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CS2006- Data Structures I
Chapter 5
Linked Lists I
Topics
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Linked List and Array
Object & Reference
Reference-Based Linked List
Array Limitations
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Arrays
Simple
 Fast, easy to perform search
but
 Difficult to insert and delete items
 Must specify size at construction time
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Is there any other way to implement the list?
Linked Lists
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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.
Object & References
class Student {
String name;
int ID;
double GPA;
Address address;
}
class variables (instance variable) are initialized by
compiler automatically.
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Name = null;
ID=0;
GPA=0.0;
address=null; //object references are initialized with null
Object & References
student
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Create a reference to a type
?
Student student;
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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
Object & References
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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
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John Smith
40725
3.57
Object & References
student = null;
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This means that student reference does not
“point” to any object
student
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References as Links
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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
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Jane Jones
58821
3.72
References as Links
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References can be used to create a
variety of linked structures, such as a
linked list:
studentList
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Objects
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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
Linked List Definition
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Linked List:
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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.
Linked Lists
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List: An external reference usually referred to as the
"head" of the list contains the address of the first
node object.
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Diagram of a sample linked list containing int
data:
Head
45
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Node
51
84
Node
Item
Next
NULL
pointer
A Linked List Node Class
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First attempt at a class for a linked list of
integers:
public class IntegerNode {
public int item;
public IntegerNode next;
}
Problem?
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) {
item = newItem;
next = nextNode;
} // end constructor
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
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) {
item = newItem;
next = nextNode;
} // end constructor
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) {
item = newItem;
next = nextNode;
} // end constructor
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'));
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'));
Review
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When you declare a variable that refers to
an object of a given class, you are
creating a(n) ______ to the object.
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interface
reference
method
ADT
Review
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Integer maxNum;
maxNum = new Integer (15);
______ is a reference variable.
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Integer
maxNum
New
15
Review
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A reference variable declared as a data
field within a class has the default value
______.
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0
-1
null
empty
Review
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If you attempt to use a reference variable
before it is instantiated, a(n) ______ will
be thrown.
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IndexOutOfBoundsException
InstantiationException
IllegalAccessException
NullPointerException
Review
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A linked list contains components, called
______, which are linked to one another.
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nodes
arrays
vectors
references
Review
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According to the principle of information
hiding, the data fields of a class must be
declared as ______.
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public
protected
private
abstract