Built-In Collection Classes
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Built-In Collection Classes |
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Hash Tables |
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Introduction |
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If you have been playing a little deeper with Microsoft Windows for a while, you are probably familiar with objects referred to as initialization files or ini files. These are files whose contents are made of lines that each displays a combination of a right value assigned to a left value. Here is an example: PROJECT=AIOCPE MANUFACTURER=HP Wrapper=1 DEFAULT=1 LOG_DISABLED=0 LOG_ERROR=1 LOG_WARNING=2 LOG_MAINTRACE=4 LOG_DETAILEDTRACE=8 FILESIZE=524288 |
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A hash table is list of items that each (item) is made of a right object assigned to a left object. The object on the left side is called a key. The object on the right side is called a value. Based on this, an item of a hash table is in the form: Key=Value Most hash tables are made of string keys and string values but the key or the value can also be a number or a more complex item. There is no strict rule as to what you use a hash table for. When you create one, it is up to you to decide what you want to do with it.
The .NET Framework supports hash tables at different levels but probably the most common class used is called Hashtable. The Hashtable class implements the ISerializable interface (that makes it possible for the list to be serialized(, the ICollection interface (used to keep track of the number of items in the list), and the IEnumerable interface (that would allow you to use the foreach loop). Before using a hash table, you can declare a variable of type Hashtable using one of its constructors such as the default one. Here is an example: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
return 0;
}
}
}
In this case, the primary list would be empty. To add an item to the list, you can call the Add() method. Its syntax is: public virtual void Add(object Key, object Value); As you can see, you must provide the key and the value as the first and second arguments to the method. Here are examples of calling the Add() method: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
Chelsea20062007.Add("Michael", "Ballack");
Chelsea20062007.Add("Didier", "Drogba");
return 0;
}
}
}
When calling the Add() method, you must provide a valid Key argument: it cannot be null. For example, the following code would produce an error: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
Chelsea20062007.Add("Michael", "Ballack");
Chelsea20062007.Add("Didier", "Drogba");
Chelsea20062007.Add(null, "Essien");
return 0;
}
}
}
This would produce: Unhandled Exception: System.ArgumentNullException: Key cannot be null. When adding the items to the list, each key must be unique: you cannot have two exact keys. If you try adding a key that exists already in the list, the compiler would throw an ArgumentException exception. Based on this, the following code would not work because, on the third call, a "Michael" key exists already: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
Chelsea20062007.Add("Michael", "Ballack");
Chelsea20062007.Add("Didier", "Drogba");
Chelsea20062007.Add("Michael", "Essien");
return 0;
}
}
}
This would produce: Unhandled Exception: System.ArgumentException: Item has already been added. Key in dictionary: 'Michael' Key being added: 'Michael' Besides the Add() method, you can use the indexed property of the Hashtable class to add an item to the list. To do this, enter the Key in the square brackets of the property and assign it the desired Value. Here is an example: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
Chelsea20062007.Add("Michael", "Ballack");
Chelsea20062007.Add("Didier", "Drogba");
Chelsea20062007["Claude"] = "Makelele";
return 0;
}
}
}
After adding one or more items to the list, they are stored in two collections. The keys are stored in a collection represented by a property named Keys. The values are stored in the Values property. Each of these properties is of type ICollection. Although, or because, the key and value are distinct, to consider their combination as a single object, the .NET Framework provides the DictionaryEntry structure. To access an item, you can use the foreach loop to visit each item. To support the foreach loop, the Hashtable class implements the IEnumerable.GetEnumerator() method. In this case, the item is of type DictionaryEntry: it contains a Key and a Value in combination. The DictionaryEntry structure contains two properties named Key and Value to identify the components of a combination. Here is an example: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
Chelsea20062007.Add("Michael", "Ballack");
Chelsea20062007.Add("Didier", "Drogba");
Chelsea20062007["Claude"] = "Makelele";
foreach (DictionaryEntry entry in Chelsea20062007)
Console.WriteLine("{0} {1}", entry.Key, entry.Value);
Console.WriteLine();
return 0;
}
}
}
This would produce: Didier Drogba Michael Ballack Claude Makelele Press any key to continue . . .
