Csphtp1 23

Chapter 23 – Data Structures Outline 23.1 Introduction 23.2 Self-Referential Classes 23.3 Linked Lists 23.4 Stacks 23.5 Queues 23.6 Trees 23.6.1 Binary Search Tree of Integer Values 23.6.2 Binary Search Tree of IComparable Objects 23.7 Collection Classes 23.7.1 Class Array 23.7.2 Class ArrayList 23.7.3 Class Stack 23.7.4 Class Hashtable

23.1 Introduction Dynamic data structures Grow and shrink at execution time Linked Lists: Lined up in a row Insertions and removals can occur anywhere in the list Stacks: Insertions and removals only at top Queues: Insertions made at back, removals from front Binary Trees: Facilitate high-speed searching and sorting of data Efficient elimination of duplicate items

23.2 Self-Referential Classes Contains a reference member to an object of the same class type Reference can be used to link objects of the same type together Dynamic data structures require dynamic memory allocation Ability to obtain memory when needed and release memory when it is not needed Uses new operator Ex: Node nodeToAdd = new Node(10);

23.2 Self-Referential Class 1 class Node 2 { 3 private int data; 4 private Node next; 5 6 public Node( int d ) 7 { 8 /* constructor body */ 9 } 10 11 public int Data 12 { 13 get 14 { 15 /* get body */ 16 } 17 Fig. 23.1 Sample self-referential Node class definition (part 1) Reference to object of same type

23.2 Self-Referential Class 18 set 19 { 20 /* set body */ 21 } 22 } 23 24 public Node Next 25 { 26 get 27 { 28 /* get body */ 29 } 30 31 set 32 { 33 /* set body */ 34 } 35 } 36 } Fig. 23.1 Sample self-referential Node class definition (part 2)

23.2 Self-Referential Class Fig. 23.2 Two self-referential class objects linked together. 15 10

23.3 Linked Lists Linked List: Linear collection of self-referential nodes connected by links Nodes: class objects of linked-lists Programs access linked lists through a reference to first node Subsequent nodes accessed by link-reference members Last node’s link set to null to indicate end of list Nodes can hold data of any type Nodes created dynamically Similar to arrays, however: Arrays are a fixed size Linked lists have no limit to size More nodes can be added as program executes

23.3 Linked Lists Fig. 23.3 A graphical representation of a linked list. H D …… Q firstNode lastNode

LinkedListLibrary.cs 1 // Fig. 23.4: LinkedListLibrary.cs 2 // Class ListNode and class List definitions. 3 4 using System; 5 6 namespace LinkedListLibrary 7 { 8 // class to represent one node in a list 9 class ListNode 10 { 11 private object data; 12 private ListNode next; 13 14 // constructor to create ListNode that refers to dataValue 15 // and is last node in list 16 public ListNode( object dataValue ) 17 : this ( dataValue, null ) 18 { 19 } 20 21 // constructor to create ListNode that refers to dataValue 22 // and refers to next ListNode in List 23 public ListNode( object dataValue, ListNode nextNode ) 24 { 25 data = dataValue; 26 next = nextNode; 27 } 28 29 // property Next 30 public ListNode Next 31 { 32 get 33 { 34 return next; 35 } Reference to next ListNode in linked list Accessor method so a List can access next member variable Constructor for first item in list Invoke normal constructor, which will set data to dataValue and next to null Constructor to set data and next values to parameter values

LinkedListLibrary.cs 36 37 set 38 { 39 next = value; 40 } 41 } 42 43 // property Data 44 public object Data 45 { 46 get 47 { 48 return data; 49 } 50 } 51 52 } // end class ListNode 53 54 // class List definition 55 public class List 56 { 57 private ListNode firstNode; 58 private ListNode lastNode; 59 private string name; // string like "list" to display 60 61 // construct empty List with specified name 62 public List( string listName ) 63 { 64 name = listName; 65 firstNode = lastNode = null ; 66 } 67 Accessor method so a List can access data member variable Reference to first node in list Reference to last node in list Set reference to first and last nodes to null

LinkedListLibrary.cs 68 // construct empty List with "list" as its name 69 public List() : this ( "list" ) 70 { 71 } 72 73 // Insert object at front of List. If List is empty, 74 // firstNode and lastNode will refer to same object. 75 // Otherwise, firstNode refers to new node. 76 public void InsertAtFront( object insertItem ) 77 { 78 lock ( this ) 79 { 80 if ( IsEmpty() ) 81 firstNode = lastNode = 82 new ListNode( insertItem ); 83 else 84 firstNode = 85 new ListNode( insertItem, firstNode ); 86 } 87 } 88 89 // Insert object at end of List. If List is empty, 90 // firstNode and lastNode will refer to same object. 91 // Otherwise, lastNode's Next property refers to new node. 92 public void InsertAtBack( object insertItem ) 93 { 94 lock ( this ) 95 { 96 if ( IsEmpty() ) 97 firstNode = lastNode = 98 new ListNode( insertItem ); 99 Method to insert an object at the front of the list Test if list is empty Get list lock If list is empty, create new node and set firstNode and lastNode to refer to it If list is not empty, insert object by setting its next reference to the first node Method to insert object into back of list Get list lock Test if list is empty If list is empty create a new node and set firstNode and lastNode to reference it

LinkedListLibrary.cs 100 else 101 lastNode = lastNode.Next = 102 new ListNode( insertItem ); 103 } 104 } 105 106 // remove first node from List 107 public object RemoveFromFront() 108 { 109 lock ( this ) 110 { 111 object removeItem = null ; 112 113 if ( IsEmpty() ) 114 throw new EmptyListException( name ); 115 116 removeItem = firstNode.Data; // retrieve data 117 118 // reset firstNode and lastNode references 119 if ( firstNode == lastNode ) 120 firstNode = lastNode = null ; 121 122 else 123 firstNode = firstNode.Next; 124 125 return removeItem; // return removed data 126 } 127 } 128 129 // remove last node from List 1 30 public object RemoveFromBack() 131 { 132 lock ( this ) 133 { 134 object removeItem = null ; If list is not empty, create a new node and set the last node’s next reference to the new node Method to remove an object from the front of list Get lock Throw exception if list is empy Set removeItem equal to data in first node If there is only one node in the list, set firstNode and lastNode references to null If there is more then one node, set firstNode to reference the second node Return data stored in node Method to remove an object from the back of the list

LinkedListLibrary.cs 135 136 if ( IsEmpty() ) 137 throw new EmptyListException( name ); 138 139 removeItem = lastNode.Data; // retrieve data 140 141 // reset firstNode and lastNode references 142 if ( firstNode == lastNode ) 143 firstNode = lastNode = null ; 144 145 else 146 { 147 ListNode current = firstNode; 148 149 // loop while current node is not lastNode 150 while ( current.Next != lastNode ) 151 current = current.Next; // move to next node 152 153 // current is new lastNode 154 lastNode = current; 155 current.Next = null ; 156 } 157 158 return removeItem; // return removed data 159 } 160 } 161 162 // return true if List is empty 163 public bool IsEmpty() 164 { 165 lock ( this ) 166 { 167 return firstNode == null ; 168 } 169 } Set removeItem equal to the data in the last node If there is only one node, set firstNode and lastNode to refer to null Loop until next to last node is reached Set lastNode to refer to the next to last node Set reference of new last node to null Return data of old last node Method to test if list is empty

