Visual Basic.NET How to Program (PDF)

Chapter 15 Strings, Characters and Regular Expressions 635
character set (see Appendix E, ASCII character set). To learn the integer equivalents of
many common Unicode characters, see Appendix F, Unicode.
A string is a series of characters treated as a single unit. These characters can be uppercase
letters, lowercase letters, digits and various special characters, such as +, -, *, /, $
and others. A string is an object of class String in the System namespace. We write
string literals, or string constants (often called literal String objects), as sequences of
characters in double quotation marks, as follows:
"John Q. Doe"
"9999 Main Street"
"Waltham, Massachusetts"
"(201) 555-1212"
A declaration can assign a String literal to a String reference. The declaration
Dim color As String = "blue"
initializes String reference color to refer to the String literal object "blue".
Performance Tip 15.1
If there are multiple occurrences of the same String literal object in an application, a single
copy of the String literal object will be referenced from each location in the program
that uses that String literal. It is possible to share the object in this manner, because
String literal objects are implicitly constant. Such sharing conserves memory. 15.1
15.3 String Constructors
Class String provides three constructors for initializing String objects in various
ways. Figure 15.1 demonstrates the use of three of the constructors.
1 ' Fig. 15.1: StringConstructor.vb
2 ' Demonstrating String class constructors.
3
4 Imports System.Windows.Forms
5
6 Module modStringConstructor
7
8 Sub Main()
9 Dim characterArray As Char()
10 Dim output As String
11 Dim quotes As Char = ChrW(34)
12 Dim originalString, string1, string2, string3, _
13 string4 As String
14
15 characterArray = New Char() {"b"c, "i"c, "r"c, _
16 "t"c, "h"c, " "c, "d"c, "a"c, "y"c}
17
18 ' string initialization
19 originalString = "Welcome to VB.NET Programming!"
20 string1 = originalString
21 string2 = New String(characterArray)
Fig. 15.1 String constructors (part 1 of 2).