Locating an item in a hash table consists of looking for either a key, a value, or a combination of Key=Value. The Hashtable class is equipped to handle these operations with little effort on your part. If you know the key of an item but want to find a value, you can use the index property because it produces it. Here is an example: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
Chelsea20062007.Add("Michael", "Ballack");
Chelsea20062007.Add("Didier", "Drogba");
Chelsea20062007["Claude"] = "Makelele";
string Value = (string)Chelsea20062007["Didier"];
Console.WriteLine("The value of the Didier key is {0}",
Value);
Console.WriteLine();
return 0;
}
}
}
This would produce: The value of the Didier key is Drogba Press any key to continue . . . To find out whether a Key=Value item exists in the list, you can call the Contains() method. Its syntax is: public virtual bool Contains(object key); To look for an item, you pass its key as argument to this method. Here is an example: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
Chelsea20062007.Add("Michael", "Ballack");
Chelsea20062007.Add("Didier", "Drogba");
Chelsea20062007["Claude"] = "Makelele";
Console.WriteLine("List of items");
foreach (DictionaryEntry entry in Chelsea20062007)
Console.WriteLine("{0} {1}", entry.Key, entry.Value);
bool found = Chelsea20062007.Contains("Claude");
if (found == true)
Console.WriteLine("\nThe list contains an item " +
"whose key is Claude");
else
Console.WriteLine("\nThe list doesn't contain an " +
"item whose key is Claude");
found = Chelsea20062007.Contains("James");
if (found == true)
Console.WriteLine("\nThe list contains an item " +
"whose key is Claude");
else
Console.WriteLine("\nThe list doesn't contain an " +
"item whose key is James");
Console.WriteLine();
return 0;
}
}
}
This would produce: List of items Didier Drogba Michael Ballack Claude Makelele The list contains an item whose key is Claude The list doesn't contain an item whose key is James Press any key to continue . . . To find out whether a particular key exists in the list, you can call the ContainsKey() method whose syntax is: public virtual bool ContainsKey(object key); To find out whether a particular key exists in the list, you can call the ContainsKey() method whose syntax is: public virtual bool ContainsValue(object key); When calling this method, pass a Value value as argument. Here is an example: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
Chelsea20062007.Add("Michael", "Ballack");
Chelsea20062007.Add("Didier", "Drogba");
Chelsea20062007["Claude"] = "Makelele";
Console.WriteLine("List of items");
foreach (DictionaryEntry entry in Chelsea20062007)
Console.WriteLine("{0} {1}", entry.Key, entry.Value);
bool found = Chelsea20062007.ContainsValue("Makelele");
if (found == true)
Console.WriteLine("\nMakelele plays for Chelsea");
else
Console.WriteLine("\nMakelele doesn't plays for Chelsea");
found = Chelsea20062007.ContainsValue("Fortune");
if (found == true)
Console.WriteLine("\nRonaldinho plays for Chelsea");
else
Console.WriteLine("\nRonaldinho doesn't plays for Chelsea");
Console.WriteLine();
return 0;
}
}
}
This would produce: List of items Didier Drogba Michael Ballack Claude Makelele Makele plays for Chelsea Ronaldinho doesn't plays for Chelsea Press any key to continue . . .
