Interface and Collections

8/18/2019 Interface and Collections

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nterface & Collections

Defnition : "An inteace is a named collection o related abstractmembers".

nterace is defned in C# by using the keyword "interace".

nterace's are not associated with base class not e!en ystem.b$ect% & containsmembers that has no access modifers.

nterace methods are imlicitly ublic( in order to allow suorting tye tomlement members.

).*: interace +interace name,-

ember declarations /

n addition to methods interaces can ha!e roerties( e!ents & inde0ers.

10: interace I10amle -

!oid Dislay%2int Aroerty

- get2 / /

C# classes3structures can inherit rom interaces as shown below.class stud:I10amle struct stud:I10amle-.../ -.../4

more than one interaces are inherited then they are listed using comma

searated list.class stud:I10amle( I10amle5-.../

classe's are imlicitly deri!ed rom ystem.b$ect & structures are deri!ed romystem.6alue7ye. I there is any e0licit inheritance on the class to be done( thenhe name o it must be listed frst & then interace names.

class stud:89( I10amle5-.../

hen interaces are inherited then all the members in it must be comulsorilydefned by the inherting entity. 7he inheriting entity has no choice on choosing themembers to imlement.10:

class pgm:DM,IAdd,IMul {

public void read() {

a = int.Parse(Console.rite!ine())"

b = int.Parse(Console.rite!ine())"

#

$$ met%od o& inter&ace IAdd public void add() {

Console.rite!ine(a'b)"

#

public void mul() {

Console.rite!ine(ab)"

#

public static void Main()

{

pgm a = ne pgm()"

a.read()"

a.add()" a.mul()" #

#

using *+stem"

inter&ace IAdd

{

void add()"

#

inter&ace IMul

{

void mul()"

#

class DM

{

protected int a,b"

#

1


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Abstract class & Interaces are in contrast to each other.

Abstract class can defne ublic( ri!ate & rotected data members whichnterace's cannot ha!e within them.

Abstract classe's can ha!e any number o concrete methods that can be accessedby subclasses. ;ut no defnition o methods is allowed in interaces. 1!erymember o an interace is automatically abstract.

C# suorts only single inheritance i.e one class can ha!e only one base class%.


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class gm:IAdd- int a(b2 ublic gmint 0( int y% - a=02b=y2/ ublic int add% - return a>b%2 //

class 10- ublic static !oid ain% - IAdd r2 gm a = new gm%2 r = IAdd% a2 33 10licit casting Console.rite?iner.add%%2 //

is a reerence o interace. icne( class gm suorts the interace Add e0licitcasting is ossible & using r( add% method can be in!oked.

class gm does not imlement interace add% then e0licit casting lilnegenerates run time error & throws an "In!alidCast10cetion".using r( only the methods in interace can be in!oked. ethods ertaining to classgm cannot be in!oked.

2) obtaining reference via 'as' keyword

10: IAdd r2 gm a = new gm%2 r = a as IAdd2 r.add%2

using 'as' keyword e0licit casting can be done as shown.

class gm imlements methods in the interace then ob$ect a is casted to r. I

class gm doesn't imlement methods in the interace then( as line laces a null!alue into r rather than throwing any e0cetions.

3) Checking interface ipleentation via 'is' keyword

10:gm a = new gm%2i a is IAdd%Console.rite?inea.add%%2

3


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Derived class; must override getpoint()

Abstract class; int getpoint(); Returns number of points for a shapeShape

Triangle

e!agon

"ircle

elseConsole.rite?ine"gm doesnt imlement add%"%2

a is not add% method comatible then condition ails.

nterfaces as paraeters

As shown abo!e in method dis2 arameter is an interace entity. nly thenstances o a class which imlements IAdd interace can be assed as argumentsnto it.

imilarly interace reerence can be used as a return tye o a method.

