa+es present in t#at pa+?a!eare by defa(lt available b(t not s(b pa+?a!e +lasses.

Example:

8o use pattern $lass in our program dire$tl( %#i$# import statement is reAuired&

*ase:

In any ,ava pro!ra" t#e followin! 2 pa+?a!es are not reV(ire to i"port be+a(se t#eseare available by defa(lt to every ,ava pro!ra".

1. ,ava.lan! pa+?a!e2. defa(lt pa+?a!eB+(rrent wor?in! dire+tory/

*aseB:

KI"port state"ent is totally +o"pile ti"e +on+ept if "ore no of i"ports are t#ere t#en"ore will be t#e +o"pile ti"e b(t t#ere is Kno +#an!e in eEe+(tion ti"e.

'ifferen$e ,et%een * language Cin$lude and java language import9

In t#e +ase of ' lan!(a!e in+l(de all t#e #eader files will be loaded at t#e ti"e ofin+l(de state"ent #en+e it follows stati+ loadin!.

(t in ,ava i"port state"ent no K.+lass will be loaded at t#e ti"e of i"port state"entsin t#e neEt lines of t#e +ode w#enever we are (sin! a parti+(lar +lass t#en only

+orrespondin! K.+lass file will be loaded. Sen+e it follows Kdyna"i+ loadin! or Kload

on Mde"and or Kloadonfly.

tati$ import:

T#is +on+ept introd(+ed in 1.5 versions. A++ordin! to s(n stati+ i"port i"provesreadability of t#e +ode b(t a++ordin! to worldwide pro!ra""in! eEports Bli?e (s/ stati+


50/459

5)

i"ports +reates +onf(sion and red(+es readability of t#e +ode. Sen+e if t#ere is no

spe+ifi+ reV(ire"ent never re+o""ended to (se a stati+ i"port.

195 versions ne% features1/ Hor


51/459

51

==

!utput:

DY*ava,ava+ Test.,avaDY*ava,ava Test

2.)

2)

).43)2$53$47363$&1

Explain a,out (stem9out9println statement&

Example 1 and example 2:

Example 3:

i"port stati+ ,ava.lan!.Cyste".o(t9

+lass Test


o(t.printlnBN#elloN/9

o(t.printlnBN#iN/9==

!utput:


DY*ava,ava Test

#ello

#i

Example 4:

i"port stati+ ,ava.lan!.Inte!er.U9


52/459

52

i"port stati+ ,ava.lan!.yte.U9

+lass Test


Cyste".o(t.printlnB%APAL;


53/459

53

'iagram:

;sa!e of stati+ i"port red(+es readability and +reates +onf(sion #en+e if t#ere is nospe+ifi+ reV(ire"ent never re+o""ended to (se stati+ i"port.

"#at is t#e differen$e ,et%een general import and stati$ import&

@e +an (se nor"al i"ports to i"port +lasses and interfa+es of a pa+?a!e. w#enever weare (sin! nor"al i"port we +an a++ess +lass and interfa+es dire+tly by t#eir s#ort na"eit is not reV(ire to (se f(lly V(alified na"es.

@e +an (se stati+ i"port to i"port stati+ "e"bers of a parti+(lar +lass. w#enever weare (sin! stati+ i"port it is not reV(ire to (se +lass na"e we +an a++ess stati+ "e"bers

dire+tly.

a$+age statement:

It is an en+aps(lation "e+#anis" to !ro(p related +lasses and interfa+es into a sin!le"od(le.

8#e main o,je$tives of pa$+ages are:

To resolve na"e +onfe+ts. To i"prove "od(larity of t#e appli+ation. To provide se+(rity.

T#ere is one (niversally a++epted na"in! +onversion for pa+?a!es t#at is to (se internetdo"ain na"e in reverse.

Example:

o% to $ompile pa$+age program:

Example:

pa+?a!e +o".d(r!a,obs.it,obs9

+lass Syd*obs


Cyste".o(t.printlnBNpa+?a!e de"oN/9


54/459

54

=

=

*ava+ Syd*obs.,ava !enerated +lass file will be pla+ed in +(rrent wor?in! dire+tory.'iagram:

*ava+ Md . Syd*obs.,ava d "eans destination to pla+e !enerated +lass files K. "eans +(rrent wor?in! dire+tory. ^enerated +lass file will be pla+ed into +orrespondin! pa+?a!e str(+t(re.

'iagram:

If t#e spe+ified pa+?a!e str(+t(re is not already available t#en t#is +o""and itself will+reate t#e reV(ired pa+?a!e str(+t(re.

As t#e destination we +an (se any valid dire+tory.If t#e spe+ified destination is not available t#en we will !et +o"pile ti"e error.

Example:

DY*ava,ava+ d + Syd*obs.,ava

'iagram:

If t#e spe+ified destination is not available t#en we will !et +o"pile ti"e error.Example:

DY*ava,ava+ d 0 Syd*obs.,ava

If is not available t#en we will !et +o"pile ti"e error.o% to exe$ute pa$+age program:

DY*ava,ava +o".d(r!a,obs.it,obs.Syd*obs

At t#e ti"e of eEe+(tion +o"p(lsory we s#o(ld provide f(lly V(alified na"e.*on$lusion 1:


55/459

55

In any ,ava pro!ra" t#ere s#o(ld be at "ost one pa+?a!e state"ent t#at is if we areta?in! "ore t#an one pa+?a!e state"ent we will !et +o"pile ti"e error.

Example:pa+?a!e pa+?19

pa+?a!e pa+?29

+lass A

=

!utput:

'o"pile ti"e error.

DY*ava,ava+ A.,ava

A.,ava2 +lass- interfa+e- or en(" eEpe+tedpa+?a!e pa+?29

*on$lusion 2:

In any ,ava pro!ra" t#e 1stnon +e"ent state"ent s#o(ld be pa+?a!e state"ent if it isavailable> ot#erwise we will !et +o"pile ti"e error.

Example:

i"port ,ava.(til.U9

pa+?a!e pa+?19

+lass A

=

!utput:

'o"pile ti"e error.

DY*ava,ava+ A.,ava

A.,ava2 +lass- interfa+e- or en(" eEpe+ted

pa+?a!e pa+?19

0ava sour$e file stru$ture:

All t#e followin! are valid ,ava pro!ra"s.

/ote:An e"pty so(r+e file is a valid ,ava pro!ra".

*lass =odifiers


56/459

56

@#enever we are writin! o(r own +lasses +o"p(lsory we #ave to provide so"einfor"ation abo(t o(r +lass to t#e ,v". Li?e

1/ etter t#is +lass +an be a++essible fro" anyw#ere or not.2/ etter +#ild +lass +reation is possible or not.3/ @#et#er ob,e+t +reation is possible or not et+.

@e +an spe+ify t#is infor"ation by (sin! t#e +orrespondin! "odifiers. T#e only appli+able "odifiers for 8op Level+lasses are

1/ \(bli+2/ Defa(lt3/ Hinal4/ Abstra+t5/ Ctri+tfp

If we are (sin! any ot#er "odifier we will !et +o"pile ti"e error.Example:

private +lass Test


int i8)9

forBint ,8)9,Z39,FF/

i8iF,9=

Cyste".o(t.printlnBi/9

==

!.8.8:

'o"pile ti"e error.


Test.,ava1 "odifier private not allowed #ere

private +lass Test (t Hor t#e inner +lasses t#e followin! "odifiers are allowed.