To delete one item from the list, you can call the Remove() method. Its syntax is: public virtual void Remove(object key); Here is an example: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
Chelsea20062007.Add("Michael", "Ballack");
Chelsea20062007.Add("Didier", "Drogba");
Chelsea20062007["Claude"] = "Makelele";
Console.WriteLine("List of items");
foreach (DictionaryEntry entry in Chelsea20062007)
Console.WriteLine("{0} {1}", entry.Key, entry.Value);
Chelsea20062007.Remove("Didier");
Console.WriteLine("\nThe item that contains " +
"Didier has been removed\n");
Console.WriteLine("List of items");
foreach (DictionaryEntry entry in Chelsea20062007)
Console.WriteLine("{0} {1}", entry.Key, entry.Value);
Console.WriteLine();
return 0;
}
}
}
This would produce: List of items Didier Drogba Michael Ballack Claude Makelele The item that contains Didier has been removed List of items Michael Ballack Claude Makelele Press any key to continue . . . To delete all items from the list, you can call the Clear() method. Its syntax is: public virtual void Clear(); This is an example: using System;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
static int Main(string[] args)
{
Hashtable Chelsea20062007 = new Hashtable();
Chelsea20062007.Add("Michael", "Ballack");
Chelsea20062007.Add("Didier", "Drogba");
Chelsea20062007["Claude"] = "Makelele";
Console.WriteLine("List of items");
foreach (DictionaryEntry entry in Chelsea20062007)
Console.WriteLine("{0} {1}", entry.Key, entry.Value);
Chelsea20062007.Clear();
Console.WriteLine("\nThe list is now empty!");
Console.WriteLine("List of items");
foreach (DictionaryEntry entry in Chelsea20062007)
Console.WriteLine("{0} {1}", entry.Key, entry.Value);
Console.WriteLine();
return 0;
}
}
}
This would produce: List of items Didier Drogba Michael Ballack Claude Makelele The list is now empty! List of items Press any key to continue . . .
A stack is a technique of creating a list so that the last item added to the list is also the first one that can be removed. It can be illustrated as placing a few cups in a box that can receive only one on top of another (no adjacent cup). When it comes time to get one of those cups, you must first access the last one that was added. This technique of building a list is referred to as first-in last-out (FILO). To support stack types of collections, the .NET Framework provides the Stack class. Stack is a serializable class that implements the ICollection (giving the ability to know the number of items in the list) and the IEnumerable (which gives the ability to use foreach).
The Stack class is equipped with three constructors. The default constructor allows you to create a stack without primarily taking any action. Here is an example: using System;
using System.Collections;
[Serializable]
public class Sport
{
public string Name;
public uint PlayersPerTeam;
}
public static class Program
{
public static int Main(string[] args)
{
Stack players = new Stack();
return 0;
}
}
If you create a stack with this constructor, the list is primarily empty with a default capacity. If you want, before initializing the list, you can specify how much space the compiler should primarily allocate for the number of eventual items of the list. To provide this information, the Stack class is equipped with the following constructor: public Stack(int initialCapacity);
To add an item to a stack, you can call the Push() method of the Stack class. Its syntax is: public virtual void Push(object obj); The new item is passed as argument to the method. Here is an example: using System;
using System.IO;
using System.Collections;
using System.Runtime.Serialization.Formatters.Binary;
[Serializable]
public class Sport
{
public string Name;
public uint PlayersPerTeam;
}
public static class Program
{
public static int Main(string[] args)
{
Stack players = new Stack();
Sport basketball = new Sport();
basketball.Name = "Basketball";
basketball.PlayersPerTeam = 5;
players.Push(basketball);
SaveSports(players);
return 0;
}
public static void SaveSports(Stack stc)
{
FileStream fsSport = new FileStream("Sports.spt",
FileMode.Create,
FileAccess.Write);
BinaryFormatter bfSport = new BinaryFormatter();
bfSport.Serialize(fsSport, stc);
fsSport.Close();
}
}
Whenever you add a new item to the stack, the compiler increases the number of items in the list. This number is stored in the Count property of the Stack class. If you have a series of items that were created using a class that implements the ICollection interface, you can use the following constructor of the Stack class: public Stack(ICollection col); When using this constructor, pass a variable of collection class as argument. Here is an example: using System;
using System.IO;
using System.Collections;
using System.Runtime.Serialization.Formatters.Binary;