nterface as polyorphic agents

class pgm

{

static void disp(IAdd r)

$$ parameter t+pe is re&erence o&

$$ inter&ace t+pe

{ r.add()" #

public static void Main()

{

Aint a = ne Aint(-,)"

As%ort b = ne As%ort(/,0)"

disp(a)"

disp(b)"

$$ arguments are instances o& a cla

$$%ic% implement inter&aces

#

#

inter&ace IAdd

{ void add()" #

class Aint:IAdd

{

int a,b"

public Aint(int 1, int +)

{ a=1" b=+"#

public void add()

{ Console.rite!ine(2{3#2,(a'b))" #

#

class As%ort"IAdd

{

s%ort a,b"

public As%ort(s%ort 1, s%ort +)

{ a=1" b=+"#

public void add()

{Console.rite!ine(2{3#2,(a'b))" #

#

#


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"ontains a method int getpoint ();$Shape

Triangle e!agon "ircle

hae is an abstract class that defnes beha!iour common or its deri!ed class.7riangle( @e0agon & Circle are deri!ed class o shae & getoint% must becomulsorily defned in these classes.

7riangle & @e0agon are caable o defning this method but circle does not needhis method. Drawback o abstract class is that all deri!ed tyes must defne the

abstract method. 9ow consider shae as interace

As shown 7riangle & @e0agon imlements Ihae & Circle doesn't imlement it.e!eral other class hierarchies can also inherit rom interaces & they canmlement them.

Explicit Interface ipleentation

10:abstract class b interace IAdd

- ublic abstract !oid add%2 / - !oid add%2/

class Aint:b(IAdd- int a(b2 ... ublic o!erride !oid add% -...//

Aint a = new Aint%2

a.add%2IAdd r = IAdd% a2r.add%2

Considering the e0amle both abstract class b & interace IAdd has an abstractmethod add %. Class Aint inherits rom b & IAdd. add% method has beeno!erriden in Aint.

add% method is in!oked !ia instance o class Aint or !ia reerence o IAdd sameadd% method will be in!oked. 9ecessity o ha!ing add% methods is to ha!ediBerent unctionalities in diBerent method.

10: add% in abstract class can add no's & see whether theresult is e!en or not.add% in interace can $ust add no's

7o diBerentiate between the method o abstract class & the method o interaceexplicit interface ipleentation" must be used.

%


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class Aint:b(IAdd-

int a(b2

...!oid I!dd"add% 33 10licit interace imlementation-Console.rtie?ine"Interace add"%2/ublic o!erride !oid add%- Console.rite?ine"Abstract class add"%2 /

/

hen e0ternal imlementation is done no !isibility secifer must be used likeublic(ri!ate etc.(

ethod add% o interace can be in!oked only using interace reerence( thiscannot be in!oked using instance o the class.

Another usage o e0licit interace imlementation is whene!er a class imlementsa number o interaces which contains same method names.

interace IAdd- !oid oerate%2 /interace Iub- !oid oerate%2 /

interace Iul- !oid oerate%2 /

class gm:IAdd(Iub(Iul-

!oid I!dd"oerate% - Console.rite?ine"ethod o IAdd"%2 / !oid I#$b.oerate% - Console.rite?ine"ethod o Iub"%2 / !oid I%$l"oerate% - Console.rite?ine"ethod o Iul"%2 /

/

class 10- ublic static !oid ain% - IAdd r2 Iub r52 Iul r2

&


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gm a = new gm%2

r = IAdd% a2 r.oerate%2

r = Iub% a2 r.oerate%2

r = Iul% a2

r.oerate%2 / /

$ilding interface hierarchies

imilar to a class ha!ing hierarchies interaces can also ha!e hierarchies. 7omostnterace defnes a general beha!iour( while the most deri!ed interace defnesmore secifc beha!iors.

