List Implementations That Link Data

Chapter 6

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Chapter Contents

Linked Data• Forming a Chains

The Class Node

A Linked Implementation• Adding to End of List• Adding at Given

Position• Method remove• Method replace• Method getEntry

• Method contains• Remaining methods• Using a Class Node

with Set and Get Methods

Tail References• Revision of List

Pros and Cons of Using Chain

Java Class Library:LinkedList

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Linked Data

Consider the analogy of desks in a classroom• Placed in classroom as needed• Each desk has a unique id, the “address”• The desks are linked by keeping the address

of another chair• We have a chain of chairs

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Linked Data

A chain of 5 desks.

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Forming a ChainFirst desk placed in room• Blank desk top, no links• Address of the first chair given to teacher

One desk in the room.

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Forming a Chain

Second student arrives, takes a desk• Address of first desk placed on new desk• Instructor “remembers” address of new desk

Two linked desks

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Forming a ChainThird desk arrives• New desk gets address of second desk• Instructor remembers address of new desk

Three linked desks, newest desk first.

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Forming Another Chain

This time the first student is always at the beginning of the chain• Instructor only remembers first address

The address of a new desk is placed on the previous desk (at end of chain)• End of chain found by following links • Newest desk does not have a pointer address

to any other desk

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Forming Another Chain

Two linked desks, newest desk last.

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Forming Another Chain

Three linked desks, newest desk last.

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Forming Another Chain

Five linked desks, newest desk last.

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Adding New Desk

Consider the requirement to organize the chain alphabetically• New arrivals are placed somewhere in the

chain, not necessarily at the end

Possibilities for placement of a new desk• Case 1: Before all current desks• Case 2: Between two existing desks• Case 3: After all current desks

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Adding New Desk: Case 1

Chain of desks prior to adding a new desk to beginning of the chain

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Adding New Desk: Case 1

Addition of a new desk to beginning of a chain of desks

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Adding New Desk: Case 2

Two consecutive desks within a chain prior to adding new desk between

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Adding New Desk: Case 2

Addition of a new desk between two other desks.

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Removing Desk

Removing an item from a chain

Possible cases• Case 1: Desk to be removed is first in the

chain• Case 2: Desk to be removed is between two

current desks• Case 3: Desk to be removed is last in the

chain

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Removing Desk: Case 1

A chain of desks just prior to removing first desk.

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Removing Desk: Case 1

A chain of desks just after removing first desk.

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Removing Desk: Case 2

A chain of desks just prior to removing a desk between two other desks.

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Removing Desk: Case 2

A chain of desks just after removing a desk between two other desks.

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Removing Desk: Case 3

Before and after removing last desk from a chain.

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The Class Node

Nodes are objects that are linked together to form a data structure

We will use nodes with two data fields• A reference to an entry in the list

• (the person sitting at the desk)

• A reference to another node • (the address on the paper on the desk)

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The Class Node

Two linked nodes with (a) primitive data; (b) class/object data

private class Node

{

private T data; //data value in that node entry

private Node next; //link to next node

…

}

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Inner Class Nodeprivate class Node{

private T data; //data value in that node entryprivate Node next; //link to next node

private Node (T dataPortion){

data = dataPortion;next = null;

} //end constructor

private Node( T dataPortion, Node nextNode){

data = dataPortion;next = nextNode;

} // end constructor

}

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A Linked Implementation of the ADT List

Use a chain of nodes• Remember the address of the first node in the

chain

Record a reference to the first node• The “head reference”

The implementation contains the class Node as an inner class

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A Linked Implementation of the ADT List

public class LList<T> implements ListInterface<T>{

private Node firstNode; //head reference to fist nodeprivate Node lastNode; // tail reference to last nodeprivate int length; //number of entries in list

public LList(){

clear();} //end constructor

public final void clear() {

firstNode = null;lastNode = null;length = 0;

} // end clear

// implementation of the public methods add, remove, replace, getEntry, contains, getLength, isEmpty, isFull, and display…

}

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Adding to the End of An empty List

(a) An empty list and a new node;(b) after adding a new node to a list that was empty

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Adding to the End of An Non-empty List

A chain of nodes (a) just prior to adding a node at the end; (b) just after adding a node at the end.

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Adding to the End of the List

public boolean add(T newEntry) {

Node newNode = new Node(newEntry);

if (isEmpty())firstNode = newNode;

elselastNode.next = newNode;

lastNode = newNode;

length++;return true;

}

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Adding to the Beginning of the List

A chain of nodes (a) prior to adding a node at the beginning; (b) after adding a node at the beginning.

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Adding at a Given Position Within the List

A chain of nodes (a) prior to adding node between adjacent nodes; (b) after adding node between

adjacent nodes

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Adding at a Given Position Within the List

The following Java Statements implement these steps:• Node newNode = new Node(newEntry);• Node nodeBefore = getNodeAt(newPosition -1);• Node nodeAfter = nodeBefore.next;• newNode.next = nodeAfter;• nodeBefore.next = newNode;

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Removing the first node

A chain of nodes (a) prior to removing first node; (b) after removing the first node

Need to see if there is only one node, if yes, update the lastnode.

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Removing other than the beginning of the list

A chain of nodes (a) prior to removing interior node; (b) after removing interior node

Need to see if nodeToRemove is at the end, if yes, update the lastnode.

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The Method remove: first node

firstNode = firstNode.next;

The Method remove: other than the beginning

Node nodeBefore = getNodeAt(givenPosition -1);

Node nodeToRemove = nodeBefore.next;

Node nodeAfter = nodeToRemove.next;

nodeBefore.next = nodeAfter;

nodeToRemove = null;

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Using Class Node that Has Set and Get Methods

Class Node is an inner class• The class LList can access private data

fields directly

• Stylistically better to use the Set and Get methods of the class Node

Thus better to use statements such as:currentNode.getData(); ordesiredNode.setData(newEntry);

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Using Class Node that Has Set and Get Methods

private T getData(){

return data;}private void setData(T newData){

data = newData;}

private Node getNextNode(){

return next;}

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Tail References

Consider a set of data where we repeatedly add data to the end of the list

Each time the getNodeAt method must traverse the whole list• This is inefficient

Solution: maintain a pointer that always keeps track of the end of the chain• The tail reference

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Tail References

A linked chain with a head and tail reference.

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Tail References

When adding to an empty list• Both head and tail references must point to the

new solitary node

When adding to a non empty list• No more need to traverse to the end of the list• lastNode points to it

• Adjust lastNode.next to new node and lastNode to new node

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Tail References

Adding a node to the end of a nonempty chain that has a tail reference

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Pros and Cons of a Chain for an ADT List

The chain (list) can grow as large as necessary

Can add and remove nodes without shifting existing entries

But …

Must traverse a chain to determine where to make addition/deletion

Retrieving an entry requires traversal• As opposed to direct access in an array

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Java Class Library: The Class LinkedList

The standard java package java.util contains the class LinkedListThis class implements the interface ListContains additional methods

•addFirst()•addLast()•removeFirst()•removeLast()•getFirst()•getLast()