[Serializable]
public class Sport
{
public string Name;
public uint PlayersPerTeam;
}
public static class Program
{
public static int Main(string[] args)
{
Sport spt = new Sport();
ArrayList lstSports = new ArrayList();
spt.Name = "Volleyball";
spt.PlayersPerTeam = 6;
lstSports.Add(spt);
spt = new Sport();
spt.Name = "Tennis Single";
spt.PlayersPerTeam = 1;
lstSports.Add(spt);
spt = new Sport();
spt.Name = "Handball";
spt.PlayersPerTeam = 6;
lstSports.Add(spt);
Stack sports = new Stack(lstSports);
SaveSports(sports);
return 0;
}
public static void SaveSports(Stack stc)
{
FileStream fsSport = new FileStream("Sports.spt",
FileMode.Create,
FileAccess.Write);
BinaryFormatter bfSport = new BinaryFormatter();
bfSport.Serialize(fsSport, stc);
fsSport.Close();
}
}
As mentioned previously, the Stack class overrides the GetEnumerator() method by implementing the IEnumerable interface. This allows you to access each member of the stack using the foreach loop. Here is an example: using System;
using System.IO;
using System.Collections;
using System.Runtime.Serialization.Formatters.Binary;
[Serializable]
public class Sport
{
public string Name;
public uint PlayersPerTeam;
}
public static class Program
{
public static int Main(string[] args)
{
Stack sports = OpenSports();
foreach (Sport spt in sports)
{
Console.WriteLine("=-+-+-+-+-= Sport =-+-+-+-+-=");
Console.WriteLine("Sport Name: {0}", spt.Name);
Console.WriteLine("Players/Team: {0}", spt.PlayersPerTeam);
}
Console.WriteLine();
return 0;
}
public static void SaveSports(Stack stc)
{
FileStream fsSport = new FileStream("Sports.spt",
FileMode.Create,
FileAccess.Write);
BinaryFormatter bfSport = new BinaryFormatter();
bfSport.Serialize(fsSport, stc);
fsSport.Close();
}
public static Stack OpenSports()
{
FileStream fsSport = new FileStream("Sports.spt",
FileMode.Open,
FileAccess.Read);
BinaryFormatter bfSport = new BinaryFormatter();
Stack games = (Stack)bfSport.Deserialize(fsSport);
fsSport.Close();
return games;
}
}
To find out if the list contains a particular item, you can call the Contains() method of the Stack class. Its syntax is: public virtual bool Contains(object obj);
As mentioned earlier, a stack is organized so that the last item that was added to the list is the first one to be removed. To support this operation, the Stack class is equipped with the Pop() method. Its syntax is: public virtual object Pop(); When called, this method removed the last item in the stack. If you are interested to know what item was removed, this method returns it as an Object value. Here is an example of calling the method: using System;
using System.IO;
using System.Collections;
using System.Runtime.Serialization.Formatters.Binary;
[Serializable]
public class Sport
{
public string Name;
public uint PlayersPerTeam;
}
public static class Program
{
public static int Main(string[] args)
{
Stack sports = OpenSports();
foreach (Sport spt in sports)
{
Console.WriteLine("=-+-+-+-+-= Sport =-+-+-+-+-=");
Console.WriteLine("Sport Name: {0}", spt.Name);
Console.WriteLine("Players/Team: {0}", spt.PlayersPerTeam);
}
Sport one = (Sport)sports.Pop();
Console.WriteLine("The sport removed was");
Console.WriteLine("=-+-+-+-+-= Sport =-+-+-+-+-=");
Console.WriteLine("Sport Name: {0}", one.Name);
Console.WriteLine("Players/Team: {0}", one.PlayersPerTeam);
SaveSports(sports);
sports = OpenSports();
Console.WriteLine("=====================================");
foreach (Sport spt in sports)
{
Console.WriteLine("Sport Name: {0}", spt.Name);
Console.WriteLine("Players/Team: {0}", spt.PlayersPerTeam);
Console.WriteLine("=-+-+-+-+-= Sport =-+-+-+-+-=");
}
Console.WriteLine();
return 0;
}
public static void SaveSports(Stack stc)
{
FileStream fsSport = new FileStream("Sports.spt",
FileMode.Create,
FileAccess.Write);
BinaryFormatter bfSport = new BinaryFormatter();
bfSport.Serialize(fsSport, stc);
fsSport.Close();
}
public static Stack OpenSports()
{
FileStream fsSport = new FileStream("Sports.spt",
FileMode.Open,
FileAccess.Read);
BinaryFormatter bfSport = new BinaryFormatter();
Stack games = (Stack)bfSport.Deserialize(fsSport);
fsSport.Close();
return games;
}
}
The Pop() method is used to remove one item from the stack. To remove all items from the list, you can call the Clear() method whose syntax is: public virtual void Clear();
A queue is a technique of using a list so that the first item added to the list will be the first one to be removed. This is referred to as first-in first-out (FIFO). To illustrate it, when people stand in line at one cashier of a supermarket, the first customer in line in front of the cashier will be the first to be served and the first to leave the supermarket. To support queues, the .NET Framework provides the serialized Queue class that implements both the ICollection and the IEnumerable interfaces.