10:interace IAdd

- !oid add%2 /interace Iub:IAdd- !oid sub%2 /interace Iul:Iub- !oid ul%2 /

class gm:Iul- !oid add% - Console.rite?ine"In add"%2 / !oid sub%

- Console.rite?ine"In sub"%2 / !oid mul% - Console.rite?ine"In mul"%2 //

class 10- ublic static !oid ain% -

gm a = new gm%2 Iul r = Iul% a2 r.add%2 r.sub%2 r.mul%2 //

'


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10amle deicts interace hierarchy. Class gm imlements each beha!iour in thenterace hierarchy2 since it deri!es rom the nth most interaces in hierarchy.ul has all the beha!iors o IAdd & Iub due to interace hierarchy

%$ltiple ase interfaces

nterace IAdd interace Iub interace Iul:IAdd(Iub-!oid add%2 / -!oid sub%2 / -!oid mul%2 /

class gm:Iul- !oid add% - Console.rite?ine"In add"%2 / !oid sub% - Console.rite?ine"In sub"%2 / !oid mul% - Console.rite?ine"In mul"%2 //

class 10-

ublic static !oid ain% - gm a = new gm%2 Iul r = Iul% a2 r.add%2 r.sub%2 r.mul%2 //

Convertible interface

nteraces are used e0tensi!ely throughout the .917 base class library2 one o thems ICon!ertible interace.

ain usage o this interace is to con!ert inormation rom one tye to anotherdynamically using interace based rogramming techniue.

Con!ertible interace is defned in .917 rame work as shown

ublic interace ICon!ertible-

7yeCode )et7yeCode%2bool 7o;oolean I*ormatro!ider ro!ider%2byte 7o;yte I*ormatro!ider ro!ider%2char 7oChar I*ormatro!ider ro!ider%2......uIntEF 7o


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All intrinsic data tyes o C# are aliases to structures resent in ystemnamesace. 1ach o these structures defnes within them many methods &mlements many interaces.

ublic struct ;oolean:IComarable( ICon!ertible-

...

.../

En$erable & IEn$erator interface

1numerable and I1numerator interace are used to iterate through a collection o custom tyes e0: array o class( structures%1numerable interace contain only one abstract member unction called

)et1numerator%. 7his method will return an Interace called I1numerator.

nterace I1numerable

- I1numerator )et1numerator%2 /

public IEnumerator GetEnumerator(){ //return IEnumerator of our Custom Type return(IEnumerator)this;}

1numerator is an interace which hels to iterate through any custom collectionhat is internal to a class.


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G 7he 8eset method resets the collection inde0 to its initial!alue o H5. 7his in!alidates the enumerator.

G 7he Current method returns the current ob$ect at ositionJ.

;oth I1numerable & I1numerator interaces are defned under ystem.Collectionsnamesaces.

10:using ystem2using ystem.Collections2class stud -

string name( usn2 ublic studarams stringJ a% - name = aKJ2 usn = a5J2 / ublic o!erride string 7otring% - return "9ame : " > name > "


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using ystem2 using ystem.Collections2class stud

-M./

class cstud : I1numerable(I1numerator

-

M

int os2

ublic cstud%- os = H52MM.

/

cstud a = new cstud%2

a.o!e9e0t%2Console.rite?ine a.Current %2a.8eset%2

oreachstud 0 in a%

Console.rite?ine0%2

a.o!e9e0t% are e0licit in!ocations o I1numerator methods. 1!en withoute0licit in!ocation using oreach loo all the elements will be read.

7o a!oid the imlementation o I1numerator methods( ollowing code must bewritten.

public bool MoveNext()

{ if (pos < a.Length-1)

{ pos++; return true; else

return false;

public voi! "eset() { pos # -1;

public ob$ect %urrent

{ get { return a&pos';

public nu*erator etnu*erator()

{ return (nu*erator)this;

11


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class stud+ public string name, usn; public stud(string n, string u)

+ name - n; usn - u; . public override string ToString()

+ return name / 0 0 / usn;..

stud p - ne stud(0aa0,0110);

stud - p;usn - 0220;"onsole4rite5ine(p);"onsole4rite5ine();

public IEnumerator GetEnumerator(){ return a.GetEnumerator(); }

Data member a is an array. ystem.Array already imlements I1numerator itNs notnecessary to imlement I1numerator methods once again.