LinkedListLibrary.cs 170 171 // output List contents 172 virtual public void Print() 173 { 174 lock ( this ) 175 { 176 if ( IsEmpty() ) 177 { 178 Console.WriteLine( "Empty " + name ); 179 return ; 180 } 181 182 Console.Write( "The " + name + " is: " ); 183 184 ListNode current = firstNode; 185 186 // output current node data while not at end of list 187 while ( current != null ) 188 { 189 Console.Write( current.Data + " " ); 190 current = current.Next; 191 } 192 193 Console.WriteLine( "\n" ); 194 } 195 } 196 197 } // end class List 198 Method to output the list Tell user if list is empty Output data in list

LinkedListLibrary.cs 199 // class EmptyListException definition 200 public class EmptyListException : ApplicationException 201 { 202 public EmptyListException( string name ) 203 : base ( "The " + name + " is empty" ) 204 { 205 } 206 207 } // end class EmptyListException 208 209 } // end namespace LinkedListLibrary Handles illegal operations on an empty list

ListTest.cs 1 // Fig 23.5: ListTest.cs 2 // Testing class List. 3 4 using System; 5 using LinkedListLibrary; 6 7 namespace ListTest 8 { 9 // class to test List class functionality 10 class ListTest 11 { 12 static void Main( string [] args ) 13 { 14 List list = new List(); // create List container 15 16 // create data to store in List 17 bool aBoolean = true ; 18 char aCharacter = '$' ; 19 int anInteger = 34567 ; 20 string aString = "hello" ; 21 22 // use List insert methods 23 list.InsertAtFront( aBoolean ); 24 list.Print(); 25 list.InsertAtFront( aCharacter ); 26 list.Print(); 27 list.InsertAtBack( anInteger ); 28 list.Print(); 29 list.InsertAtBack( aString ); 30 list.Print(); 31 32 // use List remove methods 33 object removedObject; 34 Create list of objects Insert objects at beginning of listinto list using InsertAtFront method Insert objects at end of listinto list using InsertAtBack method Print the list Create data to put in list

ListTest.cs 35 // remove data from list and print after each removal 36 try 37 { 38 removedObject = list.RemoveFromFront(); 39 Console.WriteLine( removedObject + " removed" ); 40 list.Print(); 41 42 removedObject = list.RemoveFromFront(); 43 Console.WriteLine( removedObject + " removed" ); 44 list.Print(); 45 46 removedObject = list.RemoveFromBack(); 47 Console.WriteLine( removedObject + " removed" ); 48 list.Print(); 49 50 removedObject = list.RemoveFromBack(); 51 Console.WriteLine( removedObject + " removed" ); 52 list.Print(); 53 } 54 55 // process exception if list empty when attempt is 56 // made to remove item 57 catch ( EmptyListException emptyListException ) 58 { 59 Console.Error.WriteLine( "\n" + emptyListException ); 60 } 61 62 } // end method Main 63 64 } // end class ListTest 65 } Remove objects from front of list using method RemoveFromFront Remove objects from back of list using method RemoveFromBack Print the list after each remove If remove is called on an empty list tell user

ListTest.cs Program Output The list is: True The list is: $ True The list is: $ True 34567 The list is: $ True 34567 hello $ removed The list is: True 34567 hello True removed The list is: 34567 hello hello removed The list is: 34567 34567 removed Empty list

23.3 Linked Lists Fig. 23.6 A graphical representation of the InsertAtFront operation. 11 7 12 new ListNode (a) firstNode 12 new ListNode 11 7 firstNode (b)

23.3 Linked Lists Fig. 23.7 A graphical representation of the InsertAtBack operation. (a) 7 12 New ListNode 11 5 firstNode lastNode 7 11 firstNode New ListNode (b) 12 5 lastNode

23.3 Linked Lists Fig. 23.8 A graphical representation of the RemoveFromFront operation. (a) 7 12 lastNode 11 5 firstNode 7 11 firstNode lastNode (b) 12 5 removeItem

23.3 Linked Lists Fig. 23.9 A graphical representation of the RemoveFromBack operation. (a) 7 12 lastNode 11 5 firstNode 7 11 firstNode lastNode (b) 12 5 current removeItem

23.4 Stacks Special version of linked list: Last-in, first-out (LIFO) data structure: Takes and releases new nodes only at top Operations: Push: adds new node to top of stack Pop: removes top node from stack Can be used for: Storing return addresses Storing local variables

StackInheritanceLibrary.cs 1 // Fig. 23.10: StackInheritanceLibrary.cs 2 // Implementing a stack by inheriting from class List. 3 4 using System; 5 using LinkedListLibrary; 6 7 namespace StackInheritanceLibrary 8 { 9 // class StackInheritance inherits class List's capabilities 10 public class StackInheritance : List 11 { 12 // pass name "stack" to List constructor 13 public StackInheritance() : base ( "stack" ) 14 { 15 } 16 17 // place dataValue at top of stack by inserting 18 // dataValue at front of linked list 19 public void Push( object dataValue ) 20 { 21 InsertAtFront( dataValue ); 22 } 23 24 // remove item from top of stack by removing 25 // item at front of linked list 26 public object Pop() 27 { 28 return RemoveFromFront(); 29 } 30 31 } // end class StackInheritance 32 } StackInheritance class is derived from List class Call InsertAtFront method of List class to push objects Call RemoveFromFront method of List class to pop objects

StackInheritanceTest.cs 1 // Fig. 23.11: StackInheritanceTest.cs 2 // Testing class StackInheritance. 3 4 using System; 5 using StackInheritanceLibrary; 6 using LinkedListLibrary; 7 8 namespace StackInheritanceTest 9 { 10 // demonstrate functionality of class StackInheritance 11 class StackInheritanceTest 12 { 13 static void Main( string [] args ) 14 { 15 StackInheritance stack = new StackInheritance(); 16 17 // create objects to store in the stack 18 bool aBoolean = true ; 19 char aCharacter = '$' ; 20 int anInteger = 34567 ; 21 string aString = "hello" ; 22 23 // use method Push to add items to stack 24 stack.Push( aBoolean ); 25 stack.Print(); 26 stack.Push( aCharacter ); 27 stack.Print(); 28 stack.Push( anInteger ); 29 stack.Print(); 30 stack.Push( aString ); 31 stack.Print(); 32 33 // use method Pop to remove items from stack 34 object removedObject = null ; 35 Create stack Create objects to store in stack Push objects onto the stack Print stack after each push