To create a queue, you can declare a Queue variable using one of its four constructors. The default constructor allows you to start a list without primarily adding an item to it. Here is an example: public static class Program
{
public static int Main(string[] args)
{
Queue que = new Queue();
return 0;
}
}
After this declaration, the compiler reserves some default memory space for the variable. If you want to specify how much space should be primarily allocated for the variable, you can use the following constructor: public Queue(int capacity);
The action that consists of adding an item to the queue is called "enqueue". To perform this operation, you can call the Queue.Enqueue() method whose syntax is: public virtual void Enqueue(object obj); This method takes as argument the object you want to add to the queue and places it as the first candidate to be removed. Here are examples of calling the method: using System;
using System.IO;
using System.Collections;
using System.Runtime.Serialization.Formatters.Binary;
public enum Majors
{
English,
Nursing,
Accounting,
ComputerSciences,
BusinessManagement,
MathematicalSciences,
HumanResourceDevelopment
}
[Serializable]
public class Student
{
public string FullName;
public DateTime DateOfBirth;
public Majors Major;
}
public static class Program
{
public static int Main(string[] args)
{
Queue que = new Queue();
Student std = null;
std = new Student();
std.FullName = "Donald Palau";
std.DateOfBirth = new DateTime(1988, 5, 12);
std.Major = Majors.ComputerSciences;
que.Enqueue(std);
std = new Student();
std.FullName = "Arlene Kafka";
std.DateOfBirth = new DateTime(1992, 8, 4);
std.Major = Majors.BusinessManagement;
que.Enqueue(std);
std = new Student();
std.FullName = "Hortense Moons";
std.DateOfBirth = new DateTime(1994, 10, 7);
std.Major = Majors.MathematicalSciences;
que.Enqueue(std);
SaveStudents(que);
return 0;
}
public static void SaveStudents(Queue q)
{
FileStream fsStudent = new FileStream("Students.roh",
FileMode.Create,
FileAccess.Write);
BinaryFormatter bfStudent = new BinaryFormatter();
bfStudent.Serialize(fsStudent, q);
fsStudent.Close();
}
public static Queue OpenStudents()
{
FileStream fsStudent = new FileStream("Students.roh",
FileMode.Open,
FileAccess.Read);
BinaryFormatter bfStudent = new BinaryFormatter();
Queue pupils = (Queue)bfStudent.Deserialize(fsStudent);
fsStudent.Close();
return pupils;
}
}
If you already have a list created from a class that implements the ICollection interface, you can create a queue based on that list. To do this, you would use the following constructor of the Queue class: public Queue(ICollection col); This constructor accepts an ICollection implementer as argument. Here is an example: using System;
public enum Majors
{
English,
Nursing,
Accounting,
ComputerSciences,
BusinessManagement,
MathematicalSciences,
HumanResourceDevelopment
}
public class Student
{
public string FullName;
public DateTime DateOfBirth;
public Majors Major;
}
public static class Program
{
public static int Main(string[] args)
{
Student std = null;
ArrayList lstStudents = new ArrayList();
std = new Student();
std.FullName = "Hermine Justice";
std.DateOfBirth = new DateTime(1990, 3, 24);
std.Major = Majors.English;
lstStudents.Add(std);
std = new Student();
std.FullName = "Patricia Palermo";
std.DateOfBirth = new DateTime(1989, 12, 20);
std.Major = Majors.BusinessManagement;
lstStudents.Add(std);
Queue que = new Queue(lstStudents);
return 0;
}
}
