1. A Bag Implementation that Links Data
Chapter 3
Adapted from Pearson Education, Inc.

2. Contents The private inner class Node Creating a Linked Chain
Removing Items from a Linked Chain
The Pros and Cons of Using a Chain to Implement the ADT Bag
Adapted from Pearson Education, Inc.

3. Objectives Describe linked organization of data
Describe how to add new node to beginning of chain of linked nodes
Describe how to remove first node in chain of linked nodes
Describe how to locate particular piece of data within chain of linked nodes
Implement ADT bag by using chain of linked nodes
Describe differences between array-based and linked implementations of ADT bag
Adapted from Pearson Education, Inc.

4. Class Node
The private class Node
Adapted from Pearson Education, Inc.

5. A Linked Implementation of the ADT Bag
public class LinkedBag < T > implements BagInterface < T > { private Node firstNode; // reference to first node private int numberOfEntries; public LinkedBag () { firstNode = null; numberOfEntries = 0; } // end default constructor // Implementations of the public methods // of BagInterface go here. private class Node // private inner class { private T data; // entry in bag private Node next; // link to next node private Node (T dataPortion) { this (dataPortion, null); } private Node (T dataPortion, Node nextNode) { data = dataPortion; next = nextNode; } // end constructor } // end Node } // end LinkedBag
Adapted from Pearson Education, Inc.

6. Adding first item to an empty chain
Figure 3-6
An empty chain and
a new node;
after adding a new node
to the empty chain
Adapted from Pearson Education, Inc.

7. Adding a node at the beginning of a chain
Figure 3-7
A chain and
a new node;
The chain after adding the new node
Adapted from Pearson Education, Inc.

8. Method add
Adapted from Pearson Education, Inc.

9. Method toArray ( currentNode != null )
Adapted from Pearson Education, Inc.

10. Method getFrequencyOf
Adapted from Pearson Education, Inc.

11. Method getFrequencyOf
( currentNode != null )
We can get rid of the integer variable counter
Adapted from Pearson Education, Inc.

12. Method contains
Adapted from Pearson Education, Inc.

13. Method contains return true;
We can get rid of the boolean variable found
false;
Adapted from Pearson Education, Inc.

14. Removing an Item from a Linked Chain
Case 1
Your item is first in the chain of items.
Steps required
Locate first item by checking firstNode.
Check next of first item and make it the new firstNode.
Get rid of the first item.
firstNode
next
Adapted from Pearson Education, Inc.

15. Removing an Item from a Linked Chain
Case 2
Desired item is NOT first in the chain of items.
Steps required:
Find reference to Desired item
Move data from the first item in place of desired item.
Remove first item using steps described for Case 1.
xyz
abc
klm
Desired item
First item
xyz
abc
klm
Desired item
Adapted from Pearson Education, Inc.

16. Method remove …(Case 1)
Adapted from Pearson Education, Inc.

17. Method remove …(Case 2)
Adapted from Pearson Education, Inc.

18. Method remove …(Case 2) Do we need the boolean variable result?
return currentNode;
Do we need the boolean variable result?
Did we forget anything before returning?
Adapted from Pearson Education, Inc.

19. Method clear
Adapted from Pearson Education, Inc.

20. Pros and Cons of Using a Chain
Bag can grow and shrink in size as necessary
Possible to remove and recycle nodes
Copying values for array enlargement not needed
Removing specific value entry requires search of array or chain
Chain requires more memory than array of same length
Why?
Adapted from Pearson Education, Inc.

21. End
Chapter 3
Adapted from Pearson Education, Inc.