Linkedlist in Java

8/19/2019 Linkedlist in Java

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TCSS 342, Winter 2005

Lecture Notes

Linked List Implementation

Weiss Ch !, pp 1"3#205

Weiss Ch 1$, pp 53$#54"


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Collections

collection% an o&'ect that stores data inside it(aka a )data structure) the o&'ects stored are called elements some maintain an orderin*, some don+t some collections allo duplicates, some don+t an arra- is like a .er- crude )collection) t-pical operations% add element, remo.e element,

clear all elements, contains or /nd element, *et

sie most collections are &uilt ith particular kinds o

data, or particular operations on that data, inmind

eamples% java.util.ArrayList, java.util.HashMap,java.util.TreeSet


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a.a+s Collection interace

a.a pro.ides an interace java.util.Collection to represent man- kinds o collections It has theolloin* methods%

public boolean add(Object o)

ppends the speci/ed element to this collection

public void clear()

emo.es all o the elements o this collection

public boolean contains(Object o)eturns true i this collection contains the speci/ed element

public boolean containsAll(Collection coll)

eturns true i this collection contains all o the elements in

the speci/ed collection


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Collection interace,cont+d

public boolean isEpty()eturns true i this list contains no elements

public !terator iterator()

eturns a special o&'ect or eaminin* the elements o the

list in order 6seen later7

public boolean reove(Object o)

emo.es the /rst occurrence in this list o the speci/edelement

public int si"e()

eturns the num&er o elements in this list

public Object#$ toArray()

eturns an arra- containin* all o the elements rom this list


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n eample collection% List

list% an ordered se8uence o elements,each accessi&le &- a 0#&ased inde one o the most &asic collections


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List eatures

ORDERING% maintains order elements ereadded6ne elements are added to the end &- deault7

DUPLICATES% -es 6alloed7 OPERATIONS% add element to end o list, insert

element at *i.en inde, clear all elements,search or element, *et element at *i.en inde,

remo.e element at *i.en inde, *et sie some o these operations are ine9cient: 6seen later7

list mana*es its on sie( user o the list doesnot need to orr- a&out o.er/llin* it


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a.a+s List interace

a.a also has an interace java.util.List to represent a list o o&'ects It adds theolloin* methods to those in Collection%6a partial list7

public void add(int inde%& Object o)

Inserts the speci/ed element at the speci/ed position inthis list

public Object 'et(int inde%)eturns the element at the speci/ed position in this list

public int inde%O(Object o)

eturns the inde in this list o the /rst occurrence o thespeci/ed element, or * i the list does not contain it


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List interace, cont+d

public int last!nde%O(Object o)

eturns the inde in this list o the last occurrence o thespeci/ed element, or #1 i the list does not contain it

public Object reove(int inde%)

emo.es the o&'ect at the speci/ed position in this list

public Object set(int inde%& Object o)

eplaces the element at the speci/ed position in this listith the speci/ed element

Notice that the methods added to Collection &- List all deal ith indees( a list has indeeshile a *eneral collection ma- not


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Some list 8uestions

all o the list operations on the pre.ious slidecould &e perormed usin* an arra- instead:

open 8uestion% What are some reasons h-e mi*ht ant to use a list class, rather thanan arra-, to store our data;

thou*ht 8uestion%


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rra- list

array list% a list implemented usin* anarra- to store the elements encapsulates arra- and = o elements 6sie7 in a.a% java.util.ArrayList hen -ou ant to use ArrayList, remem&er

to iport java.util.+,


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ArrayList eatures

think o it as an auto#resiin* arra- that canhold an- t-pe o o&'ect, ith man-con.enient methods

maintains most o the &ene/ts o arra-s,such as ast random access

rees us rom some tedious operations onarra-s, such as slidin* elements andresiin*

can call toStrin' on an ArrayList to printits elements #*& -./& Marty Stepp& Hello$


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Collections class

Class java.util.Collections has man- utilit-methods that do useul thin*s to collections

public static void copy(List dest& List src)

public static void ill(List list& Object value)public static Object a%(Collection coll)

public static Object in(Collection coll)

public static void reverse(List list)

public static void shule(List list)public static void sort(List list)

public static void s0ap(List list& int i& int j)

>ample%Collections.sort(yArrayList),


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?pen 8uestions

ased on the precedin* anal-sis, hen isan ArrayList a *ood collection to use;When is it a poor perormer;