'iagram:

"#at is t#e differen$e ,et%een a$$ess spe$ifier and a$$ess modifier& In old lan!(a!es X' Bor/ X'FF pu,li$- private- prote$ted- default are +onsidered as

a++ess spe+ifiers and all t#e re"ainin! are +onsidered as a++ess "odifiers.


57/459

57

(t in ,ava t#ere is no s(+# type of division all are +onsidered as a++ess "odifiers.u,li$ *lasses

If a +lass de+lared as p(bli+ t#en we +an a++ess t#at +lass fro" anyw#ere.ED7=LE:

rogram1:

pa+?a!e pa+?19

p(bli+ +lass Test

p(bli+ void "et#odneB/

Cyste".o(t.printlnBNtest +lass "et#odone is eEe+(tedN/9

==

*ompile t#e a,ove program:DY*ava,ava+ d . Test.,ava

rogram2:

pa+?a!e pa+?29

i"port pa+?1.Test9

+lass Test1


Test t8new TestB/9

t."et#odneB/9==

!.8.8:

DY*ava,ava+ d . Test1.,ava

DY*ava,ava pa+?2.Test1

Test +lass "et#odone is eEe+(ted.

If +lass Test is not p(bli+ t#en w#ile +o"pilin! Test1 +lass we will !et +o"pile ti"e errorsayin! pa$+198est is not pu,li$ in pa$+1 $annot ,e a$$essed from outside pa$+age.

'efault *lasses:

If a +lass de+lared as t#e defaultt#en we +an a++ess t#at +lass only %it#in t#e $urrentpa$+age#en+e defa(lt a++ess is also ?nown as Kpa$+age level a$$ess.

Example:

rogram 1:

pa+?a!e pa+?19

+lass Test


Cyste".o(t.printlnBNtest +lass "et#odone is eEe+(tedN/9


58/459

5$

==

rogram 2:

pa+?a!e pa+?19i"port pa+?1.Test9

+lass Test1


Test t8new TestB/9

t."et#odneB/9

==

!.8.8:

DY*ava,ava+ d . Test.,avaDY*ava,ava+ d . Test1.,ava

DY*ava,ava pa+?1.Test1

Test +lass "et#odone is eEe+(ted

Final =odifier

Hinal is t#e "odifier appli+able for +lasses- "et#ods and variables.Final =et#ods:

@#atever t#e "et#ods parent #as by defa(lt available to t#e +#ild. If t#e +#ild is not allowed to override any "et#od- t#at "et#od we #ave to de+lare wit#

final in parent +lass. T#at is final "et#ods +annot overridden.Example:

rogram 1:

+lass \arent

p(bli+ void propertyB/

Cyste".o(t.printlnBN+as#F!oldFlandN/9

=

p(bli+ final void "arria!eB/

Cyste".o(t.printlnBNs(bbala?s#"iN/9==

rogram 2:

+lass +#ild eEtends \arent

p(bli+ void "arria!eB/

Cyste".o(t.printlnBNT#a"annaN/9

==

!.8.8:


59/459

5&

'o"pile ti"e error.

DY*ava,ava+ \arent.,ava

DY*ava,ava+ +#ild.,ava$#ild9java:3: marriage; in $#ild $annot override marriage; in arent overridden met#od is

final

pu,li$ void marriage;

Final *lass:

If a +lass de+lared as t#e final t#en we +annt +reates t#e +#ild +lass t#at is in#eritan+e+on+ept is not appli+able for final +lasses.

ED7=LE:

rogram 1:

final +lass \arent

=

rogram 2:


=

!.8.8:

'o"pile ti"e error.

DY*ava,ava+ \arent.,avaDY*ava,ava+ +#ild.,ava

$#ild9java:1:$annot in#erit from final arent

+lass +#ild eEtends \arent :ote


60/459

6)

7,stra$t =odifier:

Abstra+t is t#e "odifier appli+able only for "et#ods and +lasses b(t not for variables.7,stra$t =et#ods:


61/459

61

All t#e 6 +o"binations are ille!al.7,stra$t $lass:

Hor any ,ava +lass if we are not allow to +reate an ob,e+t s(+# type of +lass we #ave tode+lare wit# abstra+t "odifier t#at is for abstra+t +lass instantiation is not possible.

Example:

abstra+t +lass Test


Test t8new TestB/9

==

!utput:

'o"pile ti"e error.DY*ava,ava+ Test.,ava

Test.,ava4 Test is abstra+t9 +annot be instantiated

Test t8new TestB/9

"#at is t#e differen$e ,et%een a,stra$t $lass and a,stra$t met#od&

If a +lass +ontain at least on abstra+t "et#od t#en +o"p(lsory t#e +orrespondin! +lasss#o(ld be de+lare wit# abstra+t "odifier. e+a(se i"ple"entation is not +o"plete and

#en+e we +ant +reate ob,e+t of t#at +lass.


62/459

62

'o"pile ti"e error.


\arent.,ava3 "issin! "et#od body- or de+lare abstra+tp(bli+ void "et#odneB/9

Example2:

+lass \arent

p(bli+ abstra+t void "et#odneB/=

=

!utput:

'o"pile ti"e error.

\arent.,ava3 abstra+t "et#ods +annot #ave a bodyp(bli+ abstra+t void "et#odneB/=

Example3:

+lass \arent

p(bli+ abstra+t void "et#odneB/9

=

!utput:

'o"pile ti"e error.

DY*ava,ava+ \arent.,ava\arent.,ava1 \arent is not abstra+t and does not override abstra+t "et#od "et#odneB/ in

\arent

+lass \arent

If a +lass eEtends any abstra+t +lass t#en +o"p(lsory we s#o(ld provide i"ple"entationfor every abstra+t "et#od of t#e parent +lass ot#erwise we #ave to de+lare +#ild +lass as

abstra+t.

Example:

abstra+t +lass \arent

p(bli+ abstra+t void "et#odneB/9

p(bli+ abstra+t void "et#odTwoB/9

=


p(bli+ void "et#odneB/=

=

!utput:


63/459

63

'o"pile ti"e error.


\arent.,ava6 +#ild is not abstra+t and does not override abstra+t "et#od "et#odTwoB/ in\arent


If we de+lare +lass +#ild as abstra+t t#en t#e +ode +o"piles fine b(t +#ild of +#ild isresponsible to provide i"ple"entation for "et#odTwoB/.

"#at is t#e differen$e ,et%een final and a,stra$t&

Hor abstra+t "et#ods +o"p(lsory we s#o(ld override in t#e +#ild +lass to providei"ple"entation. @#ereas for final "et#ods we +ant override #en+e abstra+t final

+o"bination is ille!al for "et#ods.

Hor abstra+t +lasses we s#o(ld +o"p(lsory +reate +#ild +lass to provide i"ple"entationw#ereas for final +lass we +ant +reate +#ild +lass. Sen+e final abstra+t +o"bination is

ille!al for +lasses.

Hinal +lass +annot +ontain abstra+t "et#ods w#ereas abstra+t +lass +an +ontain final"et#od.

Example:

/ote:

;sa!e of abstra+t "et#ods- abstra+t +lasses and interfa+es is always !ood pro!ra""in!pra+ti+e.

tri$tfp:

stri+tfp is t#e "odifier appli+able for "et#ods and +lasses b(t not for variables.

