List Implementations That Link Data

1. List Implementations That Link Data Chapter 6

2. 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 Chapter Contents

3. 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

4. Linked Data A chain of 5 desks.

5. Forming a Chain • First desk placed in room • Blank desk top, no links • Address of the first chair given to teacher One desk in the room.

6. 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

7. Forming a Chain • Third desk arrives • New desk gets address of second desk • Instructor remembers address of new desk Three linked desks, newest desk first.

8. 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

9. Forming Another Chain Two linked desks, newest desk last.

10. Forming Another Chain Three linked desks, newest desk last.

11. Forming Another Chain Five linked desks, newest desk last.

12. 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

13. Adding New Desk: Case 1 Chain of desks prior to adding a new desk to beginning of the chain

14. Adding New Desk: Case 1 Addition of a new desk to beginning of a chain of desks

15. Adding New Desk: Case 2 Two consecutive desks within a chain prior to adding new desk between

16. Adding New Desk: Case 2 Addition of a new desk between two other desks.

17. 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

18. Removing Desk: Case 1 A chain of desks just prior to removing first desk.

19. Removing Desk: Case 1 A chain of desks just after removing first desk.

20. Removing Desk: Case 2 A chain of desks just prior to removing a desk between two other desks.

21. Removing Desk: Case 2 A chain of desks just after removing a desk between two other desks.

22. Removing Desk: Case 3 Before and after removing last desk from a chain.

23. 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)

24. 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 … }

25. Inner Class Node private class Node { private T data; //data value in that node entry private 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 }

26. 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

27. A Linked Implementation of the ADT List public class LList<T> implements ListInterface<T> { private Node firstNode; //head reference to fist node private Node lastNode; // tail reference to last node private int length; //number of entries in list public LList() { clear(); } //end constructor publicfinalvoid clear() { firstNode = null; lastNode = null; length = 0; } // end clear // implementation of the public methods add, remove, replace, getEntry, contains, getLength, isEmpty, isFull, and display… }

28. 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

29. 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.

30. Adding to the End of the List public boolean add(T newEntry) { Node newNode = new Node(newEntry); if (isEmpty()) firstNode = newNode; else lastNode.next = newNode; lastNode = newNode; length++; return true; }

31. 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.

32. 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

33. 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;

34. 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.

35. 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.

36. 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;

37. 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);

38. Using Class Node that Has Set and Get Methods private TgetData() { return data; } privatevoid setData(T newData) { data = newData; } private Node getNextNode() { return next; }

39. 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

40. Tail References A linked chain with a head and tail reference.

41. 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

42. Tail References Adding a node to the end of a nonempty chain that has a tail reference

43. 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

44. Java Class Library: The Class LinkedList • The standard java package java.util contains the class LinkedList • This class implements the interface List • Contains additional methods • addFirst() • addLast() • removeFirst() • removeLast() • getFirst() • getLast()