Learning Visual Basic .NET

Chapter 15. Collection Interfaces and Types

A collection is a container that holds a group of objects. Collections are used to hold all the strings in a listbox, to hold all the employees in a company, to hold all the controls on a page, and so forth. You’ve already seen the simplest collection, the array (see Chapter 14). An array is a collection that provides an indexed list of elements, all of the same type.

The .NET Framework provides a number of already built and tested collection classes, including the ArrayList, Collection, Queue, and Stack. This chapter will explain how to use these collections and will provide examples of their use.

The Collection Interfaces

Every collection has certain shared characteristics. These are captured by the collection interfaces. The .NET Framework provides standard interfaces for enumerating, comparing, and creating collections.

Tip

Chapter 13 introduced interfaces, which create a contract that a class can fulfill. Implementing an interface allows clients of the class to know exactly what to expect from the class.

By implementing the collection interfaces, your custom class can provide the same semantics as the collection classes available through the .NET Framework. Table 15-1 lists the key collection interfaces and their uses.

Table 15-1. The collection interfaces

Interface	Purpose
IEnumerable	Designates a class that can be enumerated
IEnumerator	A class that iterates over a collection; supports the For Each loop
ICollection ...