Ctri+tfp "odifier introd(+ed in 1.2 versions. If a "et#od de+lare as t#e Ctri+tfp t#en all t#e floatin! point +al+(lations in t#at "et#od

#as to follow I


64/459

64

If a +lass de+lares as t#e Ctri+tfp t#en every +on+rete "et#odBw#i+# #as body/ of t#at+lass #as to follow I


65/459

65

DY*ava,ava+ d . .,ava

.,ava2 pa+?1.A is not p(bli+ in pa+?19 +annot be a++essed fro" o(tside pa+?a!e

i"port pa+?1.A9 In t#e above pro!ra" even t#o(!# "et#odneB/ "et#od is p(bli+ we +ant a++ess fro"

+lass be+a(se t#e +orrespondin! +lass A is not p(bli+ t#at is bot# +lasses and "et#ods

are p(bli+ t#en only we +an a++ess.

'efault mem,er:

If a "e"ber de+lared as t#e defa(lt t#en we +an a++ess t#at "e"ber only wit#in t#e+(rrent pa+?a!e #en+e defa(lt "e"ber is also ?nown as pa+?a!e level a++ess.

Example 1:

rogram 1:

pa+?a!e pa+?19+lass A

void "et#odneB/

Cyste".o(t.printlnBN"et#odne is eEe+(tedN/9

==

rogram 2:

pa+?a!e pa+?19

i"port pa+?1.A9

+lass


A a8new AB/9

a."et#odneB/9

==

!utput:

DY*ava,ava+ d . A.,ava


DY*ava,ava pa+?1."et#odne is eEe+(ted

Example 2:

rogram 1:

pa+?a!e pa+?19

+lass A

void "et#odneB/



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66

==

rogram 2:

pa+?a!e pa+?29i"port pa+?1.A9

+lass


A a8new AB/9

a."et#odneB/9

==

!utput:

'o"pile ti"e error.DY*ava,ava+ d . A.,ava


.,ava2 pa+?1.A is not p(bli+ in pa+?19 +annot be a++essed fro" o(tside pa+?a!e

i"port pa+?1.A9

rivate mem,ers:

If a "e"ber de+lared as t#e private t#en we +an a++ess t#at "e"ber only wit# in t#e+(rrent +lass.

\rivate "et#ods are not visible in +#ild +lasses w#ere as abstra+t "et#ods s#o(ld bevisible in +#ild +lasses to provide i"ple"entation #en+e private- a,stra$t +o"bination isille!al for "et#ods.

rote$ted mem,ers:

If a "e"ber de+lared as t#e prote+ted t#en we +an a++ess t#at "e"ber wit#in t#e+(rrent pa+?a!e anyw#ere b(t o(tside pa+?a!e only in +#ild +lasses.

\rote+ted8defa(ltF?ids. @e +an a++ess prote+ted "e"bers wit#in t#e +(rrent pa+?a!e anyw#ere eit#er by +#ild

referen+e or by parent referen+e b(t fro" o(tside pa+?a!e we +an a++ess prote+ted

"e"bers only in +#ild +lasses and s#o(ld be by +#ild referen+e only t#at is we +ant (se

parent referen+e to +all prote+ted "e"bers fro" o(tside lan!(a!e.Example:

rogram 1:

pa+?a!e pa+?19

p(bli+ +lass A

prote+ted void "et#odneB/


==


67/459

67

rogram 2:

pa+?a!e pa+?19

+lass eEtends A


A a8new AB/9

a."et#odneB/9

b8new B/9

b."et#odneB/9

A a18new B/9

a1."et#odneB/9

==!utput:

DY*ava,ava+ d . A.,ava


DY*ava,ava pa+?1.

"et#odne is eEe+(ted



Example 2:

*ompression of privateH defaultH prote$ted and pu,li$:

visi,ilit( private default prote$ted pu,li$

1;"it# in t#e

same $lass

2;From $#ild

$lass of same

pa$+age

3;From non/

Test t8new TestB/9

Cyste".o(t.printlnBt.i/9

==

!utput:


DY*ava,ava Test


69/459

6&

)

If t#e instan+e variable de+lared as t#e final +o"p(lsory we s#o(ld perfor" initiali0ationw#et#er we are (sin! or not ot#erwise we will !et +o"pile ti"e error.

Example:

rogram 1:

+lass Test

int i9

=

!utput:


DY*avarogram 2:

+lass Test

final int i9

=

!utput:

'o"pile ti"e error.


Test.,ava1 variable i "i!#t not #ave been initiali0ed+lass Test

Rule:

Hor t#e final instan+e variables we s#o(ld perfor" initiali0ation before +onstr(+tor+o"pletion. T#at is t#e followin! are vario(s possible pla+es for t#is.

1; 7t t#e time of de$laration:Example:

+lass Test

final int i81)9=

!utput:


DY*ava

2; Inside instan$e ,lo$+:Example:

+lass Test


70/459

7)

final int i9

i81)9==

!utput:


DY*ava

3; Inside $onstru$tor:Example:

+lass Test

final int i9TestB/

i81)9

==

!utput:


DY*ava

If we are perfor"in! initiali0ation anyw#ere else we will !et +o"pile ti"e error.Example:+lass Test

final int i9


i81)9

==

!utput:

'o"pile ti"e error.

DY*ava,ava+ Test.,avaTest.,ava5 +annot assi!n a val(e to final variable i

i81)9

Final stati$ varia,les:

If t#e val(e of a variable is not varied fro" ob,e+t to ob,e+t s(+# type of variables is notre+o""ended to de+lare as t#e instan+e variables. "e #ave to de$lare t#ose varia,les

at $lass level ,( using stati$ modifier9

Hor t#e stati+ variables it is not reV(ired to perfor" initiali0ation eEpli+itly ,v" willalways provide defa(lt val(es.


71/459

71

Example:

+lass Test

stati+ int i9


Cyste".o(t.printlnBNval(e of i is NFi/9

==

!utput:


DY*ava,ava Test

al(e of i is )

If t#e stati+ variable de+lare as final t#en +o"p(lsory we s#o(ld perfor" initiali0ationeEpli+itly w#et#er we are (sin! or not ot#erwise we will !et +o"pile ti"e error.

Example:

Rule:

Hor t#e final stati+ variables we s#o(ld perfor" initiali0ation before +lass loadin!+o"pletion ot#erwise we will !et +o"pile ti"e error. T#at is t#e followin! are possible

pla+es.

1; 7t t#e time of de$laration:Example:

+lass Test

final stati+ int i81)9

=

!utput:


DY*ava

2; Inside stati$ ,lo$+:Example:

+lass Test

final stati+ int i9


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72

stati+

i81)9==

!utput:

'o"pile s(++essf(lly.

If we are perfor"in! initiali0ation anyw#ere else we will !et +o"pile ti"e error.Example:

+lass Test

final stati+ int i9

p(bli+ stati+ void "ainBCtrin! ar!s>/i81)9

==

!utput:

'o"pile ti"e error.


Test.,ava5 +annot assi!n a val(e to final variable i

i81)9

Final lo$al varia,les: To "eet te"porary reV(ire"ent of t#e pro!ra""er so"eti"e we +an de+lare t#e

variable inside a "et#od or blo+? or +onstr(+tor s(+# type of variables are +alled lo+al

variables.

Hor t#e lo+al variables ,v" wont provide any defa(lt val(e +o"p(lsory we s#o(ldperfor" initiali0ation eEpli+itly before (sin! t#at variable.

Example:

+lass Test

p(bli+ stati+ void "ainBCtrin! ar!s>/int i9

Cyste".o(t.printlnBN#elloN/9

==

!utput:


DY*ava,ava Test

Sello

Example:


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73

+lass Test

p(bli+ stati+ void "ainBCtrin! ar!s>/int i9


==

!utput:

'o"pile ti"e error.


