Framework Fundamentals in Visual C#.NET

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Strings of type System.String are immutable in .NET. That means any change to a string causes the runtime to create a new string and abandon the old one. That happens invisibly, and many programmers might be surprised to learn that the following code allocates four new strings in memory:

' VB Dim s As String s = "wombat" s += " kangaroo" s += " wallaby" s += " koala" Console.WriteLine(s) // C# string s; s = "wombat"; s += " kangaroo"; s += " wallaby"; s += " koala"; Console.WriteLine(s); // // // // "wombat" "wombat kangaroo" "wombat kangaroo wallaby" "wombat kangaroo wallaby koala" ' ' ' ' "wombat" "wombat kangaroo" "wombat kangaroo wallaby" "wombat kangaroo wallaby koala"

Only the last string has a reference; the other three will be disposed of during garbage collection. Avoiding these types of temporary strings helps avoid unnecessary garbage collection, which improves performance. There are several ways to avoid temporary strings:

Use the String class s Concat, Join, or Format methods to join multiple items in a single statement. Use the StringBuilder class to create dynamic (mutable) strings.

The StringBuilder solution is the most flexible because it can span multiple statements. The default constructor creates a buffer 16 bytes long, which grows as needed. You can specify an initial size and a maximum size if you like. The following code demonstrates using StringBuilder:

' VB Dim sb As New System.Text.StringBuilder(30) sb.Append("wombat") ' Build string. sb.Append(" kangaroo") sb.Append(" wallaby") sb.Append(" koala") Dim s as String = sb.ToString ' Copy result to string. Console.WriteLine(s)

// C# System.Text.StringBuilder sb = new System.Text.StringBuilder(30); sb.Append("wombat"); // Build string. sb.Append(" kangaroo"); sb.Append(" wallaby"); sb.Append(" koala"); string s = sb.ToString(); // Copy result to string. Console.WriteLine(s);

Another subtle but important feature of the String class is that it overrides operators from System.Object. Table 1-4 lists the operators the String class overrides.

Table 1-4

Visual Basic + or & =

Action on System.String Joins two strings to create a new string. Returns True if two strings have the same contents; False if they are different. The inverse of the equality operator. Copies the contents of one string into a new one. This causes strings to behave like value types, even though they are implemented as reference types.

!= =

Arrays are declared using parentheses (in Visual Basic) or square braces (in C#) as part of the declaration. As with the String type, System.Array provides members for working with its contained data. The following code declares an array with some initial data and then sorts the array:

' VB ' Declare and initialize an array. Dim ar() As Integer = {3, 1, 2} ' Call a shared/static array method. Array.Sort(ar)

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' Display the result. Console.WriteLine("{0}, {1}, {2}", ar(0), ar(1), ar(2)) // C# // Declare and initialize an array. int[] ar = { 3, 1, 2 }; // Call a shared/static array method. Array.Sort(ar); // Display the result. Console.WriteLine("{0}, {1}, {2}", ar[0], ar[1], ar[2]);

Streams are another very common type because they are the means for reading from and writing to the disk and communicating across the network. The System.IO.Stream type is the base type for all task-specific stream types. Table 1-5 shows some of the most commonly used stream types. In addition, network streams are found in the System.Network.Sockets namespace, and encrypted streams are found in the System.Security.Cryptography namespace.

Table 1-5

Use to Create a base stream used to write to or read from a file Create a base stream used to write to or read from memory Read data from the stream Write data to the stream

The simplest stream classes are StreamReader and StreamWriter, which enable you to read and write text files. You can pass a filename as part of the constructor, enabling you to open a file with a single line of code. After you have processed a file, call the Close method so that the file does not remain locked. The following code, which requires the System.IO namespace, demonstrates how to write to and read from a text file:

' VB ' Create and write to a text file Dim sw As StreamWriter = New StreamWriter("text.txt") sw.WriteLine("Hello, World!") sw.Close