Java linked list - cs.bgu.ac.ilipc131/wiki.files/Class_Java_9.pdf · collection of objects (nodes) which both carry the data we want to store and a reference to the next node in the

Java linked list ▪ Often in programming we are required to systematically store some type of

information. A prime example of this is to use arrays, but when you don’t know

the amount of information to be stored we need a dynamic data structure.

▪ One option for us is to use a linked list. A linked list works by creating a

collection of objects (nodes) which both carry the data we want to store and a

reference to the next node in the list.

▪ There is more than one type of a linked list. Some different type of

linked list are shown below:

1. Singly linked list.

Root node links one way through all the nodes.

Last node links to NULL.

2. Doubly linked list.

Every nodes stores a reference to its previous node as well as its

next. Last node links to NULL.

1

Java linked list, cont. 3. Circular linked list.

Circular linked list have a reference to one node which is the tail

node and all the nodes are linked together in one direction forming a

circle.

▪ A singly linked list is a linear data structure where each element (node) is

a separate object.

Tail

Node< T >

data nextNode

Field nextNode references a Node< T > object, an object of the same <T> class .

Field data references the object of the <T> class . 2

Class List - definitions

• Class List represents a singly linked list.

• Each element (we will call it a node) of a list is comprising of

two items - the data and a reference to the next node.

• The last node has a reference to null. The entry point into a

linked list is called the head of the list. It should be noted that

head is not a separate node, but the reference to the first node.

If the list is empty then the head is a null reference.

• The number of nodes in a list is not fixed and can grow and shrink on

demand.

• In Java we are allowed to define a class (say, B) inside of another

class (say, A). The class A is called the outer class, and the class B is

called the inner class. The purpose of inner classes is purely to be

used internally as helper classes.

• The List class is the outer class and the Node class is the inner

class.

3

Class List - methods N Method’s name Method’s description

1 List() Constructor builds an empty linked list .

2 boolean isEmpty() Returns true if this list is empty and

false otherwise.

3 Node<T> getFirst() Returns the reference to first element in

this list. If list is empty returns null.

4 Node<T> insert(Node<T>

pos, T x)

Inserts the type T element x after the

specified position pos in this list and

returns the reference to inserted

element x.

5 Node<t> remove(Node<T>

pos)

Removes the first occurrence of the

specified element pos in this list and

returns the next element position.

We assume that pos != null.

6 String to String() Returns the string representation of

linked list. 4

Outer class List - UML diagram

List<T>

Node<T> first

List()

boolean isEmpty()

Node<T> getFirst()

Node<T> insert(Node<T> pos, T x)

Node<T> remove(Node<T> pos)

String toString()

Class name

Class variable

Class methods

Constructor

5

Inner class Node - UML diagram

Node<T>

private T data

private Node<T> nextNode

Node(T x)

Node( T data, Node<T> nextNode )

T getData()

Node<T> getNext()

Void setData( T data)

Void setNext(Node<T> nextNode)

String toString()

Constructors

Class variables

Class methods

Class name

6

Class List - implementation public class List<T>

{

private Node<T> first; // class List attribute

public List() {

this.first = null;

} // constructor

public Node<T> getFirst() {

return this.first;

}

public boolen isEmpty() {

return this.first == null;

} // isEmpty

public String toString() {

String str=“ [ “;

Node<T> pos=this.first;

while(pos != null) {

str=str + pos.getData(); // class Node<T> method

if(pos.getNext() != null)

str=str + ”, ”;

pos=pos.getNext();

} //while

str = str + “]”;

return str;

} // toString

7

Class List – implementation,cont. public Node<T> insert(Node<T> pos, T x) {

Node<T> q = new Node<T>(x); // creating new node

if( pos == null ) {

q.setNext(this.first);

this.first = q; // first element in the list

}

else {

q.setNext(pos.getNext());

pos.setNext(q);

} // else

return q;

} // insert

public Node<T> remove(Node<T> pos) {

if( this.first == pos ) {

this.first=pos.getNext(); // remove first node

return this.first;

}

else {

Node<T> prev = this.first;

while(prev.getNext() != pos) // searching pos reference

prev=prev.getNext();

prev.setNext(pos.getNext());

return prev.getNext();

} // else

} // remove

} // class List

Note: Class Node<T>

methods

8

Class List - test This program reads the names of 10 students ,builds linked list and prints the names which begins with an ‘A’ character.

