Collections in .Net

Namespace: System.Collections

Types of Collections:

Class	Description
ArrayList	Implements the IList interface using an array whose size is dynamically increased as required.
BitArray	Manages a compact array of bit values, which are represented as Booleans, where true indicates that the bit is on (1) and false indicates the bit is off (0).
CaseInsensitiveComparer	Compares two objects for equivalence, ignoring the case of strings.
CaseInsensitiveHashCodeProvider	Obsolete. Supplies a hash code for an object, using a hashing algorithm that ignores the case of strings.
CollectionBase	Provides the abstract base class for a strongly typed collection.
Comparer	Compares two objects for equivalence, where string comparisons are case-sensitive.
DictionaryBase	Provides the abstract base class for a strongly typed collection of key/value pairs.
Hashtable	Represents a collection of key/value pairs that are organized based on the hash code of the key.
Queue	Represents a first-in, first-out collection of objects.
ReadOnlyCollectionBase	Provides the abstract base class for a strongly typed non-generic read-only collection.
SortedList	Represents a collection of key/value pairs that are sorted by the keys and are accessible by key and by index.
Stack	Represents a simple last-in-first-out (LIFO) non-generic collection of objects.

Intefaces:

Interface	Description
ICollection	Defines size, enumerators, and synchronization methods for all nongeneric collections.
IComparer	Exposes a method that compares two objects.
IDictionary	Represents a nongeneric collection of key/value pairs.
IDictionaryEnumerator	Enumerates the elements of a nongeneric dictionary.
IEnumerable	Exposes the enumerator, which supports a simple iteration over a non-generic collection.
IEnumerator	Supports a simple iteration over a nongeneric collection.
IEqualityComparer	Defines methods to support the comparison of objects for equality.
IHashCodeProvider	Obsolete. Supplies a hash code for an object, using a custom hash function.
IList	Represents a non-generic collection of objects that can be individually accessed by index.

ArrayList

The ArrayList class is a simple, unordered container for objects of any type.

Add, AddRange(To add items from another collection or ArrayList),

Array List supports the IEnumerable interface that exposes GetEnumerator method that return IEnumerator interface. IEnumerator have a property called Current and two methods including MoveNext and Reset.

ArrayList collection = new ArrayList();

IEnumerator e = collection.GetEnumerator();

While(e.MoveNext())

{

                Console.WriteLine(e.Current);

}

OR

foreach(object o in collection)

                Console.WriteLine(o.ToString());

Consistent Interfaces in Collections:

Like IEnumerable interface, all collection classes inherit from ICollection interface that intern inherit from IEnumerable interface. ICollection interface provide you the following Proepries:

Name	Description
Count	Gets the number of elements contained in the ICollection.
IsSynchronized	Gets a value indicating whether access to the ICollection is synchronized (thread safe).
SyncRoot	Gets an object that can be used to synchronize access to the ICollection.

Important Methods:

Name	Description
CopyTo	Copies the elements of the ICollection to an Array, starting at a particular Array index.
GetEnumerator	Returns an enumerator that iterates through a collection. (Inherited from IEnumerable.)

Some simple list type collections inherit from IList interface that intern inherit from ICollection interface.

IList Interface’s most important properties are:

Name	Description
Count	Gets the number of elements contained in the ICollection. (Inherited from ICollection.)
IsFixedSize	Gets a value indicating whether the IList has a fixed size.
IsReadOnly	Gets a value indicating whether the IList is read-only.
IsSynchronized	Gets a value indicating whether access to the ICollection is synchronized (thread safe). (Inherited from ICollection.)
Item	Gets or sets the element at the specified index.
SyncRoot	Gets an object that can be used to synchronize access to the ICollection. (Inherited from ICollection.)

IList Interface’s most important Methods are:

Name	Description
Add	Adds an item to the IList.
Clear	Removes all items from the IList.
Contains	Determines whether the IList contains a specific value.
CopyTo	Copies the elements of the ICollection to an Array, starting at a particular Array index. (Inherited from ICollection.)
GetEnumerator	Returns an enumerator that iterates through a collection. (Inherited from IEnumerable.)
IndexOf	Determines the index of a specific item in the IList.
Insert	Inserts an item to the IList at the specified index.
Remove	Removes the first occurrence of a specific object from the IList.
RemoveAt	Removes the IList item at the specified index.

Inheritance Sequence:

IEnumerator → IEnumerable → ICollection → IList

Sorting Items:

                        To sort item in an ArrayList, simply call ArrayList.Sort method. This method works using Comparer class. 
Comparer is the default implementation of the ICompare interface. One can specify any other Compare class that implements the IComparer interface. Like another built-in implementation that perform Case Insensitive comparison i.e. CaseInsensitiveComparer.