Asp.Net Tutorials

and makeup of the array. With all the collections we’ll examine in this chapter, this is
no
longer a concern. Adding, Removing, and Indexing Elements in an ArrayList The ArrayList class contains a number of methods for adding and removing Objects from the collection. These include Add, AddRange, Insert, Remove, RemoveAt, RemoveRange, and Clear, all of which we’ll examine in Listing 2.1. The output is shown in Figure 2.1. LISTING 2.1 For Sequentially Accessed Collections, Use the ArrayList 2: 3: Sub Page_Load(source as Object, e as EventArgs) 4: ‘ Create two ArrayLists, aTerritories and aStates 5: Dim aTerritories as New ArrayList 6: Dim aStates as New ArrayList 7: 8: ‘ Use the Add method to add the 50 states of the US 9: aStates.Add(“Alabama”) 10: aStates.Add(“Alaska”) 11: aStates.Add(“Arkansas”) 12: ‘ ... 13: aStates.Add(“Wyoming”)
15: ‘ Build up our list of territories, which includes
16: ‘ all 50 states plus some additional countries 17: aTerritories.AddRange(aStates) ‘ add all 50 states 18: aTerritories.Add(“Guam”) 19: aTerritories.Add(“Puerto Rico”) 20: 21: ‘ We’d like the first territory to be the District of Columbia, 22: ‘ so we’ll explicitly add it to the beginning of the ArrayList 23: aTerritories.Insert(0, “District of Columbia”) 24: 25: ‘ Display all of the territories with a for loop 26: lblTerritories.Text = “There are “ & aTerritories.Count & _ 27: “territories...” 28: 29: Dim i as Integer 30: For i = 0 to aTerritories.Count - 1 31: lblTerritories.Text = lblTerritories.Text & _ 32: aTerritories(i) & “”

Asp.Net Tutorials

these collections can literally store anything! For example, you could use a single
collection to
store a couple of integers, an instance of a classic COM component, a string, a date/time,
and two instances of a custom-written .NET component. Most of the examples in this section use collections to house primitive data types (strings, integers, doubles). However, Listing
2.1 illustrates a collection of collections—that is, a collection type that stores entire collections as
each of its elements! Throughout this section we’ll examine five collections the .NET Framework offers
developers: the ArrayList, the Hashtable, the SortedList, the Queue, and the Stack. As you study each of these collections, realize that they all have many similarities. For example, each type
of collection can be iterated through element-by-element using a For Each ... Next loop in VB (or a foreach loop in C#). Each collection type has a number of similarly named functions
that perform the same tasks. For example, each collection type has a Clear method that removes
all elements from the collection, and a Count property that returns the number of elements in
the collection. In fact, the last subsection “Similarities Among the Collection Types”
examines the common traits found among the collection types. Working with the ArrayList Class The first type of collection we’ll look at is the ArrayList. With an ArrayList, each item
is stored in sequential order and is indexed numerically. In our following examples, keep in
mind that the developer need not worry himself with memory allocation. With the standard array,
the