Module 7: Strings, Arrays, and Collections |
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" .NET Framework Collections
Topic Objective
To introduce the topics in the section.
Lead-in
The System.Collections namespace contains interfaces and classes that define various collections of objects, such as lists, queues, arrays, hashtables, and dictionaries.
!Examples of System.Collections Classes
!Lists
!Dictionaries
!SortedList
!Collection Usage Guidelines
!Type Safety and Performance
*****************************ILLEGAL FOR NON-TRAINER USE******************************
The System.Collections namespace contains interfaces and classes that define various collections of objects, such as lists, queues, arrays, hashtables, and dictionaries.
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Module 7: Strings, Arrays, and Collections |
Examples of System.Collections Classes
Topic Objective
To show some of the collection classes in the
System.Collections
namespace.
Lead-in
Let’s look briefly at some of the collection classes in the
System.Collections
namespace.
!ArrayList
#Implements IList by using a dynamically-sized array
!DictionaryBase
#Provides abstract base class for strongly-typed collection of associated keys and values
!Hashtable
#Represents a collection of keys and values that are organized around the key’s hash code
!SortedList
#Represents the collection of keys and values, sorted by keys and accessible by key and index
!BitArray, Queue, Stack, CollectionBase, ReadOnlyCollectionBase
*****************************ILLEGAL FOR NON-TRAINER USE******************************
Do not spend a lot of time on this slide. Just introduce students to some commonly used collection classes and encourage them to refer to the .NET Framework SDK for more information.
The following table shows some of the collection classes in the
System.Collections namespace.
Class |
Description |
ArrayList |
Implements the IList interface by using an array whose |
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size is dynamically increased as required. |
BitArray |
Manages a compact array of bit values, which are |
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represented as Booleans, where true indicates that the bit |
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is on (1) and false indicates the bit is off (0). |
CollectionBase |
Provides the abstract base class (MustInherit in |
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Microsoft Visual Basic®) for a strongly-typed collection. |
DictionaryBase |
Provides the abstract base class (MustInherit in |
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Visual Basic) for a strongly-typed collection of |
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associated keys and values. |
Hashtable |
Represents a collection of associated keys and values that |
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are organized around the hash code of the key. |
Queue |
Represents a first-in, first-out collection of objects. |
ReadOnlyCollectionBase |
Provides the abstract base class (MustInherit in |
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Visual Basic) for a strongly-typed read-only collection. |
SortedList |
Represents a collection of associated keys and values that |
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are sorted by the keys and are accessible by key and by |
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index. |
Stack |
Represents a simple last-in-first-out collection of type |
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Object. |
Module 7: Strings, Arrays, and Collections |
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Lists
Topic Objective
To describe the public instance members that the IList interface implements.
Lead-in
IList is an interface for classes that represent an ordered collection of objects that can be individually indexed. Array, ArrayList, StringCollection, and TreeNodeCollection are some of the classes that implement IList.
!IList – Interface for Classes That Represent an Ordered Collection of Objects That Can Be Individually Indexed
!Some Classes That Implement IList
#Array, ArrayList, StringCollection, and
TreeNodeCollection
!Methods Include:
#Add, Clear, Contains, Insert, IndexOf, Remove, and
RemoveAt
*****************************ILLEGAL FOR NON-TRAINER USE******************************
IList is an interface for classes that represent an ordered collection of objects that can be individually indexed. Array, ArrayList, StringCollection, and TreeNodeCollection are some of the classes that implement IList.
The following tables describe the public instance properties that the IList interface implements.
Property |
Use |
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IsFixedSize |
When implemented by a class, gets a value indicating whether the IList |
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has a fixed size. |
IsReadOnly |
When implemented by a class, gets a value indicating whether the IList |
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is read-only. |
Item |
When implemented by a class, gets or sets the element at the specified |
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index. |
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In C#, this property is the indexer for the IList class. |
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The following table describes the public instance methods that the IList interface defines.
Method |
Use |
Add |
When implemented by a class, adds an item to the IList. |
Clear |
When implemented by a class, removes all items from the IList. |
Contains |
When implemented by a class, determines whether the IList contains a |
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specific value. |
IndexOf |
When implemented by a class, determines the index of a specific item in |
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the IList. |
Insert |
When implemented by a class, inserts an item to the IList at the |
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specified position. |
Remove |
When implemented by a class, removes the first occurrence of a specific |
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object from the IList. |
RemoveAt |
When implemented by a class, removes the IList item at the specified |
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index. |
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Demonstration: ArrayList
Topic Objective
To demonstrate how ArrayList implements the IList interface by using an array whose size is dynamically increased as required.
Lead-in
In this demonstration, ArrayList implements the IList interface by using an array whose size is dynamically increased as required.
*****************************ILLEGAL FOR NON-TRAINER USE******************************
In this demonstration, ArrayList implements the IList interface by using an array whose size is dynamically increased as required.
using System;
using System.Collections;
class listSample
{
public static void Main(string[] args) { ArrayList fruit = new ArrayList(); fruit.Add("Apple"); fruit.Add("Pear"); fruit.Add("Orange"); fruit.Add("Banana");
Console.WriteLine ("\nList Contains:"); foreach (string item in fruit) {
Console.WriteLine(item);
}
Console.WriteLine (
"\nResult of Contains method for Kiwi: {0}", fruit.Contains("Kiwi"));
Console.WriteLine (
"\nAdding Kiwi at Orange:");
fruit.Insert(fruit.IndexOf("Orange"),"Kiwi"); Console.WriteLine ("\nList Contains:"); foreach (string item in fruit) {
Console.WriteLine(item);
}
(Code continued the following page.)