Test.,ava5 variable i "i!#t not #ave been initiali0ed


/

final int i9


==

!utput:DY*ava,ava+ Test.,ava

DY*ava,ava Test

#ello

/ote: 8#e onl( appli$a,le modifier for lo$al varia,les is final if %e are using an( ot#er

modifier %e %ill get $ompile time error9

Example:

!utput:

'o"pile ti"e error.


74/459

74


Test.,ava5 ille!al start of eEpression

private int E81)9Formal parameters:

T#e for"al para"eters of a "et#od are si"ply a++ess lo+al variables of t#at "et#od#en+e it is possible to de+lare for"al para"eters as final.

If we de+lare for"al para"eters as final t#en we +ant +#an!e its val(e wit#in t#e"et#od.

Example:

tati$ modifier: Ctati+ is t#e "odifier appli+able for "et#ods- variables and blo+?s. @e +ant de+lare a +lass wit# stati+ ,ut inner $lasses$an ,e de$laring as t#e stati$. In t#e +ase of instan+e variables for every ob,e+t a separate +opy will be +reated b(t in

t#e +ase of stati+ variables a sin!le +opy will be +reated at +lass level and s#ared by all

ob,e+ts of t#at +lass.

Example:

!utput:


75/459

75


DY*ava,ava Test

$$$.....2) Instan+e variables +an be a++essed only fro" instan$e area dire$tl( and %e $ant a$$ess

from stati$ area dire$tl(.

(t stati+ variables +an be a++essed fro" ,ot# instan$e and stati$ areas dire$tl(.1/ Int E81)92/ Ctati+ int E81)93/ \(bli+ void "et#odneB/


=

4/ \(bli+ stati+ void "et#odneB/Cyste".o(t.printlnBE/9

=

"#i$# are t#e follo%ing de$larations are allo% %it#in t#e same $lass simultaneousl(&

a; 1 and 3Example:

+lass Test

int E81)9



==

!utput:


,; 1 and 4Example:

+lass Test

int E81)9

p(bli+ stati+ void "et#odneB/


==

!utput:

'o"pile ti"e error.


Test.,ava5 nonstati+ variable E +annot be referen+ed fro" a stati+ +onteEt


$; 2 and 3Example:

+lass Test


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76

stati+ int E81)9



==

!utput:


d; 2 and 4Example:

+lass Test

stati+ int E81)9p(bli+ stati+ void "et#odneB/


==

!utput:


e; 1 and 2Example:

+lass Test

int E81)9stati+ int E81)9

=

!utput:

'o"pile ti"e error.


Test.,ava4 E is already defined in Test

stati+ int E81)9

f; 3 and 4Example:

+lass Testp(bli+ void "et#odneB/


=



==

!utput:

'o"pile ti"e error.



77/459

77

Test.,ava5 "et#odneB/ is already defined in Test


verloadin! +on+ept is appli+able for stati+ "et#od in+l(din! "ain "et#od also.Example:

In#eritan+e +on+ept is appli+able for stati+ "et#ods in+l(din! "ainB/ "et#od #en+e w#ileeEe+(tin! +#ild +lass- if t#e +#ild doesnt +ontain "ainB/ "et#od t#en t#e parent +lass "ain"et#od will be eEe+(ted.

Example:

+lass \arent


Cyste".o(t.printlnBNparent "ainB/ "et#od +alledN/9

=

=


=

!utput:

Example:

!utput:


78/459

7$

It see"s to be overridin! +on+ept is appli+able for stati+ "et#ods b(t it is not overridin! it is"et#od #idin!.

Hor stati+ "et#ods +o"p(lsory i"ple"entation s#o(ld be available w#ere as for abstra+t"et#ods i"ple"entation s#o(ld be available #en$e a,stra$t stati$ $om,ination is illegal for

met#ods9

/ative modifier:

:ative is a "odifier appli+able only for "et#ods b(t not for variables and +lasses. T#e "et#ods w#i+# are i"ple"ented in non ,ava are +alled native "et#ods or forei!n "et#ods.

8#e main o,je$tives of native +e(%ord are:

To i"prove perfor"an+e of t#e syste". To (se already eEistin! le!a+y non ,ava +ode.

8o use native +e(%ord:

seudo $ode:

Hor native "et#ods i"ple"entation is already available and we are not responsible toprovide i"ple"entation #en+e native "et#od de+laration s#o(ld +o"p(lsory ends wit#

se"i+olon.

\(bli+ native void "et#odneB/invalid \(bli+ native void "et#odneB/9valid


79/459

7&

Hor native "et#ods i"ple"entation is already available w#ere as for abstra+t "et#odsi"ple"entation s#o(ld not be available +#ild +lass is responsible to provide t#at- #en+e

abstra+t native +o"bination is ille!al for "et#ods. @e +ant de+lare a native "et#od as stri+tfp be+a(se t#ere is no !(aranty w#et#er t#e

old lan!(a!e s(pports I


80/459


81/459

$1

b/ ariable na"in! +onfli+ts7/ %ar?er interfa+e$/ Adapter +lass&/ Interfa+e vs abstra+t +lass vs +on+rete +lass.1)/Differen+e between interfa+e and abstra+t +lassW11/'on+l(sions

'ef1:Any servi+e reV(ire"ent spe+ifi+ation Bsrs/ is +alled an interfa+e.

Example1: C(n people responsible to define *D' A\I and database vendor will provide

i"ple"entation for t#at.

'iagram:

Example2:C(n people define C


82/459

$2

ummer( def:Any servi+e reV(ire"ent spe+ifi+ation BCRC/ or any +ontra+t between +lient and

servi+e provider or 1))` p(re abstra+t +lasses is +onsidered as an interfa+e.

'e$laration and implementation of an interfa$e::ote1 @#enever we are i"ple"entin! an interfa+e $ompulsor( for ever( met#od of t#at

interfa$e %e s#ould provide implementation ot#er%ise %e #ave to de$lare $lass as a,stra$tin

t#at +ase $#ild $lass is responsi,le to provide implementation for remaining met#ods.

:ote2 @#enever we are i"ple"entin! an interfa+e "et#od $ompulsor( it s#ould ,e de$lared

as pu,li$ ot#er%ise %e %ill get $ompile time error.

Example:

interfa+e Interf

void "et#odneB/9void "et#odTwoB/9

=

+lass C(bCervi+e\rovider eEtends Cervi+e\rovider

=

!utput:

'o"pile ti"e error.

DY*ava,ava+ C(bCervi+e\rovider.,ava

C(bCervi+e\rovider.,ava1 C(bCervi+e\rovider is not abstra+t and does not override abstra+t

"et#od "et#odTwoB/ in Interf

+lass C(bCervi+e\rovider eEtends Cervi+e\rovider

Extends vs implements:

A +lass +an eEtend only one +lass at a ti"e.Example:

+lass ne


=

=

+lass Two eEtends ne

=

A +lass +an i"ple"ents any no. f interfa+es at a ti"e.