StackInheritanceTest.cs 36 // remove items from stack 37 try 38 { 39 while ( true ) 40 { 41 removedObject = stack.Pop(); 42 Console.WriteLine( removedObject + " popped" ); 43 stack.Print(); 44 } 45 } 46 47 // if exception occurs, print stack trace 48 catch ( EmptyListException emptyListException ) 49 { 50 Console.Error.WriteLine( 51 emptyListException.StackTrace ); 52 } 53 54 } // end method Main 55 56 } // end class StackInheritanceTest 57 } Remove objects from stack Empty stack exception

StackInheritanceTest.cs Program Output The stack is: True The stack is: $ True The stack is: 34567 $ True The stack is: hello 34567 $ True hello popped The stack is: 34567 $ True 34567 popped The stack is: $ True $ popped The stack is: True True popped Empty stack at LinkedListLibrary.List.RemoveFromFront() in z:\ch24\linkedlistlibrary\linkedlistlibrary.cs:line 114 at StackInheritanceLibrary.StackInheritance.Pop() in z:\ch24\stackinheritancelibrary\ stackinheritancelibrary.cs:line 28 at StackInheritanceTest.StackInheritanceTest.Main(String[] args in z:\ch24\fig24_11\stackinheritancetest.cs:line 41

StackCompositionLibrary.cs 1 // Fig. 23.12: StackCompositionLibrary.cs 2 // StackComposition definition with composed List object. 3 4 using System; 5 using LinkedListLibrary; 6 7 namespace StackCompositionLibrary 8 { 9 // class StackComposition encapsulates List's capabilities 10 public class StackComposition 11 { 12 private List stack; 13 14 // construct empty stack 15 public StackComposition() 16 { 17 stack = new List( "stack" ); 18 } 19 20 // add object to stack 21 public void Push( object dataValue ) 22 { 23 stack.InsertAtFront( dataValue ); 24 } 25 26 // remove object from stack 27 public object Pop() 28 { 29 return stack.RemoveFromFront(); 30 } 31 Create List object Call method InsertAtFront to push Use method RemoveFromFrontto pop

StackCompositionLibrary.cs 32 // determine whether stack is empty 33 public bool IsEmpty() 34 { 35 return stack.IsEmpty(); 36 } 37 38 // output stack contents 39 public void Print() 40 { 41 stack.Print(); 42 } 43 44 } // end class StackComposition 45 } Call is empty to see if list has nodes Call method Print for output

23.5 Queues First-in, first-out (FIFO) data structure Nodes removed from head, added to tail Operations: Enqueue: insert node Dequeue: remove node Many computer applications: Printer spooling Information packets on networks

QueueInheritanceLibrary.cs 1 // Fig. 23.13: QueueInheritanceLibrary.cs 2 // Implementing a queue by inheriting from class List. 3 4 using System; 5 using LinkedListLibrary; 6 7 namespace QueueInheritanceLibrary 8 { 9 // class QueueInheritance inherits List's capabilities 10 public class QueueInheritance : List 11 { 12 // pass name "queue" to List constructor 13 public QueueInheritance() : base ( "queue" ) 14 { 15 } 16 17 // place dataValue at end of queue by inserting 18 // dataValue at end of linked list 19 public void Enqueue( object dataValue ) 20 { 21 InsertAtBack( dataValue ); 22 } 23 24 // remove item from front of queue by removing 25 // item at front of linked list 26 public object Dequeue( ) 27 { 28 return RemoveFromFront(); 29 } 30 31 } // end of QueueInheritance 32 } Call InsertAtBack to enqueue Call RemoveFromFront to dequeue Class QueueInheritance derives from class List

QueueTest.cs 1 // Fig. 23.14: QueueTest.cs 2 // Testing class QueueInheritance. 3 4 using System; 5 using QueueInheritanceLibrary; 6 using LinkedListLibrary; 7 8 namespace QueueTest 9 { 10 // demonstrate functionality of class QueueInheritance 11 class QueueTest 12 { 13 static void Main( string [] args ) 14 { 15 QueueInheritance queue = new QueueInheritance(); 16 17 // create objects to store in the stack 18 bool aBoolean = true ; 19 char aCharacter = '$' ; 20 int anInteger = 34567 ; 21 string aString = "hello" ; 22 23 // use method Enqueue to add items to queue 24 queue.Enqueue( aBoolean ); 25 queue.Print(); 26 queue.Enqueue( aCharacter ); 27 queue.Print(); 28 queue.Enqueue( anInteger ); 29 queue.Print(); 30 queue.Enqueue( aString ); 31 queue.Print(); 32 33 // use method Dequeue to remove items from queue 34 object removedObject = null ; 35 Create queue Create objects to be inserted into queue Enqueue objects Print queue after each enqueue

QueueTest.cs 36 // remove items from queue 37 try 38 { 39 while ( true ) 40 { 41 removedObject = queue.Dequeue(); 42 Console.WriteLine( removedObject + " dequeue" ); 43 queue.Print(); 44 } 45 } 46 47 // if exception occurs, print stack trace 48 catch ( EmptyListException emptyListException ) 49 { 50 Console.Error.WriteLine( 51 emptyListException.StackTrace ); 52 } 53 54 } // end method Main 55 56 } // end class QueueTest 57 } Dequeue objects Print queue after each enqueue

QueueTest.cs Program Output The queue is: True The queue is: True $ The queue is: True $ 34567 The queue is: True $ 34567 hello True dequeue The queue is: $ 34567 hello $ dequeue The queue is: 34567 hello 34567 dequeue The queue is: hello hello dequeue Empty queue at LinkedListLibrary.List.RemoveFromFront() in z:\ch24\linkedlistlibrary\linkedlistlibrary.cs:line 114 at QueueInheritanceLibrary.QueueInheritance.Dequeue() in z:\ch24\queueinheritancelibrary\ queueinheritancelibrary.cs:line 28 at QueueTest.QueueTest.Main(String[] args) in z:\ch24\fig24_13\queuetest.cs:line 41

23.6 Trees Tree: non-linear, two-dimensional data sturcuture Binary tree: Contain two links Root node: first node in a tree Links refer to child nodes Node with no children is a leaf node Binary Search tree: Values in left subtree are less than the value of the subtree’s parent Values in right subtree are greater than the value of the subtree’s parent

23.6.1 Binary Search Tree of Integer Values Traversal: method of retrieving data from a tree In these methods if there is a subtree, recursively the traversal is called recursively Inorder traversal: Get data from left child of node Get data from node Get data from right child of node Preorder traversal: Get data from node Get data from left child of node Get data from right child of node

23.6.1 Binary Search Tree of Integer Values Postorder traversal Get data from left child of node Get data from right child of node Get data from node Level-order traversal Visit nodes of tree row by row, from left to right