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Console.WriteLine (
"\nResult of Contains method for Kiwi: {0}", fruit.Contains("Kiwi"));
Console.WriteLine (
"\r\nPress Return to exit."); Console.Read();
}
}
The preceding code example displays the following output to the console:
List Contains:
Apple
Pear
Orange
Banana
Result of Contains method for Kiwi: False
Adding Kiwi at Orange:
List Contains:
Apple
Pear
Kiwi
Orange
Banana
Result of Contains method for Kiwi: True
Press Return to exit.
Module 7: Strings, Arrays, and Collections |
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Dictionaries
Topic Objective
To describe the IDictionary interface and the classes that it implements.
Lead-in
IDictionary is an interface for collections of associated keys and values.
!IDictionary is an Interface for Collections of Associated Keys and Values
#Each association must have a unique non-null key, but the value of an association can be any object reference, including a null reference
!Collection Classes That Implement IDictionary Include
#Hashtable, DictionaryBase, and SortedList
!Methods Include:
#Add, Clear, Contains, GetEnumerator, and Remove
*****************************ILLEGAL FOR NON-TRAINER USE******************************
IDictionary is an interface for collections of associated keys and values. Each association must have a unique non-null key, but the value of an association can be any object reference, including a null reference.
Hashtable, DictionaryBase, and SortedList are examples of collection classes that implement IDictionary.
The IDictionary interface allows the contained keys and values in the items in a collection to be enumerated, but it does not imply any particular sort order. The IDictionaryEnumerator interface inherits from IEnumerator and adds members to return the object’s Key and Value fields individually or in a
DictionaryEntry structure.
IDictionary implementations can be divided into the following categories:
!Read-only
You cannot modify a read-only IDictionary.
!Fixed-size
You cannot add or remove elements from a fixed-size IDictionary, but you can modify existing elements.
!Variable-size
You can add, remove, or modify elements in a variable-size IDictionary.
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The following table describes some of the public instance properties that the IDictionary interface implements.
Property |
Use |
IsFixedSize |
When implemented by a class, gets a value indicating whether the |
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IDictionary has a fixed size. |
IsReadOnly |
When implemented by a class, gets a value indicating whether the |
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IDictionary is read-only. |
Item |
When implemented by a class, gets or sets the element at the |
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specified index. |
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In C#, this property is the indexer for the class. |
Keys |
When implemented by a class, gets an ICollection containing the |
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keys of the IDictionary. |
Values |
When implemented by a class, gets an ICollection containing the |
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values in the IDictionary. |
The following table describes some of the public instance methods that the IDictionary interface implements.
Method |
Use |
Add |
When implemented by a class, adds an entry with the provided |
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key and value to the IDictionary. |
Clear |
When implemented by a class, removes all elements from the |
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IDictionary. |
Contains |
When implemented by a class, determines whether the |
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IDictionary contains an entry with the specified key. |
GetEnumerator |
When implemented by a class, returns an |
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IDictionaryEnumerator for the IDictionary. |
Remove |
When implemented by a class, removes the entry with the |
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specified key from the IDictionary. |
For a complete list of the members of the IDictionary interface, see “IDictionary Members” in the .NET Framework SDK documentation.
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Demonstration: Hashtable
Topic Objective
To demonstrate how to create a hash table that is used for searches.
Lead-in
The Hashtable class represents a collection of associated keys and values that are organized on the basis of the keys’ hash code.
*****************************ILLEGAL FOR NON-TRAINER USE******************************
The Hashtable class represents a collection of associated keys and values that are organized on the basis of the keys’ hash code. The objects that are used as keys in a Hashtable must implement or inherit the Object.GetHashCode and Object.Equals methods. If key equality were simply reference equality, the inherited implementation of these methods would suffice.
Furthermore, these methods must produce the same results when they are called with the same parameters while the key exists in the Hashtable. Key objects must be immutable as long as they are used as keys in the Hashtable.
The foreach statement of the C# language requires the type of the elements in the collection. Because each element of the Hashtable is a key-and-value pair, the element type is not the type of the key or the type of the value. Instead, the element type is DictionaryEntry, as in the following example:
foreach (DictionaryEntry myEntry in myHashtable) {...}
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The code in this demonstration creates a hash table of employee numbers and names, and searches the table for an employee by number and by name.
using System;
using System.Collections;
class HashTableSample
{
public static void Main(String[] args)
{
//create hash table of employee numbers and names Hashtable table = new Hashtable(); table.Add("0123","Jay"); table.Add("0569","Brad"); table.Add("1254","Brian"); table.Add("6839","Seth"); table.Add("3948","Rajesh"); table.Add("1930","Lakshan"); table.Add("9341","Kristian"); printTable(table);
//now we'll look to see if an employee is in the table //by key
Console.Write(
"Search for employee by key, enter ID ==-> "); string input = Console.ReadLine();
if (table.Contains(input)) { Console.WriteLine("Found {0} in the list.",input);
}
else {
Console.WriteLine("Employee {0} not found.",input);
}
//by value Console.Write(
"Search for employee by value, enter name ==-> "); input = Console.ReadLine();
if (table.ContainsValue(input)) { Console.WriteLine("Found {0} in the list.",input);
}
else {
Console.WriteLine("Employee {0} not found.",input);
}
printTable(table);
// remove an employee by key
Console.Write("Remove employee by key, enter ID ==-> "); input = Console.ReadLine();
table.Remove(input);
printTable(table);
Console.WriteLine ("\r\nPress Return to exit."); Console.Read();
}
(Code continued on the following page.)