83/459

$3

Example:

interfa+e ne

p(bli+ void "et#odneB/9=

interfa+e Two

p(bli+ void "et#odTwoB/9

=

+lass T#ree i"ple"ents ne-Two


=

p(bli+ void "et#odTwoB/

==

A +lass +an eEtend a +lass and +an i"ple"ent an interfa+e si"(ltaneo(sly.interfa+e ne

void "et#odneB/9

=

+lass Two

p(bli+ void "et#odTwoB/

==

+lass T#ree eEtends Two i"ple"ents ne


=

=

An interfa+e +an eEtend any no. f interfa+es at a ti"e.Example:

interfa+e ne

void "et#odneB/9=

interfa+e Two

void "et#odTwoB/9

=

interfa+e T#ree eEtends ne-Two

=

1; "#i$# of t#e follo%ing is true&


84/459

$4

1. A +lass +an eEtend any no. f +lasses at a ti"e.2. An interfa+e +an eEtend only one interfa+e at a ti"e.3. A +lass +an i"ple"ent only one interfa+e at a ti"e.4. A +lass +an eEtend a +lass and +an i"ple"ent an interfa+e b(t not bot#

si"(ltaneo(sly.

5. :one of t#e above.Ans 5

2/ 'onsider t#e eEpression D extends J for w#i+# of t#e possibility of P and t#iseEpression is tr(eW

1. ot# E and y s#o(ld be +lasses.2. ot# E and y s#o(ld be interfa+es.3. ot# E and y +an be +lasses or +an be interfa+es.4. :o restri+tion.

Ans 3

3; D extends JH K& P- - s#o(ld be interfa+es.

4; D extends J implements K& P- s#o(ld be +lasses. s#o(ld be interfa+e.

5; D implements JH K& P s#o(ld be +lass. - s#o(ld be interfa+es.

6; D implements J extend K&Example:

interfa+e ne

=

+lass Two

=

+lass T#ree i"ple"ents ne eEtends Two

=!utput:

'o"pile ti"e error.

DY*ava,ava+ T#ree.,ava

T#ree.,ava5 QQ eEpe+ted

+lass T#ree i"ple"ents ne eEtends Two


85/459

$5

p(bli+ oid "et#odneB/9

abstra+t oid "et#odneB/9 EAual

p(bli+ abstra+t oid "et#odneB/9 As every interfa+e "et#od is always p(bli+ and abstra+t we +ant (se t#e followin!

"odifiers for interfa+e "et#ods.

rivateH prote$tedH finalH stati$H s(n$#roniedH nativeH stri$tfp9Inside interfa$e %#i$# met#od de$larations are valid&

1. p(bli+ void "et#odneB/=2. private void "et#odneB/93. p(bli+ final void "et#odneB/94. p(bli+ stati+ void "et#odneB/95. p(bli+ abstra+t void "et#odneB/9

Ans 5

Interfa$e varia,les:

An interfa+e +an +ontain variables to define reV(ire"ent level +onstants.


86/459

$6

Transient olatile

Hor t#e interfa+e variables +o"p(lsory we s#o(ld perfor" initiali0ation at t#e ti"e ofde+laration only ot#erwise we will !et +o"pile ti"e error.

Example:

interfa+e Interf

int E9

=

!utput:

'o"pile ti"e error.

DY*ava,ava+ Interf.,avaInterf.,ava3 8 eEpe+ted

int E9

"#i$# of t#e follo%ing de$larations are valid inside interfa$e&

1. int E92. private int E81)93. p(bli+ volatile int E81)94. p(bli+ transient int E81)95. p(bli+ stati+ final int E81)9

Ans 5 Interfa+e variables +an be a++ess fro" i"ple"entation +lass b(t +annot be "odified.

Example:

interfa+e Interf

int E81)9

=

Example 1:


87/459

$7

Example 2:

+lass Test i"ple"ents Interf


int E82)9

JJ#ere we de+larin! t#e variable E.


=

=

!utput:


DY*ava,ava Test2)

Interfa$e naming $onfli$ts:

=et#od naming $onfli$ts:

*ase 1:

If two interfa+es +ontain a "et#od wit# sa"e si!nat(re and sa"e ret(rn type in t#ei"ple"entation +lass only one "et#od i"ple"entation is eno(!#.

Example 1:

interfa+e Left

p(bli+ void "et#odneB/9

=

Example 2:

interfa+e Ri!#t


=

Example 3:

+lass Test i"ple"ents Left-Ri!#t


==

!utput:

DY*ava,ava+ Left.,ava

DY*ava,ava+ Ri!#t.,ava



88/459

$$

*ase 2:

if two interfa+es +ontain a "et#od wit# sa"e na"e b(t different ar!("ents in t#ei"ple"entation +lass we #ave to provide i"ple"entation for bot# "et#ods and t#ese"et#ods a+ts as a overloaded "et#ods

Example 1:

interfa+e Left


=

Example 2:

interfa+e Ri!#t

p(bli+ void "et#odneBint i/9

=

Example 3:

+lass Test i"ple"ents Left-Ri!#t


=

p(bli+ void "et#odneBint i/

==

!utput:

DY*ava,ava+ Left.,ava



*ase 3:

If two interfa+es +ontain a "et#od wit# sa"e si!nat(re b(t different ret(rn types t#enit is not possible to i"ple"ent bot# interfa+es si"(ltaneo(sly.

Example 1:

interfa+e Left


=

Example 2:

interfa+e Ri!#t


89/459

$&

p(bli+ int "et#odneBint i/9

=

@e +ant write any ,ava +lass t#at i"ple"ents bot# interfa+es si"(ltaneo(sly.Is a ,ava +lass +an i"ple"ent any no. f interfa+es si"(ltaneo(slyW

es- eE+ept if two interfa+es +ontains a "et#od wit# sa"e si!nat(re b(t different ret(rntypes.

-aria,le naming $onfli$ts:

Two interfa+es +an +ontain a variable wit# t#e sa"e na"e and t#ere "ay be a +#an+evariable na"in! +onfli+ts b(t we +an resolve variable na"in! +onfli+ts by (sin! interfa+e

na"es.

Example 1:

interfa+e Left

int E8$$$9

=

Example 2:

interfa+e Ri!#t

int E8&&&9

=

Example 3:+lass Test i"ple"ents Left-Ri!#t


JJCyste".o(t.printlnBE/9

Cyste".o(t.printlnBLeft.E/9

Cyste".o(t.printlnBRi!#t.E/9

=

=

!utput:DY*ava,ava+ Left.,ava



DY*ava,ava Test

$$$

&&&


90/459

&)

=ar+er interfa$e: if an interfa+e doesnt +ontain any "et#ods and by i"ple"entin! t#at

interfa+e if o(r ob,e+t !ets so"e ability s(+# type of interfa+es are +alled %ar?er interfa+e Bor/

Ta! interfa+e Bor/ Ability interfa+e.Example:

Cerili0able

+loneable

Rando"A++ess T#ese are "ar?ed for so"e ability

Cin!leT#read%odel

.

.

.

.Example 1:y i"ple"entin! Cerili0able interfa+e we +an send t#at ob,e+t a+ross t#e networ?

and we +an save state of an ob,e+t into a file.

Example 2:y i"ple"entin! Cin!leT#read%odel interfa+e Cervlet +an pro+ess only one +lient

reV(est at a ti"e so t#at we +an !et KT#read Cafety.

Example 3:y i"ple"entin! 'loneable interfa+e o(r ob,e+t is in a position to provide eEa+tly

d(pli+ate +loned ob,e+t.

"it#out #aving an( met#ods in mar+er interfa$e #o% o,je$ts %ill get a,ilit(&

Internally *% will provide reV(ired ability."#( 0-= is providing t#e reAuired a,ilit(&

To red(+e +o"pleEity of t#e pro!ra""in!.Is it possi,le to $reate our o%n mar+er interfa$e&

es- b(t +(sto"i0ation of *% is reV(ired.7dapter $lass:

Adapter +lass is a si"ple ,ava +lass t#at i"ple"ents an interfa+e only wit# e"ptyi"ple"entation for every "et#od.