Remember that the first item added to a queue stays in front of all others that would be added. To get (only) the first item of a queue, the Queue class is equipped with a method named Peek(). Its syntax is: public virtual object Peek(); This method returns an Object object that represents the first item of the queue (remember to cast it to your particular object if necessary). Here are two examples of calling it: using System;
using System.Collections;
public enum Majors
{
English,
Nursing,
Accounting,
ComputerSciences,
BusinessManagement,
MathematicalSciences,
HumanResourceDevelopment
}
public class Student
{
public string FullName;
public DateTime DateOfBirth;
public Majors Major;
}
public static class Program
{
public static int Main(string[] args)
{
Queue que = new Queue();
Student std = null;
std = new Student();
std.FullName = "Donald Palau";
std.DateOfBirth = new DateTime(1988, 5, 12);
std.Major = Majors.ComputerSciences;
que.Enqueue(std);
std = new Student();
std.FullName = "Arlene Kafka";
std.DateOfBirth = new DateTime(1992, 8, 4);
std.Major = Majors.BusinessManagement;
que.Enqueue(std);
Console.WriteLine("The current first item of the queue is");
Student s1 = (Student)que.Peek();
Console.WriteLine("== Student Information ==");
Console.WriteLine("Full Name: {0}", s1.FullName);
Console.WriteLine("Date of Birth: {0:d}", s1.DateOfBirth);
Console.Write("Major: ");
switch (s1.Major)
{
case Majors.English:
Console.WriteLine("English");
break;
case Majors.Nursing:
Console.WriteLine("Nursing");
break;
case Majors.Accounting:
Console.WriteLine("Accounting");
break;
case Majors.ComputerSciences:
Console.WriteLine("Computer Sciences");
break;
case Majors.BusinessManagement:
Console.WriteLine("Business Management");
break;
case Majors.MathematicalSciences:
Console.WriteLine("Mathematical Sciences");
break;
case Majors.HumanResourceDevelopment:
Console.WriteLine("Human Resource Development");
break;
}
Console.WriteLine("--------------------------------------------");
std = new Student();
std.FullName = "Hortense Moons";
std.DateOfBirth = new DateTime(1994, 10, 7);
std.Major = Majors.MathematicalSciences;
que.Enqueue(std);
Console.WriteLine("The current first item of the queue is");
Student s2 = (Student)que.Peek();
Console.WriteLine("== Student Information ==");
Console.WriteLine("Full Name: {0}", s2.FullName);
Console.WriteLine("Date of Birth: {0:d}", s2.DateOfBirth);
Console.Write("Major: ");
switch (s2.Major)
{
case Majors.English:
Console.WriteLine("English");
break;
case Majors.Nursing:
Console.WriteLine("Nursing");
break;
case Majors.Accounting:
Console.WriteLine("Accounting");
break;
case Majors.ComputerSciences:
Console.WriteLine("Computer Sciences");
break;
case Majors.BusinessManagement:
Console.WriteLine("Business Management");
break;
case Majors.MathematicalSciences:
Console.WriteLine("Mathematical Sciences");
break;
case Majors.HumanResourceDevelopment:
Console.WriteLine("Human Resource Development");
break;
}
Console.WriteLine("--------------------------------------------");
return 0;
}
}
This would produce: The current first item of the queue is == Student Information == Full Name: Donald Palau Date of Birth: 5/12/1988 Major: Computer Sciences -------------------------------------------- The current first item of the queue is == Student Information == Full Name: Donald Palau Date of Birth: 5/12/1988 Major: Computer Sciences -------------------------------------------- Press any key to continue . . . To give you access to the items of a queue, the Queue class overrides the GetEnumerator() method of the IEnumerable class that it implements. This allows you to use the foreach loop to continuously enumerate the members of a queue. Here is an example: using System;
using System.IO;