Is there a a- that e could / some othe pro&lems ith the ArrayList;

Should e represent our list in a diDerenta-;


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some ArrayList pro&lems

an insertion into a ull list causes a lar*ereallocation

an insertion to the ront )slides) don the

su&se8uent items 6slo:7 a remo.al also )slides) don su&se8uent

items

still need to use indeesEsu&scripts a lot somehat u*l- s-nta to use it


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The underl-in* issue

the elements o an ArrayList are tooti*htl- attached( can+t easil- rearran*ethem

can e &reak the element stora*e apartinto a more d-namic and Fei&lestructure;


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Nodes% o&'ects to storeelements

let+s make a special )node) t-pe o o&'ectthat represents a stora*e slot to hold oneelement o a list

each node ill keep a reerence to thenode ater it 6the )net) node7

the last node ill ha.e ne%t 11 null

6dran as E 7, si*ni-in* the end o the list


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Node implementation

2+ Stores one eleent o a lin3ed list. +2public class 4ode 5

public Object element, public 4ode next,

public 4ode(Object eleent) 5

this(eleent& null),

6

public 4ode(Object eleent& 4ode ne%t) 5

this.eleent 1 eleent,

this.ne%t 1 ne%t,

6

6


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Linked node pro&lems 6a7

Let+s eamine sample chains o nodesto*ether, and tr- to rite the correctcode or each

each Node stores an !nte'er o&'ect

1

&eore%

ater%


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Linked node pro&lems 6&7

2 &eore%

ater%

3

&eore%

ater%


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Linked node pro&lems 6c7

4 &eore%

ater%

5

&eore%

ater%


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Linked node pro&lems 6d7

! &eore%

ater%

$

&eore%

ater%


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Linked list

linked list% a list implemented usin* alinked se8uence o nodes the list onl- needs to keep a reerence to the

/rst node 6e mi*ht name it y7ront7 in a.a% java.util.Lin3edList

6&ut e+ll rite our on7


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Linked list implementation

2+ Models an entire lin3ed list. +2public class MyLin3edList 5

private 4ode y7ront,

public MyLin3edList() 5

y7ront 1 null,

6

2+ Methods go here +2

6


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Let+s dra them to*ether

an add operation at the ront, &ack, and middle

a remo.e operation

a *et operation a set operation

an inde o 6searchin*7 operation


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nal-sis o Lin3edList runtime

?@>TI?Nadd to start o listadd to end o listadd at *i.en inde

clear*et/nd inde o an o&'ectremo.e /rst element

remo.e last elementremo.e at *i.en indesetsie

toStrin*

ANTIB> 6i*#?h7 ?617 O(n) O(n)

?617 O(n) O(n) ?617

O(n) O(n) O(n) O(n)

O(n)


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n optimiation% ySi"e

pro&lem% arra- list has a ?617 si"e method, &ut the linked list needs ?6n7time

solution% add a ySi"e /eld to our linkedlist hat chan*es must &e made to the

implementation o the methods o the linkedlist;


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.ariation% dumm-header

dmmy !eader% a ront nodeintentionall- let &lank y7ront ala-s reers to dumm- header

6y7ront

ill ne.er &enull

7 re8uires minor modi/cation to man- methods

surprisin*l-, makes implementation mucheasier


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Gou&l-#linked lists

add a prev pointer to our 4ode class allos &ackard iteration 6orList!terator7

some methods need to &e modi/ed hen addin* or remo.in* a node, e must /

the prev and ne%t pointers to ha.e the

correct .alue: can make it easier to implement some

methods such as reove


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Com&inin* the approaches

Bost actual linked list implementationsare dou&l-#linked and use a dumm-header and dmmy tail

this actuall- makes a .er- cleanimplementation or all linked list methodsand pro.ides *ood e9cienc- or as man-

operations as possi&le


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Impro.ed Lin3edList runtime

?@>TI?Nadd to start o listadd to end o listadd at *i.en inde

clear*et/nd inde o an o&'ectremo.e /rst element

remo.e last elementremo.e at *i.en indesetsie

toStrin*

ANTIB> 6i*#?h7 ?617 ?617 O(n)

?617 O(n) O(n) ?617

?617 O(n) O(n) ?617

O(n)


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particularl- slo idiom

22 print every eleent o lin3ed listor (int i 1 9, i : list.size(), i;;) 5

Object eleent 1 list.get(i),

Syste.out.println(i ;


