Collections concept in Java

8/21/2019 Collections concept in Java

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Collection

List Set

SortedSet

1D Collection FrameWork Interfaces


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Methods in java.util.Collection•public int sie!"•public boolean is#mpt$!"•public boolean add!%bject"

- used to add elements to any CFW variable only at the end.- Returns TRUE -> when Collection and List interfaces are used.- Returns False -> when et and ortedet interfaces are used if

du!licate elements are entered.•&ublic boolean add'll!Collection"

- "ddin# the contents of one CFW variable to another $which is referred as "da!tability- one of the advanta#esof CFW%.•&ublic %bject() to'rra$!" - Used for convertin# all the elements of CFW in the form of array

ob&ect of &ava.lan#.ob&ect.


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et o s n ava.ut . st•&ublic void add!int*%bject"

-Used for addin# an element to any CFW variable either inbe#inini#'end'middle.

#+ample, -(nsertin# element at the end of the list

l.add$l.si)e$%*new (nte#er$+,,%%•public %bject et!int"

- used to obtain a value from the CFW variable by !assin# the!osition.

#+ample,b&ect ob&/l.#et$0%ystem.out.!rintln$ob&%

/%0#, If the position entered is ron then 2null3 isreturned.•

public %bject remove!int"•public void remove!%bject"

-Used to remove the values for a CFW variable based on positionor content.

-If removal is based on content onl$ the 4rst occurance is

removed.•&ublic void remove'll!"


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Methods in java.util.Set

• "s et is the derived from thecollection interface* it inherits all themethods of collection.

• E1ce!t the basic di2erence i.eUni3ue elements are allowed and theelements are dis!layed in random

order.


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5ava.util.SortedSet• ame as et interface but the elements

are dis!layed in sorted order.• 4ublic b&ect 5rst$%

• 4ublic b&ect last$%

• 4ublic ortedet headet$b&ect ob&%

• 4ublic ortedet subet$b&ect ob&+*

b&ect ob&0%

• 4ublic ortedet tailet$b&ect ob&%

0aret%bject

6i78obj

0aret%bject

6i 9ob

%bj178 6i7

%bj:

6i represents value of

SortedSet


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E6"74LE

1;

:;

;

?;

@;

A;

B;

Sorted Set hs8ss.headSet!ne Inteer!


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e standard Collection classes


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0he 'rra$List Class

The"rrayListclass e1tends"bstractListand im!lementstheListinterface."rrayListis a

#eneric class that has this declaration8

class 'rra$List7#9

9ere*Es!eci5es the ty!e of ob&ects that the list will hold.


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im!ort &ava.util.:class 'rra$ListDemo ;!ublic static void main$trin# ar#s$%

ystem.out.!rintln$?(nitial si)e of al8 ? @ al.si)e$%%'' "dd elements to the array list.al.add$?C?%al.add$?"?%al.add$?E?%al.add$?A?%al.add$?B?%al.add$?F?%al.add$+* ?"0?%ystem.out.!rintln$?i)e of al after additions8 ? @ al.si)e$%%'' Bis!lay the array list.ystem.out.!rintln$?Contents of al8 ? @ al%'' Remove elements from the array list.al.remove$?F?%al.remove$0%ystem.out.!rintln$?i)e of al after deletions8 ? @al.si)e$%%

ystem.out.!rintln$?Contents of al8 ?@ al%

0he output from this proram isshon here,(nitial si)e of al8 ,i)e of al after additions8 D

Contents of al8


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%btainin an 'rra$ from an 'rra$List

When worin# with "rrayList* you will sometimes want to obtain an actualarray that containsthe contents of the list. Gou can do this by callin# to"rray$ %* which is de5ned

by Collection.everal reasons e1ist why you mi#ht want to convert a collection into anarray* such as8H 0o obtain faster processin times for certain operations 0o pass an arra$ to a method that is not overloaded to accept acollection

0o interate collection-based code ith leac$ code that does notunderstand collections

%bject( ) to'rra$! "709 0( ) to'rra$!0 arra$( )"


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Convert an 'rra$List into an arra$.im!ort &ava.util.:class "rrayListTo"rray ;!ublic static void main$trin# ar#s'' "dd elements to the array list.al.add$+%al.add$0%al.add$I%al.add$J%

ystem.out.!rintln$?Contents of al8 ? @ al%'' Ket the array.(nte#er ia


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0he LinkedList Class

TheLinedListclass e1tends"bstracte3uentialListand im!lementstheList*Be3ue* andueueinterfaces.