public static void main(String args[ ]) { List<String> studNames = new List<String>(); Node<String> last = null; for(int i=0; i<10; i++) { System.out.println(“ Enter student name “); String name= reader.next(); last=studNames.insert(last,name); } // for Node<String> p =studNames.getFirst(); while(p != null ) { if( p.getData().charAt(0) == ‘A’) System.out.println(p.getData()); p=p.getNext(); } //while } // main 9

Class List – using external methods public static void nameA(Node<String> p)

{

while(p != null ) {

if( p.getData().charAt(0) == 'A') // getData from Node, charAt() from String

System.out.println(p.getData());

p=p.getNext();

} // while

} // nameA

public static void main(String args[ ])

{

List<String> studNames = new List<String>();

Node<String> last = null;

for(int i=0; i<10; i++) {

System.out.println(“ Enter student name “);

String name= reader.next();

last=studNames.insert(last,name);

} // for

Node<String> pl =studNames.getFirst();

nameA(pl); // calling method nameA from main

} // main

10

External methods – “what is” questions

11

1. What is the output for the next program giving the following linked list?

public static void what(List<Integer> list) { Node<Integer> a = list.getFirst(); Node<Integer> b = list.getFirst(); while (b !=null ) { Node<Integer> temp = a; a = a.getNext(); b = b.getNext(); list.remove(temp); if (b !=null) b = b.getNext(); } // while } //what

2. What is the purpose of the “what” method ?

public static void main(String[ ] args) {

List<Integer> ls = new List<Integer>();

Node<Integer> last=null;

System.out.print(" enter an integer -> ");

int x=reader.nextInt();

while ( x!=777) {

last= ls.insert(last, x);


x=reader.nextInt();

} // while

System.out.println(ls);

what(ls); // calling what method


} //main

“what is” questions - solution

12

enter an integer -> 1





[ 1, 2, 3, 4 ]

[ 3, 4 ]

Linked list values

sentinel

List before calling what

List after calling what

The what method

removes the first half

giving in the linked list.

output

Class List methods - example1 This program reads the coordinates of 10 points, builds linked list of Point type

and prints the coordinates of points which their value sums up to 20.


{

List<Point> ls =new List<Point>();

Node<Point> last = null;

for( int i=0; i<10; i++)

{

System.out.print(" enter X-> ");


System.out.print(" enter Y-> ");

int y=reader.nextInt();

last= ls.insert( last, new Point(x,y) );

} // for


printP20(ls); // calling external method (next slide) } // main

Building Point type linked list

Creating Point type linked list

13

Class List - method printP20

public static void printP20(List<Point> lst)

{

Node<Point> pos=lst.getFirst();

while(pos != null ) {

Point point=pos.getData();

if( point.getX()+ point.getY() <= 20)

System.out.println(point);

pos=pos.getNext();

} //while

} //printP20 Class Node method

Class Point methods

Class List method

14

method main - what’s different?


{


for( int i=0; i<N; i++)

{





ls.insert( null, new Point(x,y) );

} // for


printP20(ls); // calling external method

} // main


{


Node<Point> last = null;

for( int i=0; i<N; i++)

{





last= ls.insert( last, new Point(x,y) );

} // for


printP20(ls); // calling external method

} // main

15

method main output,N = 3 enter X-> 1 enter Y-> 2 enter X-> 3 enter Y-> 4 enter X-> 5 enter Y-> 6 [ x= 1.0 y= 2.0, x= 3.0 y= 4.0, x= 5.0 y= 6.0] x= 1.0 y= 2.0 x= 3.0 y= 4.0 x= 5.0 y= 6.0 enter X-> 1

enter Y-> 2 enter X-> 3 enter Y-> 4 enter X-> 5 enter Y-> 6 [ x= 5.0 y= 6.0, x= 3.0 y= 4.0, x= 1.0 y= 2.0] x= 5.0 y= 6.0 x= 3.0 y= 4.0 x= 1.0 y= 2.0

public Node<T> insert(Node<T> pos, T x) {

Node<T> q = new Node<T>(x);

if( pos == null ) {

q.setNext(this.first);

this.first = q; // first element in the list

} // if

else {

q.setNext(pos.getNext());

pos.setNext(q);