Cloneable Interface

ntrod$ction

7he ystem.ICloneable interace defnes a method o cloning coying% to create anew ob$ect o a class with the identical !alue as an e0isting ob$ect. 7his interacedefnes a single method named Clone% as shown below.

public interface ICloneable

{

object Clone( );

}

7here are two ways to clone an ob$ect:

1 #hallow copy H ame data may be shared by both new & old ob$ect.

2 eep copy H ;oth new & old ob$ect will ha!e its own coy o data.

A shallow coy is the easiest way to clone an ob$ect. 7his can be achie!ed with theemberwiseClone% method inherited by all classes rom b$ect. @owe!er( this tyeo cloning is not eBecti!e.

12


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class stud :ICloneable

+ public string name, usn; public stud(string n, string u) + name - n; usn - u; . public override string ToString()

+ return name / 0 0 / usn;. public object Clone( )

{ return new stud(name,usn); }

.

stud p - ne stud(0aa0,0110);stud - (stud)p.Clone();usn - 0220;

"onsole4rite5ine(p);"onsole4rite5ine();

class stud :ICloneable

+ public string name, usn; public stud(string n, string u)

+ name - n; usn - u; . public override string ToString() + return name / 0 0 / usn;. public object Clone( )

{ return this.MemberwiseClone(); }

.

stud p - ne stud(0aa0,0110);

stud - (stud)p.Clone();

usn - 0220;"onsole4rite5ine(p);"onsole4rite5ine();

class addr +

public int hno; public addr(int h)

+ hno - h; . public override string ToString()

+ return hnoToString(); . .

class stud 6 $"loneable+public string name;

public addr r;

public stud(string n)

+ name - n; r = new addr(); .

public override string ToString() + return (name / 0 0 /r);. public ob7ect "lone()

+return this8emberise"lone(); ..

stud a - ne stud(0aa0);stud b - (stud)a"lone(); ;

b.r.hno = !!;

"onsole4rite5ine(a);

"onsole4rite5ine(b);

= 2 assignment results in two reerences to the same stud ob$ect on the hea2modifcations using either reerence aBect the same ob$ect on hea.

n order to ha!e a coy o in 2 a searate memory or has to be acuired and!alue o has to be coied into it. In order to imlement this( stud class mustmlement ICloneable interace as shown below.

Clone% method coy the !alues o dataHmembers o in!oking o$bect into a newob$ect and return it to the . 9ow .usn will ha!e !alue 55 and .usn will ha!e!alue .

7he abo!e rogram can be written as shown below.

emberwiseClone% is inherited by ob$ect and it is in!oked by this reerence.emberwiseClone% will do the same task as seen beore.

Elaborate Cloning

13


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class stud 6 $"loneable+ 9 9 public object Clon() {

stud temp = new stud();

temp.name = name;

temp.r = new addr(r.hno);

return temp;

}

.

This implements Deep cop:

Class stud contains a reerence to addr class.

As( each ob$ect o stud is created r acuires memory and then !alue will be lacednto it.

cloning shallow coy% is alied on ob$ect o tye stud using emberwiseClone%as shown abo!e( then b.r.hno and a.r.hno will be holding same data.

n other words b.r.hno and a.r.hno will be ointing to same memory. 7o a!oid this(emberwiseClone% will not be in!oked2 but e0licit code will be written tomlement dee coy.

the abo!e code is relaced then b.r.hno will be 5KK and a.r.hno will be 5.