(t !rovides a lined-list data structure.LinedListis a #eneric class that

has this declaration8

class LinkedList7#9


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im!ort &ava.util.:class LinkedListDemo ;!ublic static void main$trin# ar#s ll / new LinedListtrin#>$%

'' "dd elements to the lined list.ll.add$?F?%ll.add$?A?%ll.add$?B?%ll.add$?E?%ll.add$?C?%

ll.addLast$?M?%ll.addFirst$?"?%ll.add$+* ?"0?%ystem.out.!rintln$?ri#inal contents of ll8 ? @ ll%'' Remove elements from the lined list.ll.remove$?F?%

ll.remove$0%ystem.out.!rintln$?Contents of ll after deletion8 N@ ll%'' Remove 5rst and last elements.ll.removeFirst$%ll.removeLast$%ystem.out.!rintln$?ll after deletin# 5rst and last8 N@ ll%

'' Ket and set a value.

trin# val / ll.#et$0%ll.set$0* val @ ? Chan#ed?%ystem.out.!rintln$?ll afterchan#e8 ? @ll%

0he output from this proram isshon here,ri#inal contents of ll8


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0he GashSet Class9ashete1tends"bstractetand im!lements theetinterface. (t creates acollection thatuses a hash table for stora#e.9ashetis a #eneric class that has thisdeclaration8

class GashSet7#9

9ere*Es!eci5es the ty!e of ob&ects that the set will hold.

LinkedGashSet

(t maintains a lined list of the entries in the set* in the order in whichthey were inserted.class LinkedGashSet7#9

0he 0reeSet Class

Treeete1tends"bstractetand im!lements theOavi#ableetinterface. (tcreates acollection that uses a tree for stora#e. b&ects are stored in sorted*ascendin# order.

class 0reeSet7#9


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Demonstrate GashSet.im!ort &ava.util.:class 9ashetBemo ;!ublic static void main$trin# ar#s hs / new 9ashettrin#>$%'' "dd elements to the hash set.hs.add$?A?%hs.add$?"?%hs.add$?B?%

hs.add$?E?%hs.add$?C?%hs.add$?F?%ystem.out.!rintln$hs%

0he folloin is the output from thisproram,class GashSet7#9(D* '* F* C* H* #)

class LinkedGashSet7#9(H* '* D* #* C* F)hich is the order in hich the elementsere inserted.class 0reeSet7#9('* H* C* D* #* F)


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(terator (nterface• (f we want to dis!lay each element of the

Collection* we can use one of these two!rocedures8

• ne way to do this is to em!loy aniterator*which is an ob&ect that im!lementseither the Iterator or

the ListIterator interface.

• Iterator enables you to cycle throu#h a

collection* obtainin# or removin#elements.

• ListIterator e1tends Iterator to allowbidirectional traversal of a list* and themodi5cation of elements.


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7ethods de5ned by (terator


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7ethods de5ned byList(terator


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E1am!le of (terator

(terator itr/c.iterator$%While$itr.hasOe1t$%% Forward

Birection

; itrb&ect ob&/itr.ne1t$%

(nte#er io/$(nte#er%ob&

int 1/io.intPalue$% ystem.out.!rintln$1%

+,

0, I, J,


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E1am!le of List(teratorList(terator litr/l.List(terator$%

while$litr.hasOe1t$%% ;

b&ect ob&/litr.ne1t$% ystem.out.!rintln$ob&%

while$litr.has4revious$%%;

b&ect ob&/litr.!revious$%

(nte#er io/$(nte#er%ob&

(nt n/io.intPalue$%

ystem.out.!rintln$ob&%

'' Bemonstrate iterators


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'' Bemonstrate iterators.im!ort &ava.util.:class (teratorBemo ;!ublic static void main$trin# ar#s$%'' "dd elements to the array list.al.add$?C?%al.add$?"?%al.add$?E?%al.add$?A?%