using System.Collections;
using System.Runtime.Serialization.Formatters.Binary;
public enum Majors
{
English,
Nursing,
Accounting,
ComputerSciences,
BusinessManagement,
MathematicalSciences,
HumanResourceDevelopment
}
[Serializable]
public class Student
{
public string FullName;
public DateTime DateOfBirth;
public Majors Major;
}
public static class Program
{
public static int Main(string[] args)
{
Student std = null;
Queue lstStudents = OpenStudents();
std = new Student();
std.FullName = "Hermine Justice";
std.DateOfBirth = new DateTime(1990, 3, 24);
std.Major = Majors.English;
lstStudents.Enqueue(std);
std = new Student();
std.FullName = "Patricia Palermo";
std.DateOfBirth = new DateTime(1989, 12, 20);
std.Major = Majors.BusinessManagement;
lstStudents.Enqueue(std);
SaveStudents(lstStudents);
lstStudents = OpenStudents();
ShowStudents(lstStudents);
return 0;
}
public static void ShowStudents(Queue q)
{
foreach (Student s in q)
{
Console.WriteLine("== Student Information ==");
Console.WriteLine("Full Name: {0}", s.FullName);
Console.WriteLine("Date of Birth: {0:d}", s.DateOfBirth);
Console.Write("Major: ");
switch (s.Major)
{
case Majors.English:
Console.WriteLine("English");
break;
case Majors.Nursing:
Console.WriteLine("Nursing");
break;
case Majors.Accounting:
Console.WriteLine("Accounting");
break;
case Majors.ComputerSciences:
Console.WriteLine("Computer Sciences");
break;
case Majors.BusinessManagement:
Console.WriteLine("Business Management");
break;
case Majors.MathematicalSciences:
Console.WriteLine("Mathematical Sciences");
break;
case Majors.HumanResourceDevelopment:
Console.WriteLine("Human Resource Development");
break;
}
Console.WriteLine("--------------------------------------------");
}
}
public static void SaveStudents(Queue q)
{
FileStream fsStudent = new FileStream("Students.roh",
FileMode.Create,
FileAccess.Write);
BinaryFormatter bfStudent = new BinaryFormatter();
bfStudent.Serialize(fsStudent, q);
fsStudent.Close();
}
public static Queue OpenStudents()
{
FileStream fsStudent = new FileStream("Students.roh",
FileMode.Open,
FileAccess.Read);
BinaryFormatter bfStudent = new BinaryFormatter();
Queue pupils = (Queue)bfStudent.Deserialize(fsStudent);
fsStudent.Close();
return pupils;
}
}
This would produce: == Student Information == Full Name: Donald Palau Date of Birth: 5/12/1988 Major: Computer Sciences -------------------------------------------- == Student Information == Full Name: Arlene Kafka Date of Birth: 8/4/1992 Major: Business Management -------------------------------------------- == Student Information == Full Name: Hortense Moons Date of Birth: 10/7/1994 Major: Mathematical Sciences -------------------------------------------- == Student Information == Full Name: Hermine Justice Date of Birth: 3/24/1990 Major: English -------------------------------------------- == Student Information == Full Name: Patricia Palermo Date of Birth: 12/20/1989 Major: Business Management -------------------------------------------- Press any key to continue . . .
The process of removing an item from a queue is called "dequeue". To assist you with performing this operation, the Queue class is equipped with a method named Dequeue. Its syntax is: public virtual object Dequeue(); The primary purpose of this method is to delete the first item of the Queue list. If you are interested to know what item was deleted, this method returns it. To remove all items from the queue, you can call the Clear() method of the class. Its syntax is: public virtual void Clear();
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Practical
Learning: Introducing Hash Tables