#yste"ICoparable

ystem.IComarable interace secifes a beha!ior that allows an collection oob$ects to be sorted based on a secifed key.

interface IComparable{

int CompareTo(ob"ect o);}

7his interace is used to comare similar tye ob$ects on a secifed keyon datamember%.

Collection o inormation can be o tyes5% Collection o intrinsic tyes% Collection o user defned tyes

1#


15/21

class stud : IComparable+

string name;

int id;

public stud(string n,int i)

+ name - n; id - i; .

public override string ToString() + return(name / 0 0 / id); .

int IComparable.Compare"o(object o)

{

i# (id $ ((stud)o).id)

return ; i# (id % ((stud)o).id)

return &;

else

return !;

}

.

class pgm+

public static void ()

+

stud< a - ne stud3


16/21

*or a better e0lanation( add a Console.rite?ine% call inside yourcomare method and then call Array.ort. Rou'll see your method gets

called many times.J

Comare7o% is imlemented as Se0licit interace imlementationT.

#yste"ICoparer

7he role o ICoparer is to ro!ide additional comarison mechanisms.

As( shown in the e0amle collection SaT is sorted on id. I it has to be sorted onname also( then IComarer interace has to be imlemented. IComarer cannot bemlemented on the same class stud but must be imlemented by heler class orstud.).*:nterface IComparer { int Compare(ob"ect o&' ob"ect o); }

@eler class is one which imlements IComarer interace or class stud byecei!ing two !alues o tye stud. @eler class $ust contains one method i.e

Comare% method.

10:

class stud : IComparable

{

string name"

int id" public stud(string n,int i)

{ name = n" id = i" #

public override string 6o*tring()

{ return(name ' 2 2 ' id)" #

int IComparable.CompareTo(object o)

{

if (id > ((stud)o).id)

return 1;

if (id < ((stud)o).id)

return -1;

else return ;

!

#

1&


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nterfaces in #yste"Collections naespace

ystem.Collections defnes a number o interaces. ost o the classes defnedwithin ystem.Collections namesace imlement these interaces.

#yste"CollectionsInterface

%eaning

I1numerable 8eturn I1numerator interace or a gi!en ob$ect

$$78!P89 C!A**

class "elper : IComparer

{

int IComparer.Compare(object o1# object o$)

{

return strin%.Compare(

((stud)o1).ret#

((stud)o$).ret);

!

!

class pgm {

public static void Main() {

stud45 a = ne stud4/5"

a435 = ne stud(2bb2, )"

a4-5 = ne stud(2cc2, -)"

a45 = ne stud(2aa2, /)"

&oreac% (stud 1 in a)

Console.rite!ine(1)"

&rra'.ort(a);

Console.rite!ine(2nnn2)"



&rra'.ort(a# ne "elper());

Console.rite!ine(2nnn2)"

Console.rite!ine(2*orting on name2)"



Console.9ead()"#

#

1'


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$ash"ode>rovider

$"omparer

$?numerator

$Dictionar:?numerator

$?numerable

$"ollection

$5ist

$Dictionar:

I1numerable )enerally used to suort oreach style iteration o subtyes

IComarer Allows to ob$ects to be comaredI?ist ro!ides acility to add( remo!e( and inde0 items

in a list o ob$ectsIDictionary Allows an ob$ect to reresent its contents using

name3!alue airs.ICollection Defnes generic characteristics or a collection

class

any o these interaces are related by an interace hierarchy( others are standHalone entities.

Collection interface

7his interace ro!ides a small set o roerties that allows rogrammer todetermine.

a% number o items in the containerb% threadHsaety o the container

c% ability to coy contents into a ystem.Array

p$blic interface ICollection * IEn$erable+

,,IEn$erable eberint Co$nt +get- .bool Is#ynchroni/ed + get- .ob0ect #yncoot +get- .

void Copy(o!rray array int index)-.

ictionary interface

Dictionary is a collection o name & !alue airs.10 : tudent name and marks Car name and no.