23.6 Trees Fig. 23.15 A graphical representation of a binary tree. B A D C

23.6 Trees Fig. 23.16 A binary search tree containing 12 values. 47 25 77 11 7 17 65 93 68 43 31 44

BinaryTreeLibrary.cs 1 // Fig. 23.17: BinaryTreeLibrary.cs 2 // Definition of class TreeNode and class Tree. 3 4 using System; 5 6 namespace BinaryTreeLibrary 7 { 8 // class TreeNode definition 9 class TreeNode 10 { 11 private TreeNode leftNode; 12 private int data; 13 private TreeNode rightNode; 14 15 // initialize data and make this a leaf node 16 public TreeNode( int nodeData ) 17 { 18 data = nodeData; 19 leftNode = rightNode = null ; // node has no children 20 } 21 22 // LeftNode property 23 public TreeNode LeftNode 24 { 25 get 26 { 27 return leftNode; 28 } 29 30 set 31 { 32 leftNode = value; 33 } 34 } 35 Left and right subtree references Data stored in node Since new nodes are leaf, set subtree references to null Accessor methods for left subtree

BinaryTreeLibrary.cs 36 // Data property 37 public int Data 38 { 39 get 40 { 41 return data; 42 } 43 44 set 45 { 46 data = value; 47 } 48 } 49 50 // RightNode property 51 public TreeNode RightNode 52 { 53 get 54 { 55 return rightNode; 56 } 57 58 set 59 { 60 rightNode = value; 61 } 62 } 63 64 Accessor methods for nodes data Accessor methods for right subtree

BinaryTreeLibrary.cs 65 // insert TreeNode into Tree that contains nodes; 66 // ignore duplicate values 67 public void Insert( int insertValue ) 68 { 69 // insert in left subtree 70 if ( insertValue < data ) 71 { 72 // insert new TreeNode 73 if ( leftNode == null ) 74 leftNode = new TreeNode( insertValue ); 75 76 // continue traversing left subtree 77 else 78 leftNode.Insert( insertValue ); 79 } 80 81 // insert in right subtree 82 else if ( insertValue > data ) 83 { 84 // insert new TreeNode 85 if ( rightNode == null ) 86 rightNode = new TreeNode( insertValue ); 87 88 // continue traversing right subtree 89 else 90 rightNode.Insert( insertValue ); 91 } 92 93 } // end method Insert 94 95 } // end class TreeNode 96 Method to determine location of new node If value of new node is less than root, and the left subtree is empty, insert node as left child of root If left subtree is not empty, recursively call Insert to determine location of new node in subtree If value of new node is greater than root, and the right subtree is empty, insert node as right child of root If right subtree is not empty, recursively call Insert to determine location of new node in subtree

BinaryTreeLibrary.cs 97 // class Tree definition 98 public class Tree 99 { 100 private TreeNode root; 101 102 // construct an empty Tree of integers 103 public Tree() 104 { 105 root = null ; 106 } 107 108 // Insert a new node in the binary search tree. 109 // If the root node is null, create the root node here. 110 // Otherwise, call the insert method of class TreeNode. 111 public void InsertNode( int insertValue ) 112 { 113 lock ( this ) 114 { 115 if ( root == null ) 116 root = new TreeNode( insertValue ); 117 118 else 119 root.Insert( insertValue ); 120 } 121 } 122 123 // begin preorder traversal 124 public void PreorderTraversal() 125 { 126 lock ( this ) 127 { 128 PreorderHelper( root ); 129 } 130 } 131 Reference to root of tree Set root to null when tree first created Method to insert a new node into tree If tree is empty insert new node as root If tree is not empty call Insert to determine location of new node Perform preorder traversal Call PreorderHelper to help perform traversal

BinaryTreeLibrary.cs 132 // recursive method to perform preorder traversal 133 private void PreorderHelper( TreeNode node ) 134 { 135 if ( node == null ) 136 return ; 137 138 // output node data 139 Console.Write( node.Data + " " ); 140 141 // traverse left subtree 142 PreorderHelper( node.LeftNode ); 143 144 // traverse right subtree 145 PreorderHelper( node.RightNode ); 146 } 147 148 // begin inorder traversal 149 public void InorderTraversal() 150 { 151 lock ( this ) 152 { 153 InorderHelper( root ); 154 } 155 } 156 157 // recursive method to perform inorder traversal 158 private void InorderHelper( TreeNode node ) 159 { 160 if ( node == null ) 161 return ; 162 163 // traverse left subtree 164 InorderHelper( node.LeftNode ); 165 Method to help with preorder traversal Call PreorderHelper recursively on left subtree Display node data Call PreorderHelper recursively on right subtree Perform inorder traversal Call InorderHelper to help with traversal Method to help with inorder traversal Call InorderHelper recursively on left subtree

BinaryTreeLibrary.cs 166 // output node data 167 Console.Write( node.Data + " " ); 168 169 // traverse right subtree 170 InorderHelper( node.RightNode ); 171 } 172 173 // begin postorder traversal 174 public void PostorderTraversal() 175 { 176 lock ( this ) 177 { 178 PostorderHelper( root ); 179 } 180 } 181 182 // recursive method to perform postorder traversal 183 private void PostorderHelper( TreeNode node ) 184 { 185 if ( node == null ) 186 return ; 187 188 // traverse left subtree 189 PostorderHelper( node.LeftNode ); 190 191 // traverse right subtree 192 PostorderHelper( node.RightNode ); 193 194 // output node data 195 Console.Write( node.Data + " " ); 196 } 197 198 } // end class Tree 199 } Display node data Call InorderHelper recursively on right subtree Perform postorder traversal Call PostorderHelper to help with traversal Method to help with postorder traversal Call PostorderHelper recursively on left subtree Call PostorderHelper recursively on right subtree Display node data

TreeTest.cs 1 // Fig. 23.18: TreeTest.cs 2 // This program tests class Tree. 3 4 using System; 5 using BinaryTreeLibrary; 6 7 namespace TreeTest 8 { 9 // class TreeTest definition 10 public class TreeTest 11 { 12 // test class Tree 13 static void Main( string [] args ) 14 { 15 Tree tree = new Tree(); 16 int insertValue; 17 18 Console.WriteLine( "Inserting values: " ); 19 Random random = new Random(); 20 21 // insert 10 random integers from 0-99 in tree 22 for ( int i = 1 ; i <= 10 ; i++ ) 23 { 24 insertValue = random.Next( 100 ); 25 Console.Write( insertValue + " " ); 26 27 tree.InsertNode( insertValue ); 28 } 29 30 // perform preorder traveral of tree 31 Console.WriteLine( "\n\nPreorder traversal" ); 32 tree.PreorderTraversal(); 33 Create a tree Insert ten nodes in tree Call preorder traversal

TreeTest.cs Program Output 34 // perform inorder traveral of tree 35 Console.WriteLine( "\n\nInorder traversal" ); 36 tree.InorderTraversal(); 37 38 // perform postorder traveral of tree 39 Console.WriteLine( "\n\nPostorder traversal" ); 40 tree.PostorderTraversal(); 41 Console.WriteLine(); 42 } 43 44 } // end class TreeTest 45 } Inserting values: 39 69 94 47 50 72 55 41 97 73 Preorder traversal 39 69 47 41 50 55 94 72 73 97 Inorder traversal 39 41 47 50 55 69 72 73 94 97 Postorder traversal 41 55 50 47 73 72 97 94 69 39 Call inorder traversal Call postorder traversal

