P13 - Linked Lists

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Objectives of this Assignment

1. Practice implementing Linked List methods
2. Implement a simple book system

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Description

In this assignment we will implement a singly linked list class to get a better understanding of this reference-based data structure. The interface you will implement is very similar to that provided by ArrayLists, but the way in which they are implemented is very different.

Phase 1 - Build the project

You should have built the project in recitation. If you didn't, please perform Recitation 20.

Phase 2 - File Descriptions

Book.java

Book.java is nothing out of the ordinary - it's just keeps track of the book's title and its author, as well as the number of pages. It has a few getter and setter methods, but overall this class is very straight forward.

BookNode.java

BookNode.java is a little more interesting. A BookNode is an object that stores a Book in its book instance variable, and has a reference to the next BookNode in its next instance variable. If the node is the last one in the sequence, its next variable will be set to null. There are also methods for setting the next node and getting the next node, as well as a method for returning the book that the node contains.

LinkedBookList.java

Now let's look at the LinkedBookList class. You'll see that the instance variables for this are very simple. Only a BookNode called head, which refers to the first item, and an int to keep track of the size of the linked list. This is all we need, since each element contains a reference to the next one.

R20.java

R20.java is your test program to run and add test cases to.

Phase 3 - Implementation

Your task is to implement the missing add, totalPages, and remove methods per the instructions.

All these methods will require you to iterate through the list. You can do this either with a while loop or a for loop. If using a for loop, think what are the three components that make up the loop:

(initialization; are we done?; operation to reach the next item) 

Many of the operations that we are trying to implement here, can be reasoned through by drawing pictures. Use that to reason how far to go, when to set which pointers, and when to delete pointers.

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My Recitation project code for Lab20

public class LinkedBookList {

private BookNode head;

private int size;

public LinkedBookList(){

head = null;

size = 0;

}

//returns size of the list

public int size(){

return size;

}

//IMPLEMENT -- adds a book to the end of the linked list

public void add(Book b){

add(b,size);

}

//IMPLEMENT -- adds a book at the specific index,

// or at the end if index is greater than size

public void add(Book b, int index){

BookNode bb = new BookNode(b);

BookNode tpp = head;

if(index==0)

{

bb.setNext(head);

this.head=bb;

}

else

{

for(int kk=1;kk

{

tpp=tpp.getNext() ;

}

bb.setNext(tpp.getNext());

tpp.setNext(bb);

}

size++;

}

//IMPLEMENT -- removes a book and returns it, or

// returns null if book is not present

public Book remove(Book b){

BookNode bb=head;

if(head==null)

return null;

int indx=-1;

int tpp=0;

while(bb!=null)

{

Book mybk=bb.getBook() ;

if(b.getAuthor().equals(mybk.getAuthor()))

{

indx = tpp;

break;

}

else

{

bb = bb.getNext();

tpp++;

}

}

return remove(indx);

}

//IMPLEMENT -- removes a book at a specific index and returns it,

// or returns null if index is not present

public Book remove(int index){

if(index<0)

return null;

else if(index>=size)

return null;

BookNode tpp = head;

BookNode ptr = null;

if(index==0)

{

head = head.getNext();

}

else

{

for(int i=1; i

{

tpp = tpp.getNext() ;

}

tpp.setNext(tpp.getNext());

}

size--;

return tpp.getBook();

}

//IMPLEMENT -- returns the total number of pages in the linked list

public int totalPages(){

int res = 0;

for (BookNode pos = head; pos != null; pos = pos.getNext())

{

if (pos.getBook() != null)

{

Book b=pos.getBook();

res += b.getNumPages();

}

}

return res;

}

public String toString()

{

String res = "";

for (BookNode pos = head; pos != null; pos = pos.getNext()) {

if (pos.getBook() == null) {

res += "null";

} else {

res += pos.getBook();

}

if (pos.getNext() != null) res += " ";

}

return res;

}

}