al.add$?B?%al.add$?F?%'' Use iterator to dis!lay contents of al.ystem.out.!rint$?ri#inal contents of al8 ?%(teratortrin#> itr / al.iterator$%while$itr.hasOe1t$%% ;

trin# element / itr.ne1t$%ystem.out.!rint$element @ ? ?%ystem.out.!rintln$%'' 7odify ob&ects bein# iterated.List(teratortrin#> litr / al.list(terator$%

while$litr.hasOe1t$%% ;trin element / litr.ne1t

litr.set$element @ ?@?%ystem.out.!rint$?7odi5ed contentsof al8 ?%itr / al.iterator$%

while$itr.hasOe1t$%% ;trin# element / itr.ne1t$%ystem.out.!rint$element @ ? ?%ystem.out.!rintln$%'' Oow* dis!lay the list bacwards.ystem.out.!rint$?7odi5ed listbacwards8 ?%while$litr.has4revious$%% ;trin# element / litr.!revious$%ystem.out.!rint$element @ ? ?%

ystem.out.!rintln$%0he output is shon here,

%riinal contents of al, C ' # H D FModi4ed contents of al, C ' #H D F

Modi4ed list backards, F D H


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0B Collection Framewor

7"4

• The 9ash7a! Class

• The 9ash7a! class e1tends "bstract7a! andim!lements the 7a! interface. (t uses a hash

table to store the ma!.

This allows the e1ecution time of #et$ %and !ut$ %to remain constant even for lar#e sets.

9ash7a! is a #eneric class that has thisdeclaration8

• class 9ash7a!Q* P>

• 9ere*Q s!eci5es the ty!e of eys* and P s!eci5esthe ty!e of values.


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7"4 (OTERF"CE

• ava.util.7a!

• ava.util.7a!.Entry

•

ava.util.orted7a!

im!ort &ava util :


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im!ort &ava.util.:class GashMapBemo ;!ublic static void main$trin# ar#s hm / new 9ash7a!trin#* Bouble>$%

'' 4ut elements to the ma!hm.!ut$?ohn Boe?* new Bouble$IJIJ.IJ%%hm.!ut$?Tom mith?* new Bouble$+0I.00%%hm.!ut$?ane Aaer?* new Bouble$+IDS.,,%%hm.!ut$?Tod 9all?* new Bouble$.00%%hm.!ut$?Ral!h mith?* new Bouble$-+.,S%%

'' Ket a set of the entries.et7a!.Entrytrin#* Bouble>> set / hm.entryet$%'' Bis!lay the set.for$7a!.Entrytrin#* Bouble> me 8 set% ;ystem.out.!rint$me.#etQey$% @ ?8 ?%ystem.out.!rintln$me.#etPalue$%%

ystem.out.!rintln$%'' Be!osit +,,, into ohn Boes account.double balance / hm.#et$?ohn Boe?%hm.!ut$?ohn Boe?* balance @ +,,,%ystem.out.!rintln$?ohn Boes new balance8 ? @

hm.#et$?ohn Boe?%%

%utput from this proram isshon here !the precise orderma$ var$",Ral!h mith8 -+.,S

Tom mith8 +0I.00 ohn Boe8 IJIJ.IJ Tod 9all8 .00 ane Aaer8 +IDS., ohn BoeVs new balance8 JJIJ.IJ


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ava.util.7a!

• !ublic int si)e$%

• !ublic boolean isEm!ty$%

•

!ublic boolean !ut$b&ect eyob&*b&ect vob&%

E#8 m.!ut$new (nte#er$+,%* newFloat$0.f%%

• !ublic b&ect #et$b&ect ob&%


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ava.util.7a!.Entry

• !ublic b&ect #etQey$%

• !ublic b&ect #etPalue$%


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ava.util.orted7a!

• !ublic b&ect 5rst$%

• !ublic b&ect last$%

•

!ublic orted7a! head7a!$b&ectob&%

• !ublic orted7a! sub7a!$b&ectQob&+* b&ect Pob&+%

• !ublic orted7a! tail7a!$b&ectob&%

Collections concept in Java

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