26.1 Binary Search Tree of Integer Values Fig. 23.19 A binary search tree. 27 13 42 6 33 48 17

23.6.2 Binary Search Tree of Icomparable Objects Can use polymorphism to manipulate objects of different types in uniform ways Binary search trees can be implemented to manipulate data of any object that implements the Icomparable interface

BinaryTreeLibrary2.cs 1 // Fig. 23.20: BinaryTreeLibrary2.cs 2 // Definition of class TreeNode and class Tree for IComparable 3 // objects. 4 5 using System; 6 7 namespace BinaryTreeLibrary2 8 { 9 // class TreeNode definition 10 class TreeNode 11 { 12 private TreeNode leftNode; 13 private IComparable data; 14 private TreeNode rightNode; 15 16 // initialize data and make this a leaf node 17 public TreeNode( IComparable nodeData ) 18 { 19 data = nodeData; 20 leftNode = rightNode = null ; // node has no children 21 } 22 23 // LeftNode property 24 public TreeNode LeftNode 25 { 26 get 27 { 28 return leftNode; 29 } 30 31 set 32 { 33 leftNode = value; 34 } 35 }

BinaryTreeLibrary2.cs 36 37 // Data property 38 public IComparable Data 39 { 40 get 41 { 42 return data; 43 } 44 45 set 46 { 47 data = value; 48 } 49 } 50 51 // RightNode property 52 public TreeNode RightNode 53 { 54 get 55 { 56 return rightNode; 57 } 58 59 set 60 { 61 rightNode = value; 62 } 63 } 64

BinaryTreeLibrary2.cs 65 // insert TreeNode into Tree that contains nodes; 66 // ignore duplicate values 67 public void Insert( IComparable insertValue ) 68 { 69 // insert in left subtree 70 if ( insertValue.CompareTo( data ) < 0 ) 71 { 72 // insert new TreeNode 73 if ( leftNode == null ) 74 leftNode = new TreeNode( insertValue ); 75 76 // continue traversing left subtree 77 else 78 leftNode.Insert( insertValue ); 79 } 80 81 // insert in right subtree 82 else if ( insertValue.CompareTo( data ) > 0 ) 83 { 84 // insert new TreeNode 85 if ( rightNode == null ) 86 rightNode = new TreeNode( insertValue ); 87 88 // continue traversing right subtree 89 else 90 rightNode.Insert( insertValue ); 91 } 92 93 } // end method Insert 94 95 } // end class TreeNode 96 Use Icomparable’s method CompareTo to determine if new node is less than its parent Use Icomparable’s method CompareTo to determine if new node is greater than its parent

BinaryTreeLibrary2.cs 97 // class Tree definition 98 public class Tree 99 { 100 private TreeNode root; 101 102 // construct an empty Tree of integers 103 public Tree() 104 { 105 root = null ; 106 } 107 108 // Insert a new node in the binary search tree. 109 // If the root node is null, create the root node here. 110 // Otherwise, call the insert method of class TreeNode. 111 public void InsertNode( IComparable insertValue ) 112 { 113 lock ( this ) 114 { 115 if ( root == null ) 116 root = new TreeNode( insertValue ); 117 118 else 119 root.Insert( insertValue ); 120 } 121 } 122 123 // begin preorder traversal 124 public void PreorderTraversal() 125 { 126 lock ( this ) 127 { 128 PreorderHelper( root ); 129 } 130 } 131

BinaryTreeLibrary2.cs 132 // recursive method to perform preorder traversal 133 private void PreorderHelper( TreeNode node ) 134 { 135 if ( node == null ) 136 return ; 137 138 // output node data 139 Console.Write( node.Data + " " ); 140 141 // traverse left subtree 142 PreorderHelper( node.LeftNode ); 143 144 // traverse right subtree 145 PreorderHelper( node.RightNode ); 146 } 147 148 // begin inorder traversal 149 public void InorderTraversal() 150 { 151 lock ( this ) 152 { 153 InorderHelper( root ); 154 } 155 } 156 157 // recursive method to perform inorder traversal 158 private void InorderHelper( TreeNode node ) 159 { 160 if ( node == null ) 161 return ; 162 163 // traverse left subtree 164 InorderHelper( node.LeftNode ); 165

BinaryTreeLibrary2.cs 166 // output node data 167 Console.Write( node.Data + " " ); 168 169 // traverse right subtree 170 InorderHelper( node.RightNode ); 171 } 172 173 // begin postorder traversal 174 public void PostorderTraversal() 175 { 176 lock ( this ) 177 { 178 PostorderHelper( root ); 179 } 180 } 181 182 // recursive method to perform postorder traversal 183 private void PostorderHelper( TreeNode node ) 184 { 185 if ( node == null ) 186 return ; 187 188 // traverse left subtree 189 PostorderHelper( node.LeftNode ); 190 191 // traverse right subtree 192 PostorderHelper( node.RightNode ); 193 194 // output node data 195 Console.Write( node.Data + " " ); 196 } 197 198 } // end class Tree 199 }

TreeTest.cs 1 // Fig. 23.21: TreeTest.cs 2 // This program tests class Tree. 3 4 using System; 5 using BinaryTreeLibrary2; 6 7 namespace TreeTest 8 { 9 // class TreeTest definition 10 public class TreeTest 11 { 12 // test class Tree 13 static void Main( string [] args ) 14 { 15 int [] intArray = { 8 , 2 , 4 , 3 , 1 , 7 , 5 , 6 }; 16 double [] doubleArray = 17 { 8.8 , 2.2 , 4.4 , 3.3 , 1.1 , 7.7 , 5.5 , 6.6 }; 18 string [] stringArray = { "eight" , "two" , "four" , 19 "three" , "one" , "seven" , "five" , "six" }; 20 21 // create int Tree 22 Tree intTree = new Tree(); 23 populateTree( intArray, intTree, "intTree" ); 24 traverseTree( intTree, "intTree" ); 25 26 // create double Tree 27 Tree doubleTree = new Tree(); 28 populateTree( doubleArray, doubleTree, "doubleTree" ); 29 traverseTree( doubleTree, "doubleTree" ); 30 31 // create string Tree 32 Tree stringTree = new Tree(); 33 populateTree( stringArray, stringTree, "stringTree" ); 34 traverseTree( stringTree, "stringTree" ); 35 } Populate trees with int, double and string values