Dictionary imlements all the unctionalities o ICollection & I1numerable.

1


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p$blic interface Iicitionary * ICollection IEn$erable+,,ICollection and IEn$erable ebersbool Isixed#i/e+ get- .bool Isead4nly + get- .5"void !ddob0ect key ob0ect val$e)-void Clear)-

5".

6ist interface

7his interace ro!ides the ability to insert( remo!e and inde0 items into acontainer

ublic interace I?ist : ICollection( I1numerable-

M..

!oid Clear%2!oid Insertob$ect !alue%2!oid Insertint inde0( ob$ect !alue%2!oid 8emo!eob$ect !alue%2!oid 8emo!eint inde0%2M../

Classes in #yste"Collections naespace

#yste"CollectionsClass

%eaning Interfaces ipleented bythe class

Array?ist Dynamically siOed arrayo ob$ects.

I?ist( ICollection( I1numerable &ICloneable

Queue *I* ueue ICollection(ICloneable &I1numerable

tack ?I* ueue ro!idingush( o & eek

unctionality

ICollection & I1numerable

orted?ist imilar to dictionary IDictionary( ICollection(I1numerable & ICloneable

7orking with !rray6ist (ype

As the name Array?ist is used to store a collection o similar tyes o ntrinsic3standard tye. e!eral methods are suorted within this class to insert(delete & modiy the inormation stored within the collection.10: Array?ist cmA?ist = new Array?ist%2

1


20/21

cmA?ist.Add8angenew cmJ - new cm5(%( new cmL(F%/%2

Console.rite?ineS9o o cms -K/S(cmA?ist.Count%2

oreachcm c in cmA?ist%- Console.rite?inec.rint%%2 /

cmA?ist.Insert(new cm5K(K%%2

Console.rite?ineS9o o cms -K/S(cmA?ist.Count%2

Add8ange% method o Array?ist is used to oulate Array?ist with a set o comle0 tyes2 which is basically a shorthand notation or calling Add% method nnumber o times.9umber o inormations in the collection is obtained by Count roerty. Insertallows to ut an inormation into the Array?ist at a secifed inde0.

7rking with 8$e$e (ype

Queues are containers into which items are accessed using frstHin( frstHout basis.

%ebers of #yste"Collection"8$e$e

%ening

Deueue% 8emo!es & returns the ob$ect atthe beginning o the ueue

1nueue% Adds an ob$ect to the end o theueue

eek% 8eturns the ob$ect at thebeginning o the ueue withoutremo!ing it.

10:

Queue cmQ = new Queue%2

cmQ.1nueuenew cm5( %%2cmQ.1nueuenew cmL( F%%2cmQ.1nueuenew cmU( E%%2

Console.rite?ine"Queue siOe -K/"( cmQ.Count%2

cm%cmQ.eek%%%.rint%2

cm%cmQ.Deueue%%%.rint%2cm%cmQ.Deueue%%%.rint/2

tems are insereted into the ueue using the method 1nueue%. eek% methodallows to !iew the frst item currently in the ueue.

2*


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Deueue% remo!es the item rom the ueue. eek% and Dueue% methods areha!ing the return tye as ob$ect( which is o tye generic. 1nueue% method isha!ing a arameter which is o tye generic3ob$ect.

7orking with #tack (ype

tack maintains inormation using a lastHin( frstHout basis. tack defnes amember named ush% & o% to lace an item onto & remo!e items rom thestack. eek% method used to !iew the frst element on the stack.

10:

tack cmQ = new tack%2

cmQ.ushnew cm5( %%2cmQ.ushnew cmL( F%%2cmQ.ushnew cmU( E%%2Console.rite?ine"Queue siOe -K/"( cmQ.Count%2

cm%cmQ.eek%%%.rint%2

cm%cmQ.o%%%.rint%2cm%cmQ.o%%%.rint%2

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Interface and Collections

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