1. CS2006- Data Structures I
Chapter 5 Linked Lists I

2. Topics Linked List and Array Object & Reference
Reference-Based Linked List

3. Array Limitations Arrays Is there any other way to implement the list?
Simple
Fast, easy to perform search
but
Difficult to insert and delete items
Must specify size at construction time
Is there any other way to implement the list?

4. Linked Lists
Fortunately, we can use a structure called a linked list to overcome this limitation.
The linked list is a very flexible dynamic data structure: items may be added to it or deleted from it at will.
A linked list allows as many elements as a programmer needs requiring much less maintenance.

5. Object & References class Student { }
String name;
int ID;
double GPA;
Address address; }
class variables (instance variable) are initialized by compiler automatically.
Name = null;
ID=0;
GPA=0.0;
address=null; //object references are initialized with null

6. Object & References Create a reference to a type student
Student student;
student is called a reference variable (or reference) of type Student
it contains the address of an object or null;
the object needs to be created using new ?

7. Object & References
A reference can also be called a pointer (to an object in memory) and they are often depicted graphically:
student = new Student (“John Smith”, 40725, 3.57)
student
John Smith
40725
3.57

8. Object & References
student = null;
This means that student reference does not “point” to any object
student

9. References as Links
Object references can be used to create links between objects
Suppose a Student class contained a reference to another Student object (code?)
John Smith
40725
3.57
Jane Jones
58821
3.72

10. References as Links
References can be used to create a variety of linked structures, such as a linked list:
studentList

11. Objects
Two objects of this class can be instantiated and chained together having the next reference of one Node object refer to the other.
The second object’s next reference can refer to a third Node object, and so on, creating a linked list of Node objects.
Each node will contain some data as specified by the programmer. This constitutes a linked list

12. Linked List Definition
A collection of data items of the same type that are stored in separate objects referred to as "nodes".
Each node contains, in addition to its data value(s), a reference to an object of the same type.

13. Linked Lists
List: An external reference usually referred to as the "head" of the list contains the address of the first node object.
Diagram of a sample linked list containing int data:
Node
NULL
pointer 45 51 84
Head
Node
Item
Next

14. A Linked List Node Class
First attempt at a class for a linked list of integers:
public class IntegerNode {
public int item;
public IntegerNode next; }
Problem?

15. Final IntegerNode Class
public class IntegerNode {
private int item;
private IntegerNode next;
public IntegerNode(int newItem) {
item = newItem;
next = null;
} // end constructor
public IntegerNode(int newItem, IntegerNode nextNode) {
next = nextNode;

16. Final IntegerNode Class (2)
public void setItem(int newItem) {
item = newItem;
} // end setItem
public int getItem() {
return item;
} // end getitem
public void setNext(IntegerNode nextNode) {
next = nextNode;
} // end setNext
public IntegerNode getNext() {
return next;
} // end getNext
} // end class IntegerNode

17. A Polymorphic Linked List Node
public class Node {
private Object item;
private Node next;
public Node(Object newItem) {
item = newItem;
next = null;
} // end constructor
public Node(Object newItem, Node nextNode) {
next = nextNode;

18. A Polymorphic Linked List Node
public class Node {
private Object item;
private Node next;
public Node(Object newItem) {
item = newItem;
next = null;
} // end constructor
public Node(Object newItem, Node nextNode) {
next = nextNode;

19. A Polymorphic Linked List Node
public void setItem(Object newItem) {
item = newItem;
} // end setItem
public Object getItem() {
return item;
} // end getitem
public void setNext(Node nextNode) {
next = nextNode;
} // end setNext
public Node getNext() {
return next;
} // end getNext
} // end class Node
To instantiate a Node containing
an Integer:
Node n = new Node(new Integer(6));
or containing a character:
Node n = new Node(new Character('A'));

20. A Polymorphic Linked List Node
public void setItem(Object newItem) {
item = newItem;
} // end setItem
public Object getItem() {
return item;
} // end getitem
public void setNext(Node nextNode) {
next = nextNode;
} // end setNext
public Node getNext() {
return next;
} // end getNext
} // end class Node
To instantiate a Node containing
an Integer:
Node n = new Node(new Integer(6));
or containing a character:
Node n = new Node(new Character('A'));

21. Review
When you declare a variable that refers to an object of a given class, you are creating a(n) ______ to the object.
interface
reference
method
ADT

22. Review Integer maxNum; maxNum = new Integer (15);
______ is a reference variable.
Integer
maxNum
New 15

23. Review
A reference variable declared as a data field within a class has the default value ______. -1
null
empty

24. Review
If you attempt to use a reference variable before it is instantiated, a(n) ______ will be thrown.
IndexOutOfBoundsException
InstantiationException
IllegalAccessException
NullPointerException

25. Review
A linked list contains components, called ______, which are linked to one another.
nodes
arrays
vectors
references

26. Review
According to the principle of information hiding, the data fields of a class must be declared as ______.
public
protected
private
abstract