TreeTest.cs 36 37 // populate Tree with array elements 38 static void populateTree( 39 Array array, Tree tree, string name ) 40 { 41 Console.WriteLine( "\nInserting into " + name + ":" ); 42 43 foreach ( IComparable data in array ) 44 { 45 Console.Write( data + " " ); 46 tree.InsertNode( data ); 47 } 48 } 49 50 // insert perform traversals 51 static void traverseTree( Tree tree, string treeType ) 52 { 53 // perform preorder traveral of tree 54 Console.WriteLine( 55 "\n\nPreorder traversal of " + treeType ); 56 tree.PreorderTraversal(); 57 58 // perform inorder traveral of tree 59 Console.WriteLine( 60 "\n\nInorder traversal of " + treeType ); 61 tree.InorderTraversal(); 62 Method to add data from arrays to trees Insert nodes into tree Method to traverse tree Perform preorder traversal Perform inorder traversal

TreeTest.cs Program Output 63 // perform postorder traveral of tree 64 Console.WriteLine( 65 "\n\nPostorder traversal of " + treeType ); 66 tree.PostorderTraversal(); 67 Console.WriteLine( "\n" ); 68 } 69 70 } // end class TreeTest 71 } Inserting into intTree: 8 2 4 3 1 7 5 6 Preorder traversal of intTree 8 2 1 4 3 7 5 6 Inorder traversal of intTree 1 2 3 4 5 6 7 8 Postorder traversal of intTree 1 3 6 5 7 4 2 8 Perform postorder traversal

TreeTest.cs Program Output Inserting into doubleTree: 8.8 2.2 4.4 3.3 1.1 7.7 5.5 6.6 Preorder traversal of doubleTree 8.8 2.2 1.1 4.4 3.3 7.7 5.5 6.6 Inorder traversal of doubleTree 1.1 2.2 3.3 4.4 5.5 6.6 7.7 8.8 Postorder traversal of doubleTree 1.1 3.3 6.6 5.5 7.7 4.4 2.2 8.8 Inserting into stringTree: eight two four three one seven five six Preorder traversal of stringTree eight two four five three one seven six Inorder traversal of stringTree eight five four one seven six three two Postorder traversal of stringTree five six seven one three four two eight

23.7 Collection Class Collection classes: Prepackaged data structures Store collections of data Programmer uses already existing data structures

23.7.1 Class Array Properties: Length: returns length of array Reverse: can reverse elements of entire or part of an array Sort: sorts an array Copy: copies one array into another array BinarySearch: searches an array for a specified value Clear: removes all elements from an array CreateInstance: create a new array of a specified type LastIndexOf: returns index of last occurrence of an object

UsingArray.cs 1 // Fig. 23.22: UsingArray.cs 2 // Using Array class to perform common array manipulations. 3 4 using System; 5 using System.Windows.Forms; 6 using System.Collections; 7 8 namespace UsingArray 9 { 10 // demonstrate algorithms of class Array 11 class UsingArray 12 { 13 private int [] intValues = { 1 , 2 , 3 , 4 , 5 , 6 }; 14 private double [] doubleValues = 15 { 8.4 , 9.3 , 0.2 , 7.9 , 3.4 }; 16 private int [] intValuesCopy; 17 private string output; 18 19 // method to build and display program output 20 public void Start() 21 { 22 intValuesCopy = new int [ intValues.Length ]; 23 24 output = "Initial array values:\n" ; 25 PrintArray(); // output initial array contents 26 27 // sort doubleValues 28 Array.Sort( doubleValues ); 29 30 // copy intValues into intValuesCopy 31 Array.Copy( intValues, intValuesCopy, 32 intValues.Length ); 33 Sort array in ascending order Copy values from one array to another array

UsingArray.cs 34 output += "\nArray values after Sort and Copy:\n" ; 35 PrintArray(); // output array contents 36 output += "\n" ; 37 38 // search for 5 in intValues 39 int result = Array.BinarySearch( intValues, 5 ); 40 output += 41 ( result >= 0 ? "5 found at element " + result : 42 "5 not found" ) + " in intValues\n" ; 43 44 // search for 8763 in intValues 45 result = Array.BinarySearch( intValues, 8763 ); 46 output += 47 ( result >= 0 ? "8763 found at element " + result : 48 "8763 not found" ) + " in intValues" ; 49 50 MessageBox.Show( output, "Using Class Array" , 51 MessageBoxButtons. OK , MessageBoxIcon. Information ); 52 } 53 54 // append array content to output string 55 private void PrintArray() 56 { 57 output += "doubleValues: " ; 58 59 foreach ( double element in doubleValues ) 60 output += element + " " ; 61 62 output += "\nintValues: " ; 63 64 foreach ( int element in intValues ) 65 output += element + " " ; 66 67 output += "\nintValuesCopy: " ; 68 Search sorted array for parameter passed

UsingArray.cs Program Output 69 foreach ( int element in intValuesCopy ) 70 output += element + " " ; 71 72 output += "\n" ; 73 } 74 75 // main entry point for application 76 static void Main( string [] args ) 77 { 78 UsingArray application = new UsingArray(); 79 80 application.Start(); 81 } 82 83 } // end class UsingArray 84 }

23.7.2 Class ArrayList Arrays have a fixed size Provides functionality of array, but can be resized dynamically Property Capacity: Contains number of elements an array can hold Can be doubled if array needs to grow

ArrayListTest.cs 1 // Fig. 23.24: ArrayListTest.cs 2 // Using class ArrayList. 3 4 using System; 5 using System.Drawing; 6 using System.Collections; 7 using System.ComponentModel; 8 using System.Windows.Forms; 9 using System.Data; 10 using System.Text; 11 12 namespace ArrayListTest 13 { 14 // demonstrating ArrayList functionality 15 public class ArrayListTest : System.Windows.Forms.Form 16 { 17 private System.Windows.Forms.Button addButton; 18 private System.Windows.Forms.TextBox inputTextBox; 19 private System.Windows.Forms.Label inputLabel; 20 private System.Windows.Forms.Button removeButton; 21 private System.Windows.Forms.Button firstButton; 22 private System.Windows.Forms.Button lastButton; 23 private System.Windows.Forms.Button isEmptyButton; 24 private System.Windows.Forms.Button containsButton; 25 private System.Windows.Forms.Button locationButton; 26 private System.Windows.Forms.Button trimButton; 27 private System.Windows.Forms.Button statisticsButton; 28 private System.Windows.Forms.Button displayButton; 29 30 // Required designer variable. 31 private System.ComponentModel.Container components = null ; 32 private System.Windows.Forms.TextBox consoleTextBox; 33 34 // ArrayList for manipulating strings 35 private ArrayList arrayList = new ArrayList( 1 ); Create an array list of one element

ArrayListTest.cs 36 37 public ArrayListTest() 38 { 39 // Required for Windows Form Designer support 40 InitializeComponent(); 41 } 42 43 // Visual Studio.NET generated code 44 45 // main entry point for the application 46 [STAThread] 47 static void Main() 48 { 49 Application.Run( new ArrayListTest() ); 50 } 51 52 // add item to end of arrayList 53 private void addButton_Click( 54 object sender, System.EventArgs e ) 55 { 56 arrayList.Add( inputTextBox.Text ); 57 consoleTextBox.Text = 58 "Added to end: " + inputTextBox.Text; 59 inputTextBox.Clear(); 60 } 61 62 // remove specified item from arrayList 63 private void removeButton_Click( 64 object sender, System.EventArgs e ) 65 { 66 arrayList.Remove( inputTextBox.Text ); 67 consoleTextBox.Text = "Removed: " + inputTextBox.Text; 68 inputTextBox.Clear(); 69 } 70 Call method add to add an element to arrayList Method to add an element to arrayList when user clicks add button Method to remove an object when user clicks button Call method remove to remove object

