Collection Basics

Collections are groups of items or as in C#, objects. In C# .NET, each built-in collection implements the ICollection interface. Because the ICollection interface inherits from the IEnumerable interface, each built-in collection also implements the IEnumerable interface. In the following sections, you will gain a basic knowledge of what collections are and how they operate .

Understanding the Basic Collection Interfaces

These are collections that are provided with C#, out of the box; they all reside in the System.Collections namespace. Each implements the ICollection interface. Table 5.2 shows the members of the ICollection interface.

Table 5.2. ICollection Members

Table 5.3 lists the collection interfaces.

Table 5.3. Collection Interfaces

Iterating Through Collections

Because the ICollection interface inherits from the IEnumerable interface, collections provide the ability to iterate over the items that the collection contains.

Iterating through a collection can be done in a few different ways. Because all collections implement the IEnumerable interface, you can use the IEnumberable.GetEnumerator to return an enumerator that is capable of iterating through the collection.

Table 5.4. Methods and Properties of an Enumerator

The following code fragment demonstrates how to iterate through a collection:

protected void PrintList(System.Collections.ArrayList list)
{
  IEnumerator enumerator = list.GetEnumerator();
  while(enumerator.MoveNext())
  {
    System.Console.WriteLine((string) enumerator.Current);
  }
}