} // else

return q;

} // insert

16

This method checks if the linked list of String type is sorted .

public static boolean isSorted(List<String> lst)

{

Node<String> pos = lst.getFirst();

while(pos != null)

{

if( pos.getNext() != null )

if( pos.getData().compareTo(pos.getNext().getData() ) > 0

)

return false;

pos=pos.getNext();

} // while

return true;

} // isSorted

17

Class List methods – example2

Example2 – main and executions

public static void main(String args[ ]) { List<String> ls = new List<String>(); Node<String> last=null; for(int i=1; i<5;i++) { System.out.print(" enter the string "); String x=reader.next(); last= ls.insert(last, x); } // for System.out.println(ls); if(isSorted(ls)) System.out.println("YES"); else System.out.println("NO"); } // main

enter the string hello enter the string hi enter the string word enter the string bee [ hello, hi, word, bee ] NO

enter the string bee enter the string hello enter the string hi enter the string word [ bee, hello, hi, word ] YES

18

Class List methods - example 3

public static void remDuplications(List<Character> lst)

{

Node<Character> pos1= lst.getFirst();

while( pos1 != null ) {

char ch=pos1.getData();

pos2 = pos1.getNext();

while( pos2 != null ) {

if(pos2.getData() == ch)

pos2 = lst.remove(pos2);

else

pos2 = pos2.getNext();

} // inner while

pos1=pos1.getNext();

} // outer while

} // remDuplications

19

This method removes all duplications in Character type linked list.

s a b a a z null lst

s a b z null lst


public static void main (String[ ] args)

{

List<Character> ls = new List<Character>();

Node<Character> last = null;

System.out.print( " enter the character -> “ );

char x=reader.next().charAt(0);

while ( x !=‘*’ ) {


System.out.print( " enter the character -> “ );

x=reader.next().charAt(0);

} // while


remDuplications(ls);


}

20

enter the character -> a enter the character -> s enter the character -> a enter the character -> b enter the character -> a enter the character -> z enter the character -> * [ a, s, a, b, a, z ] [ a, s, b, z ]

sentinel

Merging two linked list

• Write a Java program that contains a method with the capability to merge two integer type sorted linked lists (lst1 and lst2) .

• The merged result should be in the third linked list (lst3) that is in sorted order. Do not destroy the original lists. Your program should output the content of three linked lists to show the program performs properly.

21

Method merge2Lists public static List<Integer> merge2Lists(List<Integer> lst1,List<Integer> lst2) {

Node<Integer> pos1=lst1.getFirst(), pos2=lst1.getFirst(), pos3=null;

List<Integer> lst3 = new List<Integer>();

while( pos1 != null && pos2 != null ) {

if( pos1.getData() > pos2.getData() ) {

pos3=lst3.insert(pos3,pos2.getData());


}

else {



} // if

} // while

while(pos1 != null) {



} // while

while(pos2 != null) {



} // while

return lst3;

} // merge2List

22

merge2Lists – main and executions public static void main(String[] args) {

List<Integer> lst1 = new List<Integer>(), lst2 = new List<Integer>();

Node<Integer> last = null;



while ( x != 777) {

last= lst1.insert(last, x);


x=reader.nextInt();

} // while

last=null;


x=reader.nextInt();

while ( x != 777) {

last= lst2.insert(last, x);


x=reader.nextInt();

} // while

List<Integer> lst3 = merge2Lists(ls1,ls2);

System.out.println(ls1);



} // main 23

enter an integer -> 1 enter an integer -> 2 enter an integer -> 5 enter an integer -> 8 enter an integer -> 9 enter an integer -> 777 enter an integer -> 3 enter an integer -> 4 enter an integer -> 7 enter an integer -> 777 [ 1, 2, 5, 8, 9 ] [ 3, 4, 7 ] [ 1, 2, 3, 4, 5, 7, 8, 9 ]

lst1

lst2

sentinel

sentinel


24

This method calculates the number of different values in the linked list.

public static int countDifItems(List<Integer> list) { Node<Integer> temp, pos = list.getFirst(); int count=0; // number of different values while(pos!=null) { temp=pos.getNext(); boolean found = false; // not found while(temp!=null) { if(temp.getData() == pos.getData()) { found = true; break; } // if temp = temp.getNext(); } // inner while if(!found) count++; pos = pos.getNext(); } // outer while return count; } // countDifItems