ArrayListTest.cs 71 // display first element 72 private void firstButton_Click( 73 object sender, System.EventArgs e ) 74 { 75 // get first element 76 try 77 { 78 consoleTextBox.Text = 79 "First element: " + arrayList[ 0 ]; 80 } 81 82 // show exception if no elements in arrrayList 83 catch ( ArgumentOutOfRangeException outOfRange ) 84 { 85 consoleTextBox.Text = outOfRange.ToString(); 86 } 87 } 88 89 // display last element 90 private void lastButton_Click( 91 object sender, System.EventArgs e ) 92 { 93 // get last element 94 try 95 { 96 consoleTextBox.Text = "Last element: " + 97 arrayList[ arrayList.Count - 1 ]; 98 } 99 100 // show exception if no elements in arrrayList 101 catch ( ArgumentOutOfRangeException outOfRange ) 102 { 103 consoleTextBox.Text = outOfRange.ToString(); 104 } 105 } Display last element when user clicks button Get last element in arrayList Display first element when user clicks button

ArrayListTest.cs 106 107 // determine whether arrayList is empty 108 private void isEmptyButton_Click( 109 object sender, System.EventArgs e ) 110 { 111 consoleTextBox.Text = ( arrayList.Count == 0 ? 112 "arrayList is empty" : "arrayList is not empty" ); 113 } 114 115 // determine whether arrayList contains specified object 116 private void containsButton_Click( 117 object sender, System.EventArgs e ) 118 { 119 if ( arrayList.Contains( inputTextBox.Text ) ) 120 consoleTextBox.Text = "arrayList contains " + 121 inputTextBox.Text; 122 else 123 consoleTextBox.Text = inputTextBox.Text + 124 " not found" ; 125 } 126 127 // determine location of specified object 128 private void locationButton_Click( 129 object sender, System.EventArgs e ) 130 { 131 consoleTextBox.Text = "Element is at location " + 132 arrayList.IndexOf( inputTextBox.Text ); 133 } 134 Test if array is empty Method to determine if object is in arrayList when user clicks button Test if object is in arrayList Method to determine index of specified object when user clicks button Determine index of object

ArrayListTest.cs 135 // trim arrayList to current size 136 private void trimButton_Click( 137 object sender, System.EventArgs e ) 138 { 139 arrayList.TrimToSize(); 140 consoleTextBox.Text = "Vector trimmed to size" ; 141 } 142 143 // show arrayList current size and capacity 144 private void statisticsButton_Click( 145 object sender, System.EventArgs e ) 146 { 147 consoleTextBox.Text = "Size = " + arrayList.Count + 148 "; capacity = " + arrayList.Capacity; 149 } 150 151 // display contents of arrayList 152 private void displayButton_Click( 153 object sender, System.EventArgs e ) 154 { 155 IEnumerator enumerator = arrayList.GetEnumerator(); 156 StringBuilder buffer = new StringBuilder(); 157 158 while ( enumerator.MoveNext() ) 159 buffer.Append( enumerator.Current + " " ); 160 161 consoleTextBox.Text = buffer.ToString(); 162 } 163 } 164 } Method to reduce size to capacity when button clicked Call TrimToSize to reduce size of arrayList to number of elements in arrayList Display capacity and size or arrayList when button clicked Method to display elements when button clicked Create enumerator for traversal Use enumerator to traverse arrayList and output contents to buffer Display contents of buffer

ArrayListTest.cs Program Output

23.25 Class Stack Implements stack data structure

StackTest.cs 1 // Fig. 23.25: StackTest.cs 2 // Demonstrates class Stack of namespace System.Collections. 3 4 using System; 5 using System.Drawing; 6 using System.Collections; 7 using System.ComponentModel; 8 using System.Windows.Forms; 9 using System.Data; 10 using System.Text; 11 12 namespace StackTest 13 { 14 // demonstrate Stack collection 15 public class StackTest : System.Windows.Forms.Form 16 { 17 private System.Windows.Forms.Label inputLabel; 18 private System.Windows.Forms.TextBox inputTextBox; 19 private System.Windows.Forms.Button pushButton; 20 private System.Windows.Forms.Button popButton; 21 private System.Windows.Forms.Button peekButton; 22 private System.Windows.Forms.Button isEmptyButton; 23 private System.Windows.Forms.Button searchButton; 24 private System.Windows.Forms.Button displayButton; 25 private System.Windows.Forms.Label statusLabel; 26 27 // Required designer variable. 28 private System.ComponentModel.Container components = null ; 29 30 private Stack stack; 31 32 public StackTest() 33 { 34 // Required for Windows Form Designer support 35 InitializeComponent();

StackTest.cs 36 37 // create Stack 38 stack = new Stack(); 39 } 40 41 // Visual Studio.NET generated code 42 43 // main entry point for the application 44 [STAThread] 45 static void Main() 46 { 47 Application.Run( new StackTest() ); 48 } 49 50 // push element onto stack 51 private void pushButton_Click( 52 object sender, System.EventArgs e ) 53 { 54 stack.Push( inputTextBox.Text ); 55 statusLabel.Text = "Pushed: " + inputTextBox.Text; 56 } 57 58 // pop element from stack 59 private void popButton_Click( 60 object sender, System.EventArgs e ) 61 { 62 // pop element 63 try 64 { 65 statusLabel.Text = "Popped: " + stack.Pop(); 66 } 67 Create new stack Insert specified object into stack when user clicks button Invoke method push to insert object Remove top element from stack when user clicks button Call method pop to remove item

StackTest.cs 68 // print message if stack is empty 69 catch ( InvalidOperationException invalidOperation ) 70 { 71 statusLabel.Text = invalidOperation.ToString(); 72 } 73 } 74 75 // peek at top element of stack 76 private void peekButton_Click( 77 object sender, System.EventArgs e ) 78 { 79 // view top element 80 try 81 { 82 statusLabel.Text = "Top: " + stack.Peek(); 83 } 84 85 // print message if stack is empty 86 catch ( InvalidOperationException invalidOperation ) 87 { 88 statusLabel.Text = invalidOperation.ToString(); 89 } 90 } 91 92 // determine whether stack is empty 93 private void isEmptyButton_Click( 94 object sender, System.EventArgs e ) 95 { 96 statusLabel.Text = ( stack.Count == 0 ? 97 "Stack is empty" : "Stack is not empty" ); 98 } 99 Method to return top object in stack without returning it when user clicks button Call method Peek to view top object Method to test if stack is empty Determine if stack is empty