If we i"ple"ent an interfa+e dire+tly for ea+# and every "et#od +o"p(lsory we s#o(ldprovide i"ple"entation w#et#er it is reV(ired or not. T#is approa+# in+reases len!t# of

t#e +ode and red(+es readability.Example 1:

interfa+e P

void "1B/9

void "2B/9

void "3B/9

void "4B/9

JJ.

JJ.


91/459

&1

JJ.

JJ.

void "5B/9=

Example 2:

+lass Test i"ple"ents P

p(bli+ void "3B/

Cyste".o(t.printlnBN"3B/ "et#od is +alledN/9

=

p(bli+ void "1B/=

p(bli+ void "2B/=

p(bli+ void "4B/=p(bli+ void "5B/=

=

@e +an resolve t#is proble" by (sin! adapter +lass. Instead of i"ple"entin! an interfa+e if we +an eEtend adapter +lass we #ave to provide

i"ple"entation only for reV(ired "et#ods b(t not for all "et#ods of t#at interfa+e.

T#is approa+# de$reases lengt# of t#e $odeand i"proves readability.Example 1:

abstra+t +lass AdapterP i"ple"ents P

p(bli+ void "1B/=p(bli+ void "2B/=

p(bli+ void "3B/=

p(bli+ void "4B/=

JJ.

JJ.

JJ.

p(bli+ void "1)))B/=

=

Example 2:p(bli+ +lass Test eEtend AdapterP

p(bli+ void "3B/

==

Example:


92/459

&2

^eneri+ Cervlet si"ply a+ts as an adapter +lass for Cervlet interfa+e."#at is t#e differen$e ,et%een interfa$eH a,stra$t $lass and $on$rete $lass&

"#en %e s#ould go for interfa$eH a,stra$t $lass and $on$rete $lass&

If we dont ?now anyt#in! abo(t i"ple"entation ,(st we #ave reV(ire"entspe+ifi+ation t#en we s#o(ld !o for interfa+e.

If we are tal?in! abo(t i"ple"entation b(t not +o"pletely Bpartial i"ple"entation/t#en we s#o(ld !o for abstra+t +lass.

If we are tal?in! abo(t i"ple"entation +o"pletely and ready to provide servi+e t#en wes#o(ld !o for +on+rete +lass.

Example:

"#at is t#e 'ifferen$e ,et%een interfa$e and a,stra$t $lass&

interfa+e Abstra+t +lass1/ If we dont ?now anyt#in! abo(t

i"ple"entation ,(st we #ave

reV(ire"ent spe+ifi+ation t#en we

s#o(ld !o for interfa+e.

1/ If we are tal?in! abo(t i"ple"entationb(t not +o"pletely Bpartial

i"ple"entation/ t#en we s#o(ld !o for

abstra+t +lass.

2/


93/459

&3

wit# t#e "odifiers private- prote$ted-

final- stati$- s(n$#ronied- native-

stri$tfp.

+lass "et#od "odifiers.

4/


94/459

&4

Ever( met#od present inside interfa$e is a,stra$t ,ut in a,stra$t $lass also %e $an ta+e onl(

a,stra$t met#ods t#en %#at is t#e need of interfa$e $on$ept&

@e +an repla+e interfa+e +on+ept wit# abstra+t +lass. (t it is not a !ood pro!ra""in!pra+ti+e. @e are "is(sin! t#e roll of abstra+t +lass.

!perator and assignments1/ In+re"ent and de+re"ent operator2/ Arit#"eti+ operators3/ Ctrin! +on+atenation operator4/ Relational operators5/


95/459

&5

&/ Type +ast operator1)/Assi!n"ent operator11/'onditional operator12/new operator13/> operator14/*ava operator pre+eden+e15/


96/459

&6

:estin! of in+re"ent or de+re"ent operators is not allowed.Example:

@e +ant apply in+re"ent or de+re"ent operator for final variables.Example:

@e +an apply in+re"ent or de+re"ent operator for any pri"itive type eE+ept oolean.Example:


97/459

&7

If we apply any arit#"eti+ operator between two variables Ka and Kb t#e res(lt type isalways.

maxintHt(peof aHt(peof ,;

Example 1:

Example 2:

In t#e +ase of in+re"ent or de+re"ent operator t#e reV(ired type+astin! will beperfor"ed a(to"ati+ally by t#e +o"piler.

Example:

byte b81)9

bFF9

Cyste".o(t.printlnBb/9JJ11

7rit#meti$ operators:BF--U- J- `/


98/459

&$

If we apply any arit#"eti+ operation between two variables Ka and Kb. T#e res(lt typeis always.

maxintH t(pe of aH t(pe ,;

Example:

Cyste".o(t.printlnBQaQF1/9JJ&$

Cyste".o(t.printlnBQaQFQbQ/9JJ1&5

Cyste".o(t.printlnB1)F).5/9JJ1).5Cyste".o(t.printlnBQaQF3.5/9JJ1)).5

Infinit(:

In t#e +ase of inte!ral arit#"eti+ Bbyte- s#ort- int- lon!/ t#ere is no way to representinfinity.

Sen+e if infinity is t#e res(lt t#en we will !et Arit#"eti+


99/459

&&

Sen+e if t#e res(lt is (ndefined- we wont !et any r(nti"e eE+eption in floatin! pointarit#"eti+.

Example:Cyste".o(t.printlnB).)J)/9JJ:a:

Cyste".o(t.printlnB).)J)/9JJ:a:

Cyste".o(t.printlnB)J).)/9JJ:a:

Hor any xval(e in+l(din! /a/t#e followin! eEpressions ret(rn false.Example:

+lass Test


int E81)9

Cyste".o(t.printlnBEHloat.:a:/9JJfalse

Cyste".o(t.printlnBEZHloat.:a:/9JJfalse

Cyste".o(t.printlnBE8Hloat.:a:/9JJfalse

Cyste".o(t.printlnBEZ8Hloat.:a:/9JJfalse

Cyste".o(t.printlnBE88Hloat.:a:/9JJfalse

=

=

Hor any xval(e in+l(din! /a/t#e followin! eEpression ret(rn tr(e.Example:

+lass Test


int E81)9

Cyste".o(t.printlnBE8Hloat.:a:/9JJtr(e

Cyste".o(t.printlnBHloat.:a:8Hloat.:a:/9JJtr(e

==

ummar(:


100/459

1))

tring $on$atenation operator:

T#e only operator w#i+# is overloaded in ,ava is K? operator. Co"eti"e it a+ts asarit#"eti+ addition operator and so"e ti"e +on+atenation operator.

If at least one ar!("ent is strin! type t#en K? operator a+ts as +on+atenation and ifbot# ar!("ents are n("ber type t#en it a+ts as arit#"eti+ addition operator.

