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The Class Types of System.Collections

As explained in the previous chapter, interfaces by themselves are not very useful until they are

implemented by a given class or structure. Table 10-2 provides a rundown of the core classes in the

System.Collections namespace and the key interfaces they support.

Table 10-2.

Classes of System.Collections

System.Collections Class

Meaning in Life

Key Implemented Interfaces

ArrayList

Represents a dynamically sized array 

IList, ICollection,

of objects.

IEnumerable, and

ICloneable

Hashtable

Represents a collection of objects 

IDictionary, ICollection,

identified by a numerical key. 

IEnumerable, and 

Custom types stored in a Hashtable

ICloneable

should always override System.

Object.GetHashCode().

Queue

Represents a standard first-in, 

ICollection, ICloneable,

first-out (FIFO) queue.

and IEnumerable

SortedList

Like a dictionary; however, the 

IDictionary, ICollection,

elements can also be accessed 

IEnumerable, and 

by ordinal position (e.g., index).

ICloneable

Stack

A last-in, first-out (LIFO) queue 

ICollection, ICloneable,

providing push and pop (and peek) 

and IEnumerable

functionality.

In addition to these key types, System.Collections defines some minor players (at least in

terms of their day-to-day usefulness) such as BitArray, CaseInsensitiveComparer, and

CaseInsensitiveHashCodeProvider. Furthermore, this namespace also defines a small set of abstract

base classes (CollectionBase, ReadOnlyCollectionBase, and DictionaryBase) that can be used to

build strongly typed containers.

As you begin to experiment with the System.Collections types, you will find they all tend to

share common functionality (that’s the point of interface-based programming). Thus, rather than

listing out the members of each and every collection class, the next task of this chapter is to illus-

trate how to interact with three common collection types: ArrayList, Queue, and Stack.

Once you understand the functionality of these types, gaining an understanding of the remain-

ing collection classes (such as the Hashtable) should naturally follow; especially since each of the

types is fully documented within the .NET Framework 3.5 documentation.

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