StackTest.cs 100 // determine whether specified element is on stack 101 private void searchButton_Click( 102 object sender, System.EventArgs e ) 103 { 1 04 string result = stack.Contains( inputTextBox.Text ) ? 105 " found" : " not found" ; 106 107 statusLabel.Text = inputTextBox.Text + result; 108 } 109 110 // display stack contents 111 private void displayButton_Click( 112 object sender, System.EventArgs e ) 113 { 114 IEnumerator enumerator = stack.GetEnumerator(); 115 StringBuilder buffer = new StringBuilder(); 116 117 // while the enumerator can move on to the next element 118 // print that element out. 119 while ( enumerator.MoveNext() ) 120 buffer.Append( enumerator.Current + " " ); 121 122 statusLabel.Text = buffer.ToString(); 123 } 124 } 125 } Search stack for specified object Determine if object is in stack

23.7.4 Class Hashtable Hashing: Convert a key into a subscript and store information at that index of an array Use same key for retrieval of information Collisions: When two different objects hash to the same subscript Can hash again Can store second object in next open cell Each cell can be a linked list that contains all objects that hash to its subscript Load factor: ratio of number of objects in hash table to the size of the hash table

23.7.4 Class Hashtable Class Hashtable provides functionality of hash tables without knowing how they work Hash function: determines where to place data in a hash table

HashtableTest.cs 1 // Fig. 23.26: HashtableTest.cs 2 // Demonstrate class Hashtable of namespace System.Collections. 3 4 using System; 5 using System.Drawing; 6 using System.Collections; 7 using System.ComponentModel; 8 using System.Windows.Forms; 9 using System.Data; 10 using System.Text; 11 12 namespace HashTableTest 13 { 14 // demonstrate Hashtable functionality 15 public class HashTableTest : System.Windows.Forms.Form 16 { 17 private System.Windows.Forms.Label firstNameLabel; 18 private System.Windows.Forms.Label lastNameLabel; 19 private System.Windows.Forms.Button addButton; 20 private System.Windows.Forms.TextBox lastNameTextBox; 21 private System.Windows.Forms.TextBox consoleTextBox; 22 private System.Windows.Forms.TextBox firstNameTextBox; 23 private System.Windows.Forms.Button getButton; 24 private System.Windows.Forms.Button removeButton; 25 private System.Windows.Forms.Button emptyButton; 26 private System.Windows.Forms.Button containsKeyButton; 27 private System.Windows.Forms.Button clearTableButton; 28 private System.Windows.Forms.Button listObjectsButton; 29 private System.Windows.Forms.Button listKeysButton; 30 private System.Windows.Forms.Label statusLabel; 31 32 // Required designer variable. 33 private System.ComponentModel.Container components = null ; 34

HashtableTest.cs 35 // Hashtable to demonstrate functionality 36 private Hashtable table; 37 38 public HashTableTest() 39 { 40 // Required for Windows Form Designer support 41 InitializeComponent(); 42 43 // create Hashtable object 44 table = new Hashtable(); 45 } 46 47 // Visual Studio.NET generated code 48 49 // main entry point for the application 50 [STAThread] 51 static void Main() 52 { 53 Application.Run( new HashTableTest() ); 54 } 55 56 // add last name and Employee object to table 57 private void addButton_Click( 58 object sender, System.EventArgs e ) 59 { 60 Employee employee = new Employee( firstNameTextBox.Text, 61 lastNameTextBox.Text ); 62 63 // add new key/value pair 64 try 65 { 66 table.Add( lastNameTextBox.Text, employee ); 67 statusLabel.Text = "Put: " + employee.ToString(); 68 } 69 Add new person to table when button clicked Add employee object to the table using last name as a hash key

HashtableTest.cs 70 // if key is null or already in table, output message 71 catch ( ArgumentException argumentException ) 72 { 73 statusLabel.Text = argumentException.ToString(); 74 } 75 } 76 77 // get object for given key 78 private void getButton_Click( 79 object sender, System.EventArgs e ) 80 { 81 object result = table[ lastNameTextBox.Text ]; 82 83 if ( result != null ) 84 statusLabel.Text = "Get: " + result.ToString(); 85 else 86 statusLabel.Text = "Get: " + lastNameTextBox.Text + 87 " not in table" ; 88 } 89 90 // remove key/value pair from table 91 private void removeButton_Click( 92 object sender, System.EventArgs e ) 93 { 94 table.Remove( lastNameTextBox.Text ); 95 statusLabel.Text = "Object Removed" ; 96 } 97 98 // determine whether table is empty 99 private void emptyButton_Click( 100 object sender, System.EventArgs e ) 101 { 102 statusLabel.Text = "Table is " + ( 103 table.Count == 0 ? "empty" : "not empty" ); 104 } Method to get object associated with specified key when user clicks button Retrieve object associated with key Method to remove a specified key and object from the hash table Remove object by invoking method Remove Method to determine if table is empty when user clicks button Determine if table is empty

HashtableTest.cs 105 106 // determine whether table contains specified key 107 private void containsKeyButton_Click( 108 object sender, System.EventArgs e ) 109 { 110 statusLabel.Text = "Contains key: " + 111 table.ContainsKey( lastNameTextBox.Text ); 112 } 113 114 // discard all table contents 115 private void clearTableButton_Click( 116 object sender, System.EventArgs e ) 117 { 118 table.Clear(); 119 statusLabel.Text = "Clear: Table is now empty" ; 120 } 121 122 // display list of objects in table 123 private void listObjectsButton_Click( 124 object sender, System.EventArgs e ) 125 { 126 IDictionaryEnumerator enumerator = 127 table.GetEnumerator(); 128 StringBuilder buffer = new StringBuilder(); 129 130 while ( enumerator.MoveNext() ) 131 buffer.Append( enumerator.Value + "\r\n" ); 132 133 consoleTextBox.Text = buffer.ToString(); 134 } 135 When user clicks button, determine if specified key is in hash table Invoke method ContainsKey to determine if key is in table Delete all objects from table when user clicks Use enumerator to output objects in hashtable

HashtableTest.cs 136 // display list of keys in table 137 private void listKeysButton_Click( 138 object sender, System.EventArgs e ) 139 { 140 IDictionaryEnumerator enumerator = 141 table.GetEnumerator(); 142 StringBuilder buffer = new StringBuilder(); 143 144 while ( enumerator.MoveNext() ) 145 buffer.Append( enumerator.Key + "\r\n" ); 146 147 consoleTextBox.Text = buffer.ToString(); 148 } 149 150 } // end class HashtableTest 151 152 // class Employee for use with HashtableTest 153 class Employee 154 { 155 private string first, last; 156 157 // constructor 158 public Employee( string fName, string lName ) 159 { 160 first = fName; 161 last = lName; 162 } 163 Use enumerator to display keys of hash table

HashtableTest.cs Program Output 164 // return Employee first and last names as string 165 public override string ToString() 166 { 167 return first + " " + last; 168 } 169 170 } // end class Employee 171 }

HashtableTest.cs Program Output

Csphtp1 23

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