Example 1:

Ctrin! a8Nb#as?arN9

int b81)-+82)-d83)9

Cyste".o(t.printlnBaFbF+Fd/9JJb#as?ar1)2)3)

Cyste".o(t.printlnBbF+FdFa/9JJ6)b#as?ar

Cyste".o(t.printlnBbF+FaFd/9JJ3)b#as?ar3)

Cyste".o(t.printlnBbFaF+Fd/9JJ1)b#as?ar2)3)Example 2:

Example 3:

Relational operator:H MH NH NM;

@e +an apply relational operators for every pri"itive type eE+ept boolean.Example:

@e +ant apply relational operators for t#e ob,e+t types.Example:


101/459

1)1

@e +ant perfor" nestin! of relational operators.Example:

EAualit( operator :B88-8/

@e +an apply eV(ality operators for every pri"itive type in+l(din! boolean type also.Example:

Cyste".o(t.printlnB1)881).)/9JJtr(e

Cyste".o(t.printlnBQaQ88&7.)/9JJtr(e

Cyste".o(t.printlnBtr(e88tr(e/9JJtr(e

Cyste".o(t.printlnBQaQ8QbQ/9JJtr(e @e +an apply eV(ality operator even for ob,e+t referen+e also. In t#e +ase of ob,e+t referen+es 88 Bdo(ble eV(al operator/ is always "eant for

referen+e +o"parison only Baddress +o"parison/.

i.e. r188r2 ret(rn tr(e if and only if bot# r1 and r2 point to t#e sa"e ob,e+t.Example:

T#read t18new T#readB/9


T#read t38t19Cyste".o(t.printlnBt188t2/9JJfalse

Cyste".o(t.printlnBt188t3/9JJtr(e

'iagram:

To (se eV(ality operator +o"p(lsory t#ere s#o(ld be so"e relations#ip betweenar!("ent typeBeit#er parent+#ild Bor/+#ildparent Bor/ sa"e type/ot#erwise we will !et

+o"pile ti"e error sayin! in+o"parable types.Example:

b,e+t o8new b,e+tB/9

Ctrin! s8new Ctrin!BNb#as?arN/9

Ctrin!(ffer sb8new Ctrin!(fferB/9

Cyste".o(t.printlnBo88s/9JJfalse

Cyste".o(t.printlnBo88sb/9JJfalse


102/459

1)2

'iagram:

Hor any ob,e+t referen+e of- r88n(ll is always false. (t n(ll88n(ll is tr(e.MM -s 9eAuals;:

88operator is always "eant for referen+e +o"parison w#ereas .eV(alsB/ "et#od "ostly"eant for +ontent +o"parison.

Example:



Cyste".o(t.printlnBs188s2/9JJfalse

Cyste".o(t.printlnBs1.eV(alsBs2//9JJtr(e

'iagram:

Instan$eof operator: @e +an (se t#is operator to +#e+? w#et#er t#e !iven ob,e+t is of parti+(lar type Bor/ not.

(ntax:

Example:


Cyste".o(t.printlnBt instan+eof T#read/9JJtr(e

Cyste".o(t.printlnBt instan+eof b,e+t/9JJtr(e

Cyste".o(t.printlnBt instan+eof R(nnable/9JJtr(e

'iagram:

/ote:


103/459

1)3

To (se Kinstan+eof operator +o"p(lsory t#ere s#o(ld be so"e relations#ip betweenar!("ent types Beit#er parent+#ild Bor/ +#ildparent Bor/ sa"e type/ ot#erwise we will

!et +o"pile ti"e error sayin! Kin+onvertible types.Example:

@#enever we are +o"parin! parent ob,e+t is +#ild type or not by (sin! instan+eofoperator t#en we will !et Kfalse as o(tp(t.

Example:b,e+t o8new b,e+tB/9

Cyste".o(t.printlnBo instan+eof Ctrin!/9JJfalse

Hor any +lass or interfa+e Enull instan$eof x t#e res(lt is always Kfalse.

Example:

Cyste".o(t.printlnBn(ll instan+eof Ctrin!/9JJfalse

it%ise operators:

O 7/';: If bot# ar!("ents are tr(e t#en res(lt is tr(e.

P !R;:if at least one ar!("ent is tr(e. T#en t#e res(lt is tr(e.Q D

Cyste".o(t.printlnBtr(eOfalse/9JJtr(e

Cyste".o(t.printlnBtr(efalse/9JJtr(e

@e +an apply bitwise operators even for inte!ral types also.Example:

it%ise $omplement ; tilde s(m,ol; operator:

@e +an apply t#is operator only for inte!ral types b(t not for boolean types.Example 1:

Example 2:


104/459

1)4

Cyste".o(t.printlnB4/9JJ5

'iagram:

oolean $omplement S; operator:

T#is operator is appli+able only for boolean types b(t not for inte!ral types.Example:

Cyste".o(t.printlnBtr(e/9JJfalse

Cyste".o(t.printlnBfalse/9JJtr(e

ummar(:

c

O Appli+able for bot# boolean and inte!ral types.

Appli+able for inte!ral types only.

Appli+able for boolean types only.

#ort $ir$uit OOH PP; operators:

T#ese operators are eEa+tly sa"e as nor"al bitwise operators c- O eE+ept t#e followin!differen+es.

OHP OOHPP

1/ ot# ar!("ents s#o(ld be eval(atedalways.

1/ Ce+ond ar!("ent eval(ation isoptional.

2/ Relatively perfor"an+e is low. 2/ Relatively perfor"an+e is #i!#.3/ Appli+able for bot# inte!ral and

boolean types.

3/ Appli+able only for boolean types b(tnot for inte!ral types.

1; r1OOr2 r2 will be eval(ated if and only if r1 is tr(e.2; r1PPr2 r2 will be eval(ated if and only if r1 is false.

Example 1:

+lass peratorsDe"o


105/459

1)5


int E81)- y8159

ifBFFE1)Boperator/FFyZ15/

FFE9

=

else

FFy9

=Cyste".o(t.printlnBEFNNFy/9

=

=

!utput:

operator x (

c 11 17

O 12 16

cc 11 17

OO 12 15

Example 2:

+lass peratorsDe"o


int E81)9

ifBFFEZ1)Boperator/EJ)1)/


=

else

Cyste".o(t.printlnBN#iN/9

=

=

=

OO !utput:Si

O !utput:R.


106/459

1)6

,ava.lan!.Arit#"eti+


107/459

1)7

Example 2:

int E813)9

byte b8Bbyte/E9

Cyste".o(t.printlnBb/9JJ126

7nal(sis:

@#enever we are assi!nin! bi!!er data type val(e to t#e s"aller data type variable byeEpli+it type +astin! t#e "ost si!nifi+ant bitB%C/will be lost.

Example:

int E815)9

s#ort s8Bs#ort/E9

Cyste".o(t.printlnBs/9JJ15)

byte b8Bbyte/E9

Cyste".o(t.printlnBb/9JJ1)6

@#enever we are assi!nin! floatin! point data types to t#e inte!er data type by eEpli+ittype +astin! t#e di!its after t#e de+i"al point will be loosed.

Example:

7ssignment operators:

T#ey are t#ree types of assi!n"ent operators.imple assignment:


108/459

1)$

Example: int E81)9

*#ained assignment:

Example:int a-b-+-d9

a8b8+8d82)9

Cyste".o(t.printlnBaFNNFbFNNF+FNNFd/9JJ2)2)2)2)

@e +ant perfor" +#ained assi!n"ent dire+tly at t#e ti"e of de+laration.Example 1:

Example 2:

int a-b-+-d9

a8b8+8d83)9

*ompound assignment:

Co"eti"es we +an "iE assi!n"ent operator wit# so"e ot#er operator to for"+o"po(nd assi!n"ent operator.

T#e followin! is t#e list of all possible +o"po(nd assi!n"ent operators in ,ava.Example 1:

In t#e +ase of +o"po(nd assi!n"ent operator t#e reV(ired type +astin! will beperfor"ed a(to"ati+ally by t#e +o"piler si"ilar to in+re"ent and de+re"ent

operators.

