Outline Resource Introduction Usage Testing Exercises. Linked Lists COMP SCI / SFWR ENG 2S03. Department of Computing and Software McMaster University

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1 COMP SCI / SFWR ENG 2S03 Department of Computing and Software McMaster University Week 10: November 7 - November 11

2 Outline 1 Resource 2 Introduction Nodes Illustration 3 Usage Accessing and Modifying 4 Testing Exceptions Fixtures 5 Exercises Exercise 1 Exercise 2 Exercise 3 Exercise 4 Exercise 5

3 Resource Some of the following material is adapted from: Mughal, Khalid. Java Actually : A Comprehensive Primer in Programming. Australia: Course Technology/Cenage Learning, Virginia Tech for the Linked List image

4 Linked lists are dynamic data structures which A. Can create new data on demand B. Have an extra field to store a reference C. Data manipulation can be done by changing references

5 (continued) Some of the properties of linked lists include A. List of items which are called nodes B. Have a head and a tail Head points to the first node in the list Tail points to the last node in the list C. Every node has a pointer to the next node D. Because of this, lists are not limited in size like arrays!

6 Nodes Nodes are what make up a linked list. They are records which contain a data element as well as a pointer to the next element in the list. If the pointer is null, that means that the node is at the tail of the list. p u b l i c c l a s s Node<E> { p r i v a t e E data ; // E can be any type e x c e p t p r i m i t i v e s p r i v a t e Node next ;.. }

7 - Illustration

8 Using Java Java has a built-in linked list implementation that we will use. Linked lists can be created using any object type. import j a v a. u t i l. L i n k e d L i s t // Do t h i s always! L i n k e d L i s t <S t r i n g > s t r i n g s = new L i n k e d L i s t <S t r i n g >(); L i n k e d L i s t <I n t e g e r > i n t s = new L i n k e d L i s t <I n t e g e r >();

9 - Adding Items You can add elements to a linked list by A. Appending to the tail or B. Adding to a specific index // add (E element ) // add ( i n t index, E element ) l i s t. add ( " Hello, " ) ; l i s t. add ( 1, " world! " ) ;

10 - Getting Items We can get an item from a linked list if we know its index in the list using get. We can also get the index of an item from the list using indexof L i n k e d L i s t <S t r i n g > l i s t = new L i n k e d L i s t <S t r i n g >(); l i s t. add ( " h e l l o world " ) ; l i s t. add ( " one " ) ; l i s t. add ( "two" ) ; l i s t. get ( 0 ) ; // r e t u r n s " h e l l o world " l i s t. indexof ( "two" ) ; // r e t u r n s 2

11 - Setting Items We can set the value of an item from a linked list if we know its index in the list. L i n k e d L i s t <S t r i n g > l i s t = new L i n k e d L i s t <S t r i n g >(); l i s t. add ( " h e l l o world " ) ; l i s t. add ( " one " ) ; l i s t. add ( "two" ) ; // l i s t c o n t e n t s [ " h e l l o world " > " one " > "two " ] l i s t. s e t ( 0, " t e s t " ) ; // s e t s the v a l u e o f item at i n d e x 0 to " t e s t " // new l i s t c o n t e n t s : [ " t e s t " > " one " > "two " ]

12 - Finding and Removing We can remove an item from a linked list by its index value or by refering to the object itself L i n k e d L i s t <S t r i n g > l i s t = new L i n k e d L i s t <S t r i n g >(); l i s t. add ( " h e l l o world " ) ; l i s t. add ( " one " ) ; l i s t. add ( "two" ) ; l i s t. add ( " t h r e e " ) // l i s t c o n t e n t s [ " h e l l o world " > " one " // > "two" > " t h r e e " ] l i s t. remove ( 0 ) ; // l i s t c o n t e n t s [ " one " > "two" > " t h r e e " ] l i s t. remove ( "two" ) // l i s t c o n t e n t s [ " one " > " t h r e e " ]

13 Testing for Exceptions Using JUnit you can test for an exception being thrown by your code such as A. IndexOutOfBoundsException B. IOException C. ArithmeticException

14 Testing for Exceptions - ( e x p e c t e d= IndexOutOfBoundsException. c l a s s ) p u b l i c void empty ( ) { new L i n k e d L i s t <I n t e g e r >(). get ( 0 ) ; }

15 Testing Fixtures Using JUnit, you can also specify the state of your program pre-class or pre-test

16 Testing Fixtures - B e f o r e C l a s s p u b l i c s t a t i c void s e t u p ( ) { Point t e s t P o i n t = new Point ( 0, 5 ) ; i n t t e s t V a l u e = 5 ; }

17 Exercises There are many methods that are provided by Java for linked lists. You can find them online at util/linkedlist.html In the exercises that follow, be sure to refer to the documentation for any methods not mentioned here!

18 Exercise 1 Given a sorted singly linked list, write a method which takes an element and returns the list with that element inserted such that the list is still sorted. < 1, 2, 5, 6, 8, 9 > +7 < 1, 2, 5, 6, 7, 8, 9 > Hint: you should use the following specification to create this function p u b l i c s t a t i c L i n k e d L i s t <I n t e g e r > i n s e r t S o r t e d ( L i n k e d L i s t <I n t e g e r > l i s t, I n t e g e r number ) { // your code h e r e }

19 Exercise 2 Given a singly linked list, write a method which takes two index values and swaps the values contained within those indices in the list. For this exercise, just use a list of integers. < 1, 2, 5, 6, 8, 9 > < 1, 8, 5, 6, 2, 9 > Hint: you should use the following specification to create this function p u b l i c s t a t i c L i n k e d L i s t <I n t e g e r > swap ( L i n k e d L i s t <I n t e g e r > l i s t, i n t f i r s t, i n t second ) { // your code h e r e }

20 Exercise 3 Given a singly linked list, write a method which traverses the list searching for a specific element. If that element is found, then the method returns true, otherwise it returns false. Hint: you should use the following specification to create this function p u b l i c s t a t i c boolean s e a r c h ( L i n k e d L i s t <I n t e g e r > l i s t, I n t e g e r term ) { // your code h e r e }

21 Exercise 4 Let s try something new. A doubly linked list is a type of linked list where the nodes point both forward to the next element and backward to the previous element. Therefore the element at index 2 points back to index 1 but also points forward to index 3 (assuming it is not the tail!) Your job is to create your own implementation of a doubly linked list. Your class should have the ability to add, find, and delete elements from the list. Hint: Start by creating a class DoublyLinkedList with a subclass Node. Use these two classes to implement the same linked lists we have been using, except with the added property that the nodes have information about the previous node in the list.

22 Exercise 4 Figure: Illustration of a doubly linked list. Note the pointers to the previous element!

23 Exercise 5 There s more where that came from! A circular linked list is a type of linked list where the tail points around back to the head of the list. Your job is create your own implementation of a circular linked list and add the same functionality as above! Hint: Start by creating a class CircularLinkedList with a subclass Node. Use these two classes to implement the same linked lists we have been using, except with the added property that the tail points to the head of the list. Not as hard as it sounds!