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The pro&lem o position

The code on the pre.ious slide is asteul&ecause it thros aa- the position each time e.er- call to 'et has to re#tra.erse the list:

it ould &e much &etter i e could somehokeep the list in place at each inde as elooped throu*h it

a.a uses special o&'ects to represent aposition o a collection as it+s &ein*eamined

these o&'ects are called )iterators)


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Iterators in a.a

interace java.util.!terator public boolean has4e%t()

eturns true i there are more elements tosee

public Object ne%t()eturns the net o&'ectin this collection, thenad.ances the iterator(thros an eception

i no more elementsremain

public void reove()Geletes the element that as

last returned &- ne%t 6not ala-s supported7


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Iterators on arra- lists

n iterator on an arra- list is simple( itmaintains an inde o its current node

iterators are not as useul on arra- lists Wh-;

What is the i*#?h o *et and set;

What is the i*#?h o add and remo.e; Goes the arra- list iterator impro.e this;


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Iterators on linked lists

an iterator on a linked list maintains 6atleast7 its current inde and a reerence tothat node

hen iterator() is called on a linked list,the iterator initiall- reers to the /rstnode 6inde 07


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Hiin* the slo LL idiom

22 print every eleent o the listor (int i 1 9, i : list.size(), i;;) 5

Object eleent 1 list.get(i),

Syste.out.println(i ;


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Iterator usa*e eample

MyLin3edList naes 1 ne0 MyLin3edList(),22 ... ill the list 0ith soe data ...

22 print every nae in the list& in upper case

Iterator itr = myList.iterator();0hile (

itr.hasNext()) 5

Strin' eleent 1 (Strin')itr.next(), Syste.out.println(eleent.to>pperCase()),6

22 reove strin's ro list that start 0ith


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ene/ts o iterators

speed up loops o.er linked lists+ elements What is the i*#?h o each iterator method;

pro.ide a uni/ed a- to eamine all

elements o a collection e.er- collection in a.a has an iterator method

in act, that+s the only *uaranteed a- to eaminethe elements o an- Collection 6see Slide 47

don+t need to look up diDerent collections+method names to see ho to eamine theirelements

don+t ha.e to use indees as much on lists


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Iterator is still not perect

22 print oddvalued eleents& 0ith their inde%es!terator itr 1 list.iterator(),

or (int i = 0; itr.has4e%t(), i;;) 5

int eleent 1 ((!nte'er)itr.ne%t()).int@alue(),

i (eleent - 11 *) Syste.out.println(i ;


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Bore iterator pro&lems

22 add a 9 ater any odd eleent

!terator itr 1 list.iterator(),

int i 1 9,

0hile (itr.has4e%t()) 5


i (eleent - 11 *) list.add(i, new Integer(0)); // ails

6

can+t use the iterator to add, set element .alues6iterator is pro*rammed to crash i list is modi/ed7

the iterator speeds up 'et and reove loops onl- the iterator reall- should &e a&le to help us speed

up loops that add elements or set elements+ .alues:


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List!terator interace

a.a interace java.util.List!terator etends!terator to add these methods% public void add(Object o)

public int ne%t!nde%()

public int previous!nde%()

public void set(Object o)

List!terator is also a&le to iterate in re.erse% public boolean hasBrevious()

public Object previous()

*et a List!terator &- callin* these methods on theList% 6&oth ArrayList and Lin3edList ha.e them7 public List!terator list!terator()

!"#li$ ListIterator listIterator(int index)


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List!terator usa*e

22 print oddvalued eleents& 0ith their inde%es

or (ListIterator itr = list.listIterator();

itr.hasNext(); ) 5


i (eleent - 11 *)

Syste.out.println(itr.!revio"sIndex() ;


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List!terator &ene/ts

usin* the List!terator internall- toimplement the methods o the linked listcan make the code cleaner and simpler%

public Object 'et(int inde%) 5

ListIterator itr = listIterator(index);

ret"rn itr.next();

6

should the code check the inde or

.alidit-;


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Summar-

lists are ordered, inte*er#indeedcollections that allo duplicates

lists are *ood or storin* elements in ordero insertion and tra.ersin* them in thatorder

linked lists are aster or add E remo.eoperations at the ront and &ack, &ut sloer

than arra- lists or ar&itrar- *et E setoperations

lists are &ad or searchin* or elements and

Linkedlist in Java

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