Example 2:

Example 3:


109/459

1)&

*onditional operator:

T#e only ternary operator w#i+# is available in ,ava is +onditional operator.Example 1:

int E8B1)2)/W3)4)9

Cyste".o(t.printlnBE/9JJ4)

@e +an perfor" nestin! of +onditional operator also.Example 2:

Example 5:

Example 6:

final int a81)-b82)9

byte +18Bab/W3)4)9

byte +28BaZb/W3)4)9

Cyste".o(t.printlnB+1/9JJ4)

Cyste".o(t.printlnB+2/9JJ3)ne% operator:

@e +an (se Knew operator to +reate an ob,e+t. T#ere is no Kdelete operator in ,ava be+a(se destr(+tion of ob,e+ts is t#e responsibility

of !arba!e +olle+tor.

TU operator:

@e +an (se t#is operator to de+lare and +onstr(+t arrays.0ava operator pre$eden$e:

.nar( operators:


110/459

11)

>- EFF- P-

FFE-E- --

new- Ztype.7rit#meti$ operators:

U-J-`-

F-.

#ift operators:

--ZZ.

*ompression operators:

Z- Z8--8- instan+eof.

EAualit( operators:

88-8it%ise operators:

c--O.

#ort $ir$uit operators:

cc-OO.

*onditional operator:

BW/

7ssignment operators:

F8-8-U8-J8-`8.

Evaluation order of java operands: T#ere is no pre+eden+e for operands before applyin! any operator all operands will be

eval(ated fro" left to ri!#t.

Example:

+lass peratorsDe"o


Cyste".o(t.printlnB"1B1/F"1B2/U"1B3/J"1B4/U"1B5/F"1B6//9

=p(bli+ stati+ int "1Bint i/


ret(rn i9

=

=


111/459

111

Example 1:

Example 2:int i819

iF8FFi F iFF F FFi F iFF9

Cyste".o(t.printlnBi/9JJ13Analysis

i8iF FFi F iFF F FFi F iFF9

i81F2F2F4F49

i8139


112/459

112

Flo% *ontrol Hlow +ontrol des+ribes t#e order in w#i+# all t#e state"ents will be eEe+(ted at r(n

ti"e.

'iagram:

ele$tion statements:

19 if/

int E8)9

ifBE/


=else


===

!.8.8:

'o"pile ti"e error

DY*ava,ava+


113/459

113


int E81)9

ifBE82)/


=else


===

!.8.8:

'o"pile ti"e error

DY*ava,ava+


114/459

114


=else


===

!.8.8:

Si

ot# elseand $url( ,ra$esare optional. @it#o(t +(rly bra+es we +an ta?e only one state"ent (nder if- b(t it s#o(ld not be

de+larative state"ent.

ED7=LE 6:

p(bli+ +lass /

ifBtr(e/Cyste".o(t.printlnBN#elloN/9

==

!.8.8:

Sello

ED7=LE :

p(bli+ +lass /

ifBtr(e/9

==

!.8.8::o o(tp(t

ED7=LE B:

p(bli+ +lass /

ifBtr(e/

int E81)9

==

!.8.8:

'o"pile ti"e error

DY*ava,ava+ /

ifBtr(e/

int E81)9

===


115/459

115

!.8.8:

DY*ava,ava+ /

swit+#BE/


===


116/459

116

!.8.8:

'o"pile ti"e error.

DY*ava,ava+


117/459

117

final int y82)9

swit+#BE/

+ase 1)

Cyste".o(t.printlnBN1)N/9

+ase y

Cyste".o(t.printlnBN2)N/9

===

!.8.8:

1)

2)

Cwit+# ar!("ent and +ase label +an be eEpressions also- ,ut $ase s#ould ,e $onstantexpression9

ED7=LE 4:p(bli+ +lass /

int E81)9

swit+#BEF1/

+ase 1)

+ase 1)F2)

+ase 1)F2)F3)

===

!.8.8::o o(tp(t.


118/459

11$

reV(ired byte

+ase 1)))

D(pli+ate +ase labels are not allowed.ED7=LE 6:

p(bli+ +lass /

int E81)9

swit+#BE/

+ase &7

Cyste".o(t.printlnBN&7N/9

+ase &&

Cyste".o(t.printlnBN&&N/9

+ase QaQCyste".o(t.printlnBN1))N/9===

!.8.8:

'o"pile ti"e error.

DY*ava,ava+


119/459

11&

Cyste".o(t.printlnBN)N/9

+ase 1

Cyste".o(t.printlnBN1N/9

brea?9

+ase 2


defa(lt

Cyste".o(t.printlnBNdefa(ltN/9

===

!.8.8:

DM xM1 xM2 xM3

) 1 2 defa(lt

1 defa(lt

'EF7.L8 *7E: @it#in t#e swit+# we +an ta?e t#e defaultanyw#ere- b(t at "ost on+e it is +onvention

to ta?e defa(lt as last +ase.

ED7=LE B:

p(bli+ +lass /

int E8)9

swit+#BE/

defa(lt

Cyste".o(t.printlnBNdefa(ltN/9+ase )

Cyste".o(t.printlnBN)N/9

brea?9

+ase 1


+ase 2


===

!.8.8:

DM xM1 xM2 xM3

) 1 2 defa(lt

2 )

I8ER78I-E 878E=E/8:

"#ile loopif we dont ?now t#e no of iterations in advan+e t#en best loop is w#ile loopED7=LE 1:

w#ileBrs.neEtB//

=


120/459

12)

ED7=LE 2:

w#ileBe.#as%oreel/

w#ileBtr(e/


==

!.8.8:

Sello Binfinite ti"es/.


121/459

121

ED7=LE 3:

p(bli+ +lass /w#ileBtr(e/9

==

!.8.8:

:o o(tp(t.

ED7=LE 4:

p(bli+ +lass /

w#ileBtr(e/

int E81)9==

!.8.8:

'o"pile ti"e error.

DY*ava,ava+ /

w#ileBtr(e/

int E81)9

===

!.8.8:

:o o(tp(t.

;nrea+#able state"ent in w#ileED7=LE 6:

p(bli+ +lass /

w#ileBtr(e/


=



122/459

122

==

!.8.8:

'o"pile ti"e error.DY*ava,ava+ /

w#ileBfalse/

Cyste".o(t.printlnBN#elloN/9=


==

!.8.8:

DY*ava,ava+ /

final int a81)-b82)9

w#ileBaZb/



123/459

123

=


==!.8.8:

'o"pile ti"e error.

DY*ava,ava+ /

final int a81)9w#ileBaZ2)/


=


==

!.8.8:

DY*ava,ava+


124/459

124

!.8.8:


'o


125/459

125

!utput:

DY*ava,ava+ /do w#ileBtr(e/


w#ileBtr(e/9

==

!utput:


Rearrange t#e a,ove example:

p(bli+ +lass /do

w#ileBtr(e/


w#ileBtr(e/9

==

!utput:



126/459

126

Example 6:

p(bli+ +lass /do

w#ileBtr(e/9

==

!utput:

'o"pile ti"e error.

DY*ava,ava+


127/459

127

==

!utput:

SelloSi

Example V:

p(bli+ +lass /

int a81)-b82)9

do


=w#ileBaZb/9


==

!utput:


Example 1:

p(bli+ +lass /

int a81)-b82)9do

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