3


25

public static void main(String[] args) {





while ( x!=777) {



x=reader.nextInt();

} // while


System.out.println(“Count = " + countDifItems(ls));

} // main

enter an integer -> 1 enter an integer -> 2 enter an integer -> 1 enter an integer -> 2 enter an integer -> 5 enter an integer -> 777 [ 1, 2, 1, 2, 5 ] Count = 3


26

This method checks if the linked list of integer type is circular linked list .

public static boolean checkCircle(List<Integer> list) { Node<Integer> a=list.getFirst(); Node<Integer> b=list.getFirst(); while (b!=null) { a = a.getNext(); b = b.getNext(); if (b!=null) b=b.getNext(); else return false; if (a == b) return true; } // while return false; } // checkCircle

Tail


27

public static void main(String[ ] args)

{





while ( x!=777) {



x=reader.nextInt();

} //while


if(checkCircle(ls))

System.out.println("YES" );

else

System.out.println("NO" );

} // main

enter an integer -> 1 enter an integer -> 2 enter an integer -> 3 enter an integer -> 4 enter an integer -> 5 enter an integer -> 777 [ 1, 2, 3, 4, 5 ] YES

/* building circular linked list */

Node<Integer> pos=ls.getFirst();

Node<Integer> first=ls.getFirst();

while(pos.getNext() !=null )

pos=pos.getNext();

pos.setNext(first);

enter an integer -> 1 enter an integer -> 2 enter an integer -> 3 enter an integer -> 4 enter an integer -> 5 enter an integer -> 777 [ 1, 2, 3, 4, 5 ] NO

Class List recursive method1

28

This method tests if the number which passed as parameter exists in the

linked list of integer type.

public static boolean what1(List<Integer> lst, int num)

{

boolean ans; // returned value

int temp; // help variable

if( lst.isEmpty() )

ans = false;

else

{

temp=lst.getFirst().getData();

lst.remove(lst.getFirst());

ans = (temp == num) || what1(lst,num);

lst.insert(null,temp);

} // if

return ans;

} // what

Recursive methods1 debugging

29

public static boolean what1(List<Integer> lst, int num)

{

boolean ans; // returned value

int temp; // help variable

if( lst.isEmpty() )

ans = false;

else

{

temp=lst.getFirst().getData();

lst.remove(lst.getFirst());

ans = (temp == num) || what1(lst,num);

System.out.println("before insert temp"+lst);

lst.insert(null,temp);

System.out.println(“after insert temp"+lst);

} // if

return ans;

} // what1





[ 1, 2, 3 ]

enter search number -> 5

before insert temp [ ]

after insert temp [ 3 ]

before insert temp [ 3 ]

after insert temp [ 2, 3 ]

before insert temp [ 2, 3 ]

after insert temp [ 1, 2, 3

]

NO enter an integer -> 1




[ 1, 2, 3 ]


before insrt temp [ 3 ]


before insrt temp [ 2, 3 ]

after insert temp [ 1, 2, 3 ]

YES





[ 1, 2, 3 ]


before insert temp [ 3 ]


before insert temp [ 2, 3 ]

after insert temp [ 1, 2, 3 ]

YES

Linked list recursive method2

public static int what2(Node<Integer> lst)

{

if ( lst == null )

return 0;

Node<Integer> pos = lst.getNext();

int temp = what2(pos);

if(!(temp % 2 == 0) )

{

System.out.println( "temp= “ + temp);

System.out.println(pos.getData()); }

return temp + 1;

} // what2

30

This method take the reference to first element in the singly linked list as

parameter.

What is the output of the method for the following linked list ?

recursive method2 - solution

31

[ 1, 2, 3, 4, 5, 6, 7, 8, 9 ] temp=1 9 temp=3 7 temp=5 5 temp=7 3 what2= 9

public static void main(String[ ] args) {





while ( x!=777){



x=reader.nextInt();

}


Node<Integer> first = ls.getFirst();

System.out.println("what2= " + what2(first));

} // main

This will produce the next output :

Method what2 returns the number of elements in the

singly linked list.

Documents

Java linked list - cs.bgu.ac.ilipc131/wiki.files/Class_Java_9.pdf · collection of objects (nodes) which both carry the data we want to store and a reference to the next node in the